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Video for Linux Two API Specification

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1. ks pacbell net gt VERSION 2 5 69 h VERSION 2 5 0 linux compiler h need _ user E OWNER 1 It will be removed for 2 6 15 x Can capture Can tune x Does teletext Overlay onto frame buffer Overlay by chromakey x Can clip Uses th fram buffer m Scalable Monochrome only x Can Can decode Can encode Can decode Can encode MP MP capture subareas of EG streams EG streams MJP MJP mory the image x x EG streams EG streams x 179 Appendix A Video For Linux Two Header File define VFL TYPE GRABBER define VFL TYPE VBI define VFL TYPE RADIO define VFL TYPE VTX WN FO struct video_device device info if LINUX VERSION CODE gt KERNEL VERSION 2 6 0 struct device dev endif char name 32 int type v4ll int type2 v412 x int hardware int minor device ops callbacks struct file operations xfops void xrelease struct video device vfd if LINUX VERSION CODE lt KERNEL VERSION 2 5 0 old obsolete interfac dropped in 2 5 x don t use it x int xopen struct video device x int mode void close struct video device long xread struct video device x char unsigned long int n long xwrite struct video device
2. The driver may clamp the value or return if 1 ioctl fd VIDIOC S CTRL amp control amp amp errno ERANGE perror VIDIOC_S_CTRL exit EXIT FAILURE Ignore if V4L2_CID_CONTRAST is unsupported x else if errno EINVAL perror VIDIOC_G_CTRL exit EXIT_FAILURE control id E TRUI control value ioctl Errors ignored fd VIDIOC S CT VAL2 CID AUDIO MUTE silence x RL amp control 13 Chapter 1 Common API Elements 1 9 Data Formats 1 9 1 Data Format Negotiation Different devices exchange different kinds of data with applications for example video images raw or sliced VBI data RDS datagrams Even within one kind many different formats are possible in particular an abundance of image formats Although drivers must provide a default and the selection persists across closing and reopening a device applications should always negotiate a data format before engaging in data exchange Negotiation means the application asks for a particular format and the driver selects and reports the best the hardware can do to satisfy the request Of course applications can also just query the current selection A single mechanism exists to negotiate all data formats using the aggregate struct v412 format and the VIDIOC_G_FMT and VIDIOC S FMT ioctls Additionally the VIDIOC_TRY_FMT ioctl can be used to examine what the hardware could do wi
3. s aan lt i Oe NF O e lt 3 D x V 8 E lt lt 3 A S N Re a 10 TT 14 15 IT 18 I9 See aoe Fo ae LEARNS RS lt a lt sscaccd ACE ORE OMNE EU MEET 21 22 23 24 294 26 25 28 29y 30 33 34 36 37 38 39 46 47 48 49 wu RUE TET USATE PRC EE IN RESLIIDR CROSS VN RU AKA RR S ZSddiddddddidzddididdd2d44x4 MD Ct ME ND ME Ae ROS RRP OR Se SS a Gar oS Ra DN LUNES LS union struct v412 captureparm capture struct v412_outputparm __ us raw_data 200 parm di IOCTL QU pcr FOR x define VIDIOC QUERYCAP _IOR define VIDIOC_RESERVED lO define VIDIOC ENUM FMT _IOWR define VIDIOC_G_FMT _IOWR define VIDIOC_S_FMT _IOWR if 1 experimental x define VIDIOC G MPEGCOMP TOR define VIDIOC_S_MPEGCOMP IOW endif define VIDIOC_REQBUFS _IOWR define VIDIOC_QUERYBUF _IOWR define VIDIOC_G_FBUF _IOR define VIDIOC_S_FBUF _IOw define VIDIOC_OVERLAY _IOW define VIDIOC_QBUF _IOWR define VIDIOC_DQBUF _IOWR define VIDIOC_STREAMON _IOw define VIDIOC STREAMOFF _IOw define VIDIOC_G_PARM _ITOWR define VIDIOC_S_PARM _ITOWR define VIDIOC_G_STD _IOR define VIDIOC_S_STD _IOW define VIDIOC_ENUMSTD _IOWR define VIDIOC_ENUMINPUT _IOWR define VIDIOC_G_CTRL _IOWR define VIDIOC_S_CTRL _IOWR define VIDIOC_G_TUNER _IOWR define VIDIOC_S_TUNER IOW define VIDIOC_G_AUDIO _IOR define VIDIOC_S_AUDIO IOW define VIDIOC_QUERYCTRL _IOWR define VIDIOC_QUERYMENU _IOWR
4. sseseseeeeseeeeeeeeeennennen entrent enne Eik Eie ETERS 80 struct VANDA PU ce oO e DRE UR Eee e rubeo er eoe IV Ee Merten 81 Input PY Pes tpe Dn Cre PRPERRPO I eR dH MER 82 Input Status Fl gs inert Dn iet ie ern eei arte eg pent 82 struct vAI2 output e oe oer Re quete quitte e Ute 84 Output Type eee oa ct reet Dai Gace e a eti e e ee irren 85 Struct VID standard te tere eter tee ther va deve eire ele e a teprE EET 86 struct v4l2 fracto ome Eunice ER DR UNES EP ele Mee ERUNT 87 typedef y4D2 Std I T sie sci ore e E 87 Video Standards based on ITU470 sess enne 88 struct v4I2 audio eet nta eeiam tenen 90 Audio Capability Flags dent erledigt Rex 91 Audio Modes 5 n david gan desee dee 91 Struct v4l2 audiooUt 3 2 stereo lette e ete cte ten eno dvo sei b Ete c cea cte eee ede ERI ape de ice ENU 92 struct V4I2 mpegs Compression etri p tede ae t bee pete ia eee eorpore 94 struct VAI2 Crop zio c UD gu RED RE ERE E E D A EEREERNT 96 irure mz PAVO 0 EPERE EEEE EA RE AEE ESE E E EE AE 97 sucet vA 2 framebuffer e ccs e cada cece rete tab tee E E ede eee sie eiie 99 Frame Butfer Capability Flags tote breite E eE E aii 100 Frame Buffer Flagge npe een d y ER Fi c ed e HE ne o e eddie 101 str ct y4l2 dormato isa Seer eee ha eee Gn RA nga 103 struct VAI frequency ioo o i ere re eerie e RED Oe tive eid 105 struct v412 jpegcompression seeeseseeeeeneeeneenen rennen nenne
5. 126 VAL2 TUN ER CAP LANG2 VAL2 TUN ER CAP SAP 0x0020 0x0020 Table 4 Tuner Audio Reception Flags VAL2 TUNI VAL2 TUNI VAL2 TUN ER SUB MONO ER SUB STEREO ER SUB LANG1 VAL2 TUN ER SUB LANG2 VAL2 TUN ER SUB SAP Table 5 Tuner Audio Modes VAL2 TUN ER MOD E MONO VAL2 TUN ER MODE 0x0001 0x0002 0x0008 0x0004 0x0004 ioctl VIDIOC G TUNER VIDIOC S TUNER Reception of the secondary language of a bilingual audio program is supported Only VA4L2 TUNER ANALOG TV tuners can have this capability Reception of a secondary audio program is supported This is a feature of the BTSC system which accompanies the NTSC video standard Two audio carriers are available for mono or stereo transmissions of a primary language and an independent third carrier for a monaural secondary language Only V4L2 TUNER ANALOG TV tuners can have this capability Note the V4L2 TUNER CAP LANG2 and VA4L2 TUNER CAP SAP flags are synonyms VAL2 TUNER CAP SAP applies when the tuner supports the V4AL2 STD NTSC M video standard The tuner receives a mono audio signal The tuner receives a stereo audio signal The tuner receives the primary language of a bilingual audio signal Drivers must clear this flag when the current video standard is VAL2 STD NTSC M The tu
6. L2 S D SECAM DK L2 S D SECAM V4L2 STD 525 60 V4L2 STD 625 50 v4 v4 L2_S1 ID UNKNOWN L2 S1 TD ALL v412 std id 0x0100 v412 std id 0x0200 lt Boa uk uk am td id re NE H H H H H H H H W NO MN PK i DON PN Qo o oonoououno UO L2 STD PAL L2 STD PAL L2 STD PAL L2 STD PAL L2 STD PAL L2 STD PAL L2 STD PAL L2 STD PAL L2 STD PAL L2 STD PAL L2 STD NTSC M L2 STD NTSC M JP I td_id 0x0001 td_id 0x0002 td_id 0x0004 0x0008 0x0010 td_id 0x0020 td_id 0x0040 td_id 0x0080 L2_STD_525_ Table 4 Video Standards based on ITU470 gt 60 L2_STD_SECAM_D L2 STD SECAM K L2 STD SECAM Kl L2 STD SECAM B L2 STD SECAM G L2 STD SECAM H L2 STD SECAM DK L2 STD SECAM IL L2 STD PAL L2 STD PAL 60 L2 STD NTSC L2 STD NTSC 443 L2 STD PAL L2 STD PAL N L2 STD PAL Nc L2 STD SECAM L2 STD 625 50 ioctl VIDIOC ENUMSTD 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 a Pd Pas 88 ioctl VIDIOC ENUMSTD CharacteristicM PAL N PAL B B1 D D1 H PAL I PAL B D M NTSC G PAL K PAL G SECAWBECAM SEQASECAM Frame 525 lines Frame 1001 30000 period s Chrominance 4433618 75 5 sub 3579545357961 14493618 75 4433618 75 carrier 10 10 5 1 fre 3582056 25 quency 5 Hz INominal 6 6 6 B 7 8 8 8 8 8
7. See Table 4 gt Set by drivers and applications see Table 5 gt This is is the desired period between successive frames captured by the driver in seconds The field is intended to skip frames on the driver side saving I O bandwidth Applications store here the desired frame period drivers return the actual frame period which must be greater or equal to the nominal frame period determined by the current video standard struct v412 standard rameperiod field Changing the video standard also implicitly by switching the video input may reset this parameter to the nominal frame period To reset manually applications can just set this field to Zero Drivers support this function only when they set the V4AL2 CAP TIMEPERFRAME flag in the capability field Custom driver specific streaming parameters When unused applications and drivers must set this field to zero Applications using this field should check the driver name and version see Section 1 2 Applications set this field to the desired number of buffers used internally by the driver in read mode Drivers return the actual number of buffers When an application requests zero buffers drivers should just return the current setting rather than the minimum or an error code For details see Section 3 1 Reserved for future extensions Drivers and applications must set the array to zero 117 u32 capability u32 outputmode struct v412
8. V4L2_CID_VCEN V4L2_CID_LASTP1 V4L2_CID_PRIVAT ER ER E BAS Type boolean integer boolean button integer integer integer integer integer boolean integer boolean boolean integer integer Chapter 1 Common API Elements Description Loudness mode bass boost Another name for brightness not a synonym of V4L2_CID_BRIGHTNESS Automatic white balance cameras This is an action control When set the value is ignored the device will do a white balance and then hold the current setting Contrast this with the boolean V4L2 CID AUTO WHITE BALANCE which when activated keeps adjusting the white balance Red chroma balance Blue chroma balance Gamma adjust Whiteness for grey scale devices This is a synonym for V4AL2 CID GAMMA Exposure cameras Unit Automatic gain exposure control Gain control Mirror the picture horizontally Mirror the picture vertically Horizontal image centering Vertical image centering Centering is intended to physically adjust cameras For image cropping see Section 1 10 for clipping Section 4 2 End of the predefined control IDs currently V4L2_CID_VCENTER 1 ID of the first custom driver specific control Applications depending on particular custom controls should check the driver name and version see Section 1 2 gt Applications can enumerate the available controls with
9. request VIDIOC ENUMAUDOUT argp Description To query the attributes of an audio output applications initialize the index field and zero out the reserved array of a struct v412_audioout and call the VIDIOC_G_AUDOUT ioctl with a pointer to this structure Drivers fill the rest of the structure or return an EINVAL error code when the index is out of bounds To enumerate all audio outputs applications shall begin at index zero incrementing by one until the driver returns EINVAL Note connectors on a TV card to loop back the received audio signal to a sound card are not audio outputs in this sense See ioctl VIDIOC G AUDOUT VIDIOC 5 AUDOUT 2 for a description of struct v412_audioout Return Value On success 0 is returned on error 1 and the errno variable is set appropriately EINVAL The number of the audio output is out of bounds or there are no audio outputs at all and this ioctl is not supported 78 ioctl VIDIOC ENUM FMT Name VIDIOC ENUM FMT Enumerate image formats Synopsis int ioctl int fd int request struct v412 fmtdesc xargp Arguments fd File descriptor returned by open request VIDIOC ENUM FMT argp Description To enumerate image formats applications initialize the t ype and index field of struct v412 fmtdesc and call the VIDIOC_ENUM_FMT ioctl with a pointer to this structure Drivers fill the rest of the structure or return an EINVAL error code All formats are enumer
10. ELD NONE VAL2 FII I VAL2 FII I D TOP D BOTTOM VAL2 FI ELD INTERLACED VAL2 FI ELD S EO TB VAL2 FI ELD S EQ BT ELD ANY 0 Applications request this field order when any one of the VAL2 FIELD NONE VA4L2 FIELD TOP VAL2 FIELD BOTTOM or VA4L2 FIELD INTERLACED formats is acceptable Drivers choose depending on hardware capabilities or e g the requested image size and return the actual field order struct v412 buffer field can never be VAL2 FIELD ANY Images are in progressive format not interlaced The driver may also indicate this order when it cannot distinguish between V4L2 FIELD TOP and V4L2 FIELD BOTTOM Images consist of the top field only Images consist of the bottom field only Applications may wish to prevent a device from capturing interlaced images because they will have comb or feathering artefacts around moving objects Images contain both fields interleaved line by line The temporal order of the fields whether the top or bottom field is first transmitted depends on the current video standard M NTSC transmits the bottom field first all other standards the top field first Images contain both fields the top field lines are stored first in memory immediately followed by the bottom field lines Fields are always stored in temporal order the old
11. Chapter 3 Input Output USB cameras Here timestamps refer to the instant the field or frame was received by the driver not the capture time These devices identify by not enumerating any video standards see Section 1 7 Similar limitations apply to output timestamps Typically the video hardware locks to a clock controlling the video timing the horizontal and vertical synchronization pulses At some point in the line sequence possibly the vertical blanking an interrupt routine samples the system clock compares against the timestamp and programs the hardware to repeat the previous field or frame or to display the buffer contents Apart of limitations of the video device and natural inaccuracies of all clocks it should be noted system time itself is not perfectly stable It can be affected by power saving cycles warped to insert leap seconds or even turned back or forth by the system administrator affecting long term measurements Table 3 1 struct v412 buffer u32 index Number of the buffer set by the application This field is only used for memory mapping I O and can range from zero to the number of buffers allocated with the VIDIOC_REQBUFS ioctl struct v412_requestbuffers count minus one enum v412_buf_typet ype Type of the buffer same as struct v412_format type or struct v412_requestbuffers type set by the application u32 bytesused The number of bytes occupied by the data in the buffer It depends on th
12. const char x unsigned long oblock int noblock unsigned int poll struct video device struct file poll table x int xioctl struct video device x unsigned int void x int xmmap struct video device const char unsigned long int xinitialize struct video device gt fendif fif OBSOLETE OWNER x to be removed in 2 6 15 x obsolet fops owner is used instead struct module owner dev driver data will be used instead some day x Use the video get set drvdata helper functions so the switch over will be transparent for you x Or use pcilusb _ get set _drvdata directly void xpriv fendif for videodev c intenal usage please don t touch int users video exclusive open close struct semaphore lock helper function uses these if LINUX VERSION CODE lt KERNEL VERSION 2 5 69 devfs handle t devfs handle devfs x else char devfs_name 64 x devfs x endif if LINUX VERSION CODE gt KERNEL VERSION 2 6 0 struct class device class dev sysfs endif 180 Appendix A Video For Linux Two Header File define VIDEO MAJOR 81 extern int video register device struct video device x int type int nr extern void video unregister device struct video device x extern int video usercopy struct inode xinode struct file file unsi
13. M 147 VAL2Z MUNMAP 149 VAL OPEN vossccsscsssccsccveecsvsservonsssascoss sceseseveccsseedsecscsasoeassacescasesuebexcossssteovassbesustee sendesedsesseseseassscossdeeee 150 VAZ POM Um E secs 152 WALD VIDI COUR 153 b BUTS Tre 155 VAUD Sici T E 156 V4L2 close Name v412 close Close a V4L2 device Synopsis include lt unistd h gt int close int fd Arguments fd File descriptor returned by open Description Closes the device Any I O in progress is terminated and resources associated with the file descriptor are freed However data format parameters current input or output control values or other properties remain unchanged Return Value The function returns 0 on success 1 on failure and the errno is set appropriately Possible error codes EBADF dis not a valid open file descriptor 72 V4L2 ioctl Name v412 ioctl Program a V4L2 device Synopsis include sys ioctl h int ioctl int fd int request void xargp Arguments fd File descriptor returned by open request VAL2 ioctl request code as defined in the videodev h header file for example VIDIOC QUERYCAP argp Pointer to a function parameter usually a structure Description The ioct1 function is used to program V4L2 devices The argument d must be an open file descriptor An i
14. The norm field describing the supported video standards was replaced by sta The VAL specification mentions a flag VIDEO VC NORM indicating whether the standard can be changed This flag was a later addition together with the norm field and has been removed in the meantime V4L2 has a similar albeit more comprehensive approach to video standards see Section 1 7 for more information 161 Chapter 6 History 6 1 4 Tuning The VAL VIDIOCGTUNER and VIDIOCSTUNER ioctl and struct video tuner can be used to enumerate the tuners of a VAL TV or radio device The equivalent V4L2 ioctls are vIDIOC G TUNER and VIDIOC S TUNER using struct v4I2 tuner Tuners are covered in Section 1 6 The tuner field counting tuners was renamed to index The fields name rangelow and rangehigh remained unchanged The VIDEO TUNER PAL VIDEO TUNER NTSC and VIDEO TUNER SECAM flags indicating the supported video standards were dropped This information is now contained in the associated struct v4I2 input No replacement exists for the VIDEO TUNER NORM flag indicating whether the video standard can be switched The mode field to select a different video standard was replaced by a whole new set of ioctls and structures described in Section 1 7 Due to its ubiquity it should be mentioned the BTTV driver supports several standards in addition to the regular VIDEO MODE PAL 0 VIDEO MODE NTSC VIDEO MODE SECAM and VIDEO MO
15. V4L2 INPUT TYPE TUNER this is an RF connector and this field identifies the tuner It corresponds to struct v412 tuner field index For details on tuners see Section 1 6 Every video input supports one or more different video standards This field is a set of all supported standards For details on video standards and how to switch see Section 1 7 This field provides status information about the input See Table 3 for flags status is only valid when this is the current input Reserved for future extensions Drivers must set the array to zero u32 audioset u32 tuner v412 std id std u32 status u32 reserved 4 Table 2 Input Types VA4L2 INPUT TYPE TUNER V4L2 INPUT TYPE CAMERA 2 Table 3 Input Status Flags General VA4L2 IN ST NO POWER VA4L2 IN ST NO SIGNAL V4L2 IN ST NO COLOR Analog Video VA4L2 IN ST NO H LOCK V4L2 IN ST COLOR KILL This input uses a tuner RF demodulator Analog baseband input for example CVBS Composite Video S Video RGB 0x00000001 0x00000002 0x00000004 0x00000100 0x00000200 Attached device is off The hardware supports color decoding but does not detect color modulation in the signal No horizontal sync lock A color killer circuit automatically disables color decoding when it detects no color modulation When this flag is set the color killer is enabled and has shut off color decoding 82 Digital Vi
16. return 0 case EIO Could ignore EIO see spec fall through x default errno exit read process image buffers 0 start break case IO METHOD MMAP CLEAR buf Em buf type VA4L2 BUF TYPE VIDEO CAPTURE buf memory V4L2 MEMORY MMAP if 1 xioctl fd VIDIOC DOBUF amp buf 201 Appendix B Video Capture Example switch errno case EAGAIN return 0 case EIO Could ignore EIO see spec fall through default errno exit VIDIOC DQBUF assert buf index n buffers process image buffers buf index start if 1 xioctl fd VIDIOC QBUF amp buf errno exit VIDIOC QBUF break case IO METHOD USERPTR CLEAR buf buf type VA4L2 BUF TYPE VIDEO CAPTURE buf memory V4L2 MEMORY USERPTR Em if 1 xioctl fd VIDIOC DOBUF amp buf switch errno case EAGAIN return 0 case EIO Could ignore EIO see spec fall through default errno exit VIDIOC DQBUF for i 0 i lt n buffers i if buf m userptr unsigned long buffers i start amp amp buf length buffers i length break assert i lt n_buffers process image void buf m userptr if 1 xioctl fd VIDIOC_QBUF amp buf errno exit VIDIOC QBUF break 202 return 1 static void Appendix B
17. volume VAL2 CID AUDIO VOLUME bass V4L2_CID_AUDIO_BASS treble V4L2_CID_AUDIO_TREBLE balance V4L2_CID_AUDIO_BALANCE 163 Chapter 6 History To determine which of these controls are supported by a driver VAL provides the 1ags VIDEO AUDIO VOLUME VIDEO AUDIO BASS VIDEO AUDIO TREBLE and VIDEO AUDIO BALANCE In the V4L2 API the VIDIOC QUERYCTRL ioctl reports if the respective control is supported Accordingly the vIDEO AUDIO MUTABLE and VIDEO AUDIO MUTE flags where replaced by the boolean V4L2 CID AUDIO MUTE control All V4L2 controls have a step attribute replacing the struct video audio step field The V4L audio controls are assumed to range from 0 to 65535 with no particular reset value The V4L2 API permits arbitrary limits and defaults which can be queried with the VIDIOC_QUERYCTRL ioctl For general information about controls see Section 1 8 6 1 7 Frame Buffer Overlay The V4L2 ioctls equivalent to VIDIOCGFBUF and VIDIOCSFBUF are VIDIOC G FBUF and VIDIOC S FBUF The base field of struct video buffer remained unchanged except V4L2 using a flag to indicate non destructive overlay instead of a NULL pointer All other fields moved into the struct v4I2 pix format substructure fmt of struct v412 framebuffer The depth field was replaced by pixelformat A conversion table is available in the Section 2 3 Instead of the special ioctls VIDIOCGWIN and VIDIOCSWIN V4L2 uses the
18. while 0 ioctl fd VIDIOC ENUMSTD amp standard if standard id amp std_id printf Current video standard s n standard name exit EXIT_SUCCESS standard indext EINVAL indicates the end of the enumeration which cannot be empty unless this device falls under the USB exception x if errno EINVAL standard index 0 perror VIDIOC_ENUMSTD exit EXIT_FAILURE Example 1 6 Listing the video standards supported by the current input struct v412 input input struct v412 standard standard memset amp input 0 sizeof input if 1 ioctl fd VIDIOC G INPUT amp input index perror VIDIOC G INPUT exit EXIT FAILURE if 1 ioctl fd VIDIOC ENUMINPUT amp input perror VIDIOC ENUM INPUT exit EXIT FAILURE T Chapter 1 Common API Elements printf Current input s supports Mn input name memset amp standard 0 sizeof standargad standard index 0 while 0 ioctl fd VIDIOC ENUMSTD amp standard if standard id amp input std printf Ss n standard name standard indext EINVAL indicates the end of the enumeration which cannot be empty unless this device falls under the USB exception x if errno EINVAL standard index 0 perror VIDIOC_ENUMSTD exit EXIT_FAILURE Example 1 7 Selecting a new video standard
19. Chapter 6 History multiple groups within a category Controls within a group would typically be drawn within a group box Controls in different categories might have a greater separation or even be in separate windows 1 The v4I2 buffer timestamp field is changed to a 64 bit integer and holds the time of the frame based on the system time in 1 nanosecond units Additionally timestamps will be in absolute system time not starting from zero at the beginning of a stream as it is now The data type name for timestamps is stamp t defined as a signed 64 bit integer Output devices should not send a buffer out until the time in the timestamp field has arrived I would like to follow SGI s lead and adopt a multimedia timestamping system like their UST Unadjusted System Time See http reality sgi com cpirazzi_engr lg time intro html This link is no longer valid UST uses timestamps that are 64 bit signed integers not struct timeval s and given in nanosecond units The UST clock starts at zero when the system is booted and runs continuously and uniformly It takes a little over 292 years for UST to overflow There is no way to set the UST clock The regular Linux time of day clock can be changed periodically which would cause errors if it were being used for timestamping a multimedia stream A real UST style clock will require some support in the kernel that is not there yet But in anticipation I will change the timestamp field to a 64
20. VIDIOC REQBUFS or when the device is closed Applications must take care not to free buffers without dequeuing For once the buffers remain locked until further wasting physical memory Second the driver will not be notified when the memory is returned to the application s free list and subsequently reused for other purposes possibly completing the requested DMA and overwriting valuable data For capturing applications it is customary to enqueue a number of empty buffers to start capturing and enter the read loop Here the application waits until a filled buffer can be dequeued and re enqueues the buffer when the data is no longer needed Output applications fill and enqueue buffers when enough buffers are stacked up output is started In the write loop when the application runs out of free buffers it must wait until an empty buffer can be dequeued and reused Two methods exist to suspend execution of the application until one or more buffers can be dequeued By default VIDIOC_DQBUF blocks when no buffer is in the outgoing queue When the O_NONBLOCK flag was given to the open function VIDIOC DOBUF returns immediately with an EAGAIN error code when no buffer is available The select or po11 function are always available To start and stop capturing or output applications call the VIDIOC_STREAMON and VIDIOC STREAMOFF ioctl Note VIDIOC STREAMOFF removes all buffers from both queues and unlocks all buffers as a side effect Since the
21. When reading or writing is supported the driver must also support the select and poll function 3 2 Streaming I O Memory Mapping Input and output devices support this I O method when the v4L2_CAP_STREAMING flag in the capabilities field of struct v412 capability returned by the VIDIOC_QUERYCAP ioctl is set There 37 Chapter 3 Input Output are two streaming methods to determine if the memory mapping flavor is supported applications must call the VIDIOC_REQBUFS ioctl Streaming is an I O method where only pointers to buffers are exchanged between application and driver the data itself is not copied Memory mapping is primarily intended to map buffers in device memory into the application s address space Device memory can be for example the video memory on a graphics card with a video capture add on However being the most efficient I O method available for a long time many other drivers support streaming as well allocating buffers in DMA able main memory A driver can support many sets of buffers Each set is identified by a unique buffer type value The sets are independent and each set can hold a different type of data To access different sets at the same time different file descriptors must be used To allocate device buffers applications call the VIDIOC_REQBUFS ioctl with the desired number of buffers and buffer type for example V4L2 BUF TYPE VIDEO CAPTURE This ioctl can also be used to change the number of
22. all requests and always returns default parameters as VIDIOC G FMT does VIDIOC TRY FMT is optional 4 3 4 Writing Images A video output device may support the write function and or streaming memory mapping or user pointer I O See Chapter 3 gt for details 4 4 Codec Interface Suspended This interface has been be suspended from the V4L2 API implemented in Linux 2 6 until we have more experience with codec device interfaces A VAL2 codec can compress decompress transform or otherwise convert video data from one format into another format in memory Applications send data to be converted to the driver through the write call and receive the converted data through the read call For efficiency a driver may also support streaming I O to do 56 Chapter 4 Device Types 4 5 Effect Devices Interface Suspended This interface has been be suspended from the V4L2 API implemented in Linux 2 6 until we have more experience with effect device interfaces A VAL2 video effect device can do image effects filtering or combine two or more images or image streams For example video transitions or wipes Applications send data to be processed and receive the result data either with read and write functions or through the streaming I O mechanism to do 4 6 Raw VBI Data Interface VBl is an abbreviation of Vertical Blanking Interval a gap in the sequence of lines of an analog video signal During VBI no picture
23. define VIDIOC_G_INPUT _IOR define VIDIOC_S_INPUT _IOWR define VIDIOC_G_OUTPUT _IOR define VIDIOC_S_OUTPUT _ITOWR define VIDIOC_ENUMOUTPUT _IOWR define VIDIOC_G_AUDOUT _IOR define VIDIOC_S_AUDOUT _IOW lt i 50 O Dog VTCC ES struct v412 capability struct v412 fmtdesc struct v412 format struct v412 format struct v412 mpeg compression struct v412 mpeg compression struct v412 requestbuffers struct v412 buffer struct v412 framebuffer struct v412 framebuffer int struct v412 buffer struct v412 buffer int int struct v412 streamparm struct v412 streamparm v412 std id v412 std id struct v412 standard struct v412 input struct v412 control struct v412 control struct v412 tuner struct v412 tuner struct v412 audio struct v412 audio struct v412 queryctrl struct v412 querymenu int int int int struct v412 output struct v412 audioout struct v412 audioout 197 Appendix A Video For Linux Two Header File define VIDIOC G MODULATOR _IOWR V 54 struct v412 modulator define VIDIOC S MODULATOR _IOw V 55 struct v412 modulator define VIDIOC G FREQUENCY _IOWR V 56 struct v412 frequency define VIDIOC S FREQUENCY _IOw V 57 struct v412 frequency define VIDIOC CROPCAP _IOWR V 58 struct v412 cropc
24. gt function was incorrect 2 Audio output ioctls end in AUDOUT not AUDIOOUT 3 In the current audio input example the vIDIOC G AUDIO ioctl took the wrong argument 4 The VIDIOC_QBUF and VIDIOC DOBUF ioctl did not mention the struct v412 buffer memory field it was also missing from examples Added description of the VIDIOC_DQBUF EIO error 176 Chapter 6 History 6 2 15 V4L2 in Linux 2 6 14 1 A new sliced VBI interface see Section 4 7 was added It replaces the interface proposed in VAL2 specification 0 8 6 2 16 V4L2 in Linux 2 6 15 1 The viDIOC LOG STATUS ioctl was added 2 New video standards V4L2 STD NTSC 443 VAL2 STD SECAM LC VAL2 STD SECAM DK a set of SECAM D K and K1 and VAL2 STD ATSC a set of VAL2 STD ATSC 8 VSB and V4L2 STD ATSC 16 VSB were defined Note the vVAL2 STD 525 60 set now includes VA4L2 STD NTSC 443 See also Table 3 3 The vibiOC G coMP and VIDIOC S COMP ioctl were renamed to VIDIOC G MPEGCOMP and VIDIOC S MPEGCOMP respectively Their argument was replaced by a struct v412 mpeg compression pointer 6 2 17 VAL2 spec erratum 2005 11 27 The capture example in Appendix B called vVIDIOC_S_CROP without checking if cropping VIDIOC_CROPCAP is supported In the video standard selection example in Section 1 7 the VIDIOC S STD call used the wrong argument type 6 2 18 VAL2 spec erratum 2006 01 10 1 The V4AL2 IN ST COLOR KILL flag in
25. ifndef define ifdef 3E endif if endif endif Common stuff for both V4L1 and V4L2 LINUX VID LINUX VID EOD EV2 H EOD EV2 H Video for Linux Two Header file for v4l or V4L2 drivers and applications Linux kernels 2 2 x or 2 4 x for See http bytesex org v41 for API specs and other v412 documentation Author K include linux time h need struct timeval include linux poll LINUX VERSION COD include 1 LINUX VERSION COD linux device h include lt include lt define OBSOL define HAVE V4 et al ERNEL Bill Dirks bdir Justin Schoeman h gt inux devfs E KERNE fs kernel ET a L E gt KERNE x Moved from videodev h define define define define define define define define define define define define define define define ifdef VI VI MI VI VI VI VI VI VI VI VI VI VI VI VID _ K K U EFE a gt Fo 4 pr Q U T U ES E ea hay es Q E D z E T ER UU UU UUUIUIUIUuUuuuUu H HS HN HS FH FN FH FH oH FH oH KK ER ERNEL BON A 32 64 128 256 912 1024 2048 4096 8192 32
26. sizeof buffers assert buffers NULL for i 0 i reqbuf count i struct v412 buffer buffer memset amp buffer 0 sizeof buffer buffer type regqbuf type buffer memory V4L2_MEMORY_MMAP buffer index i if 1 ioctl fd VIDIOC QUERYBUF amp buffer perror VIDIOC QUERYBUF exit EXIT FAILURE buffers i length buffer length x remember for munmap x buffers i start mmap NULL buffer length PROT READ PROT WRITE x required x MAP SHARED recommended fd buffer m offset if buffers i start MAP FAILED You may need to unmap and free the so far mapped buffers here perror mmap exit EXIT FAILURE Cleanup for i 0 i reqbuf count itt munmap buffers i start buffers i length Streaming drivers maintain two buffer queues an incoming and an outgoing queue They separate the synchronous capture or output operation locked to a video clock from the application which is subject to random disk or network delays and preemption by other processes thereby reducing the probability of data loss The queues are organized as FIFOs buffers will be output in the order enqueued in the incoming FIFO and were captured in the order dequeued from the outgoing FIFO The driver may require a minimum number of buffers enqueued at all times to function apart of this no limit exists on the number
27. the last channel as Second Audio Program When the input has only one channel it is used for both audio tracks When the input has three channels the mono track is a down mix of channel 1 and 2 When combined with V4L2 TUNER SUB STEREO channel 1 and 2 are encoded as left and right stereo audio channel 3 as Second Audio Program When the input has only two channels the first is encoded as left and right channel and the second as SAP When the input has only one channel it is used for all audio tracks It is not possible to encode a Second Audio Program only This flag must combine with V4L2 TUNER SUB MONO or V4L2 TUNER SUB STEREO If the hardware does not support the respective audio matrix or the current video standard does not permit SAP the VIDIOC S MODULATOR ioctl shall return an EINVAL error code and driver shall fall back to mono or stereo mode On success 0 is returned on error 1 and the errno variable is set appropriately EINVAL The struct v412 modulator index is out of bounds 113 ioctl VIDIOC G OUTPUT VIDIOC S OUTPUT Name VIDIOC G OUTPUT VIDIOC S OUTPUT Query or select the current video output Synopsis int ioctl int fd int request int xargp Arguments fd File descriptor returned by open request VIDIOC G OUTPUT VIDIOC S OUTPUT argp Description To query the current video output applications call the VIDIOC_G_OUTPUT ioctl with a pointe
28. 1 in either direction and the image size must be a multiple of 16 x 16 pixels The cropping rectangle be set to the upper limit 640 x 400 pixels at offset 0 0 Let a video capture application request an image size of 300 x 225 pixels assuming video will be scaled down from the full picture accordingly The driver will set the image size to the closest possible values 304 x 224 then choose the cropping rectangle closest to the requested size that is 608 x 224 224 x 2 1 would exceed the limit 400 The offset 0 O is still valid thus unmodified Given the default cropping rectangle reported by VIDIOC_CROPCAP the application can easily propose another offset to center the cropping rectangle Now the application may insist on covering an area using an aspect closer to the original request Sheepish it asks for a cropping rectangle of 608 x 456 pixels The present scaling factors limit cropping to 640 x 384 so the driver returns the cropping size 608 x 384 and accordingly adjusts the image size to 304 x 192 Eventually some crop or scale parameters are locked for example when the driver supports simultaneous video capturing and overlay another application already started overlay and the cropping parameters cannot be changed anymore Also VIDIOC TRY FMT cannot change the cropping rectangle In these cases the driver has to approach the closest values possible without adjusting the opposite rectangle The struct v412 cropcap which also reports the
29. FIELD SEQ TB N field V4L2 FIELD SEQ BT define V4L2 FIELD HAS BOTTOM field 9 field V4L2_FIELD_BOTTOM field V4L2_FIELD_INTERLACED field V4L2_FIELD_SEQ_TB field V4L2_FIELD_SEQ_BT define V4L2_FIELD_HAS_BOTH field N field V4L2 FIELD INTERLACED field V4L2_FIELD_SEQ_TB LIN field V4L2 FIELD SEQ BT 181 enum v412 buf L2 L2 L2 L2 L2 v4 v4 v4 v4 v4 type w UE YPE VIDEO_CAPT URE UJ YP VIDEO OUTP UJ YP VIDEO OVER UT AY UJ YP VBI_CAPT Hj Hj Hj hj UJ YPE VBI OUTPUT if 1 KE av x v4 endif V4L2_B HH L2 B VA4AL2 B UE YPE IC URI m Experimental Sliced VBI ED VBI CAPTURE UE YPE iLC ED_VBI_OUTPUT F_TYP enum v412 ctrl type v4 RIVATE RL_TYPE ER VAL2 RL TYPE EAN VAL2 RL TYPE v4 RL_TYPE F enum v412 tuner v4 type UN v4 a y ER RAD UN IO ER ANALOG TV v4 i2 TUN F enum v412 memory v4 zj 12 v4 i2 zj ORY_US v4 12 zj H see also ht tp vek enum v412 colorspace v4 IT 2 COLORSPAC ER DIGITAL TV ORY MMAP
30. License under the terms defined in section 4 above for modified versions provided that you include in the combination all of the Invariant Sections of all of the original documents unmodified and list them all as Invariant Sections of your combined work in its license notice The combined work need only contain one copy of this License and multiple identical Invariant Sections may be replaced with a single copy If there are multiple Invariant Sections with the same name but different contents make the title of each such section unique by adding at the end of it in parentheses the name of the original author or publisher of that section if known or else a unique number Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work In the combination you must combine any sections entitled History in the various original documents forming one section entitled History likewise combine any sections entitled Acknowledgements and any sections entitled Dedications You must delete all sections entitled Endorsements C 7 6 COLLECTIONS OF DOCUMENTS You may make a collection consisting of the Document and other documents released under this License and replace the individual copies of this License in the various documents with a single 215 Appendix C GNU Free Documentation License copy that is included in the collection provided that you follow th
31. Telecommunication Standards Institute http www etsi org ETS 300 706 Enhanced Teletext specification VAL Alan Cox Video4Linux API Specification This file is part of the Linux kernel sources under Documentation video4linux VALPROG Alan Cox Video4Linux Programming a k a The Video4Linux Book 2000 About VAL driver programming This book is part of the Linux kernel DocBook documentation for example at http kernelnewbies org documents SGML sources are included in the kernel sources VPS European Telecommunication Standards Institute http www etsi org ETS 300 231 Specification of the domestic video Programme Delivery Control system PDC WSS International Telecommunication Union http www itu ch European Telecommunication Standards Institute http www etsi org ITU R Recommendation BT 1119 EN 300 294 625 line television Wide Screen Signalling WSS 218
32. The V4L2 API permits arbitrary limits and defaults which can be queried with the VIDIOC_QUERYCTRL ioctl For general information about controls see Section 1 85 The depth average number of bits per pixel of a video image is implied by the selected image format V4L2 does not explicitely provide such information assuming applications recognizing the format are aware of the image depth and others need not know The palette field moved into the struct v412 pix format 162 Chapter 6 History struct video picture pa1ette struct v4I2 pix format pixfmt VIDEO PALETTE GREY VA4L2 PIX FMT GREY VIDEO PALETTE HI240 VAL2 PIX FMT HI240a VIDEO PALETTE RGB565 VA4L2 PIX FMT RGB565 VIDEO PALETTE RGB555 VA4L2 PIX FMT RGB555 VIDEO PALETTE RGB24 VA4L2 PIX FMT BGR24 VIDEO PALETTE RGB32 VA4L2 PIX FMT BGR32 VIDEO PALETTE YUV422 VAL2 PIX FMT YUYV VIDEO PALETTE YUYVc VAL2 PIX FMT YUYV VIDEO PALETTE UYVY VA4L2 PIX FMT UYVY VIDEO PALETTE YUV420 None VIDEO_PALETTE_YUV411 V4L2_PIX_FMT_Y41Pa VIDEO PALETTE RAW INone e VIDEO PALETTE YUV422P VAL2 PIX FMT YUV422P VIDEO PALETTE YUV411P V4L2_PIX_FMT_YUV411Pr VIDEO PALETTE YUV420P VAL2 PIX FMT YVU420 VIDEO PALETTE YUV410P VAL2 PIX FMT YVU410 Notes a This is a custom format used by the BTTV
33. Use application allocated buffers Mn um argv 0 static const char short options d hmru static const struct option long_options device required_argument NULL Ds NM help no argument NULL HY mmap no_argument NULL mt read no argument NULL A 45 userp no argument NULL TISA ds P 05 Dy OF int main int argc char argv dev name dev video for int index gc c c getopt long argc argv short_options long_options amp index if 1 c break 210 switch case 0 Appendix B Video Capture Example c getopt long flag break case d case h case m case r case u dev name optarg break Tos usage stdout argc argv exit EXIT SUCCESS io IO METHOD MMAP io IO METHOD READ io IO METHOD USERPTR break default open device init device start capturing mainloop usage stderr argc argv exit EXIT FAILURE stop capturing uninit device close device exit EXIT SUCCESS return 0 211 Appendix C GNU Free Documentation License C 1 0 PREAMBLE The purpose of this License is to make a manual textbook or other written document free in the sense of freedom to assure everyone the effective freedom to copy and redistribute it with or without modifying it either comm
34. V4 define define v4 v4 L2 L2 S L2 S ID NTSC D SECAM DK L2 S L2 S1 SECAM V4L2 STD 525 60 V4L2 STD 625 50 ID ATSC ID UNKNOWN L2 S1 TD ALL struct v412 standard v412 std id struct v412 fract u32 u8 u32 u32 hi VID x ti O struct v412 input Appendix A Video For Linux Two Header File V4L2_STD_NTSC_M V4L2_STD_NTSC_M_JP V4L2_STD_SECAM_D V4L2_STD_SECAM_K V4L2_STD_SECAM_K1 V4L2_STD_SECAM_B V4L2_STD_SECAM_ M V4L2 STD SECAM H N VA4L2 STD SECAM DK N V4L2 STD SECAM L VAL2 STD PAL N VA4L2 STD PAL 60 N VA4L2 STD NTSC N V4L2 STD NTSC 443 VAL2 STD PAL N V4L2 STD PAL N N VA4L2 STD PAL Nc N V4L2 STD SECAM VAL2 STD ATSC 8 VSB N V4L2 STD ATSC 16 VSB 0 VAL2 STD 525 60 IN V4L2 STD 625 50 index id name 24 frameperiod x Frames framelines reserved 4 LNP UTS not fields x bitfield u32 index Which input x u8 name 32 Label _ u32 type Type of input u32 audioset Associated audios u32 tuner Associated tuner v4l12 std id std u32 status 32 reserved 4 i Values for the type field define V4L2 INPUT TYPE TUNER al define V4L2_INPUT_TYPE_CAMERA 2 field status define VA4L2 IN ST NO POW ER general x 0x000000
35. V4L2_CID_AUTO_WHITE_BALANCE V4L2_CID_BASE define V4L2_CID_DO_WHITE_BALANCE V4L2_CID_BASE define V4L2_CID_RED_BALANCE V4L2_CID_BASE define V4L2_CID_BLUE_BALANCE V4L2_CID_BASE define V4L2_CID_GAMMA V4L2_CID_BASE define V4L2_CID_WHITENESS V4L2_CID_GA define V4L2_CID_EXPOSURE V4L2_CID_BASE define V4L2_CID_AUTOGAIN V4L2_CID_BASE define V4L2_CID_GAIN V4L2_CID_BASE define V4L2_CID_HFLIP V4L2_CID_BASE define V4L2_CID_VFLIP V4L2_CID_BASE define V4L2_CID_HCENTER V4L2_CID_BASE define V4L2_CID_VCENTER V4L2_CID_BASE define V4L2_CID_LASTP1 V4L2_CID_BASE x TUNING struct v412 tuner 132 index u8 name 32 enum v412 tuner type type u32 capability u32 rangelow u32 rangehigh u32 rxsubchans 000 1001 WBN P C GG a Go Noe SS SS M a dut E Se SO t t t t t oon 20 21 22 23 24 ENU ioctl for querying menu items x Not sure last CID 1 193 c 1032 7932 29532 u32 E Appendix A Video For Linux Two Header File audmode signal afc reserved 4 struct v412_modulator u32 u8 u32 u32 u32 u32 32 Flags for index name 32 capability rangelow rangehigh txsubchans reserved 4 the capability field define V4L2 define V4L2 define V4L2 define V4L2_ define V4L2_ define V4L2 TUNER CAP LOW 0x0001 TU
36. VAI2 queryctrl ete ben tento been tet 138 struct v4I2 querymendu 5 2 oct e e et E t Ic re e Ie Ue agi 139 en m v4I2 ctrl type ote ra mU RATER ET REESE NO TOR RR 139 Control Flags eet o emet e ee eb deles tte 140 struct vAI2 requestbuffers oso e quete eti sete rte egi 143 6 1 V4L Device Types Names and Numbers essere 159 viii Introduction to do If you have questions or ideas regarding the API please try the Video4Linux mailing list https listman redhat com mailman listinfo video4linux list For documentation related requests contact the maintainer at mschimek gmx at mailto mschimek gmx at The latest version of this document and the DocBook SGML sources is currently hosted at http v4l2spec bytesex org and http linuxtv org downloads video4linux API V4L2_API Chapter 1 Common API Elements Programming a V4L2 device consists of these steps Opening the device Changing device properties selecting a video and audio input video standard picture brightness a o Negotiating a data format Negotiating an input output method The actual input output loop Closing the device In practice most steps are optional and can be executed out of order It depends on the V4L2 device type you can read about the details in Chapter 4 gt In this chapter we will discuss the basic concepts applicable to all devices 1 1 Opening and Closing Devices 1 1 1 Device Naming V
37. Version number of the driver Together with the driver field this identifies a particular driver The version number is formatted using the KERNEL_VERSION macro Device capabilities see Table 2 gt this array to zero Reserved for future extensions Drivers must set 0x00000001 The device supports the video capture interface 0x00000002 The device supports the video output interface 0x00000004 The device supports the video overlay interface Overlay typically stores captured images directly in the video memory of a graphics card with support for clipping 0x00000010 The device supports the VBI capture interface Section 4 6 Section 4 7 see 0x00000020 The device supports the VBI output interface see Section 4 6 Section 4 7 0x00000100 to be defined 0x00010000 The device has some sort of tuner or modulator to receive or emit RF modulated video signals For more information see Section 1 62 136 KE RNE LL ioctl VIDIOC QUERYCAP V4L2 CAP AUDIO 0x00020000 The device has audio inputs or outputs For more information see Section 1 5 It may or may not support PCM sampling or output this function must be implemented as ALSA or OSS PCM interface V4L2 CAP READWRITE 0x01000000 The device supports the read and or write I O methods V4L2 CAP ASYNCIO 0x02000000 The device supports the asynchronous I O methods V4L2 CAP STREAMING 0x04000
38. When set frame numbers 0 and 1 at the start of each minute except minutes 0 10 20 30 40 50 are omitted from the count V4L2 TC FLAG COLORFRAME 0x0002 The color frame flag VA4L2 TC USERBITS field 0x000C Field mask for the binary group flags V4L2 TC USERBITS USERDEFINEDOx0000 Unspecified format VA4L2 TC USERBITS 8BITCHARS 0x0008 8 bit ISO characters 3 6 Field Order We have to distinguish between progressive and interlaced video Progressive video transmits all lines of a video image sequentially Interlaced video divides an image into two fields containing only the odd and even lines of the image respectively Alternating the so called odd and even field are transmitted and due to a small delay between fields a cathode ray TV displays the lines interleaved yielding the original frame This curious technique was invented because at refresh rates similar to film the image would fade out too quickly Transmitting fields reduces the flicker without the necessity of doubling the frame rate and with it the bandwidth required for each channel It is important to understand a video camera does not expose one frame at a time merely transmitting the frames separated into fields The fields are in fact captured at two different instances in time An object on screen may well move between one field and the next For applications analysing motion it is of paramount importance to recognize which field of a frame is
39. applications can request frame skipping or duplicating on the driver side This is especially useful when using the read or write which are not augmented by timestamps or sequence counters and to avoid unneccessary data copying Further these ioctls can be used to determine the number of buffers used internally by a driver in read write mode For implications see the section discussing the read function To get and set the streaming parameters applications call the vVIDIOC G PARM and VIDIOC S PARM ioctl respectively They take a pointer to a struct v412_streamparm which contains a union holding separate parameters for input and output devices Table 1 struct v4l2 streamparm enum v4lI2 buf typetype union parm struct v412_captureparmt ure The buffer stream type same as struct v412_format type set by the application Parameters for capture devices used when type is V4L2_BUF_TYPE_VIDEO_CAPTURE 116 struct v412_outputpaom t put u8 Table 2 struct v4l2 captureparm u32 capability u32 capturemode struct v412 fract timeperframe u32 extendedmode u32 readbuffers u32 reserved 4 Table 3 struct v412_outputparm raw data 200 ioctl VIDIOC_G_PARM VIDIOC S8 PARM Parameters for output devices used when type is VAL2 BUF TYPE VIDEO OUTPUT A place holder for future extensions and custom driver defined buffer types VAL2 BUF TYPE PRIVATE and higher
40. buffers or to free the allocated memory provided none of the buffers are still mapped Before applications can access the buffers they must map them into their address space with the mmap function The location of the buffers in device memory can be determined with the VIDIOC_QUERYBUF ioctl The m offset and length returned in a struct vAI2 buffer are passed as sixth and second parameter to the mmap function The offset and length values must not be modified Remember the buffers are allocated in physical memory as opposed to virtual memory which can be swapped out to disk Applications should free the buffers as soon as possible with the munmap function Example 3 1 Mapping buffers struct v412 requestbuffers reqbuf SUrudot void xstart Size t length xbuffers unsigned int i memset amp reqbuf 0 sizeof reqbuf reqbuf type V4L2_BUF_TYPE_VIDEO_CAPTURE reqbuf memory V4L2_MEMORY_MMAP reqbuf count 20 E if 1 ioctl fd VIDIOC_REQBUFS amp reqbuf if errno EINVAL printf Video capturing or mmap streaming is not supported n else perror VIDIOC_REQBUFS exit EXIT_FAILURE We want at least five buffers x if regbuf count lt 5 You may need to fr the buffers here x printf Not enough buffer memory n exit EXIT FAILURE 38 Chapter 3 Input Output buffers calloc reqbuf count
41. devices are accessed through character device special files named dev video and dev videoO to dev video63 with major number 81 and minor numbers 0 to 63 dev video is typically a symbolic link to the preferred video capture device 4 1 1 Querying Capabilities Devices supporting the video capture interface set the VAL2 CAP VIDEO CAPTURE flag in the capabilities field of struct v412 capability returned by the VIDIOC_QUERYCAP As secondary device functions they may also support the video overlay V4L2 CAP VIDEO OVERLAY and the raw VBI capture V4AL2 CAP VBI CAPTURE interface At least one of the read write or streaming I O methods must be supported Tuners and audio inputs are optional 4 1 2 Supplemental Functions Video capture devices shall support audio input tuner controls cropping and scaling and streaming parameter ioctls as needed The video input and video standard ioctls must be supported by all video capture devices 4 1 3 Image Format Negotiation The result of a capture operation is determined by cropping and image format parameters The former select an area of the video picture to capture the latter how images are stored in memory i e in RGB or YUV format the number of bits per pixel or width and height Together they also define how images are scaled in the process As usual these parameters are not reset at open time to permit Unix tool chains programming a device and then reading from i
42. driver see Section 2 2 gt u32 priv Reserved for custom driver defined additional information about formats When not used drivers and applications must set this field to zero 2 1 Standard Image Formats In order to exchange images between drivers and applications it is necessary to have standard image data formats which both sides will interpret the same way V4L2 includes several such formats and this section is intended to be an unambiguous specification of the standard image data formats in V4L2 VAL2 drivers are not limited to these formats however Driver specific formats are possible In that case the application may depend on a codec to convert images to one of the standard formats when needed But the data can still be stored and retrieved in the proprietary format For example a device may support a proprietary compressed format Applications can still capture and save the data in the 21 Chapter 2 Image Formats compressed format saving much disk space and later use a codec to convert the images to the X Windows screen format when the video is to be displayed Even so ultimately some standard formats are needed so the V4L2 specification would not be complete without well defined standard formats The V4L2 standard formats are mainly uncompressed formats The pixels are always arranged in memory from left to right and from top to bottom The first byte of data in the image buffer is always for the leftmost pixel
43. drivers implementing the sliced VBI interface must support this ioctl The results may differ from those of the VIDIOC_S_FMT ioctl when the number of VBI lines the hardware can capture or output per frame or the number of services it can identify on a given line are limited For example on PAL line 16 the hardware may be able to look for a VPS or Teletext signal but not both at the same time To determine the currently selected services applications set the type field of struct v412 format to V4L2 BUF TYPE SLICED VBI CAPTURE OrV4L2 BUF TYPE SLICED VBI OUTPUT and the VIDIOC G FMT ioctl fills the fmt sliced member a struct v412 sliced vbi format Applications can request different parameters by initializing or modifying the fmt sliced member and calling the VIDIOC_S_FMT ioctl with a pointer to the v412 format structure The sliced VBI API is more complicated than the raw VBI API because the hardware must be told which VBI service to expect on each scan line Not all services may be supported by the hardware on all lines this is especially true for VBI output where Teletext is often unsupported and other services can only be inserted in one specific line In many cases however it is sufficient to just set the service set field to the required services and let the driver fill the service lines array according to hardware capabilities Only if more precise control is needed should the programmer set the
44. eR bte lee terit evel eee Hec y eterne iden 44 3 3 Butler Flags 5 us ehem eed ee ES 44 324 enum VAI2 MEMO e uenis tete ree e pee tede deo i ede eee dote i le ces eei a 45 3 5 struct yAD2 timecode 2 eene nREIn E Om re MM aee 45 3 6 Timec de Types udesdecatiieue p ee tiene eue P ene etes bin Pee ESS 46 3 7 Timecode Flags i neben eI p S Ei SS 46 3 5 enum v4lI2 fela 3c ete eerte eee ye tee ee Ueber e eee eene cete 47 4 str ct V4D2 wIndOW ed Rete nO ss nU RR 54 4 2 struct VAD clipes ted eet estet ete BTS ect 54 423 struct V4I2 TeC cincti e EENEIEE cous do suse NECS ER EE WEGE ces davuseve EEE FEES VES USER EE 55 4 4 struct v4I2 vbi format sssssssseeeeeeeenenen enne een ener nnns eene n sen ee etin rete nasa sse sensere eset nnn 58 4 5 Raw VBI Format Flags cor oi bes tt e e Ia Eee ee este 59 4 6 struct v4I2 sliced vbi format ssseseeeeeeeeene ene n en nne en ennt nennt nn nnne reser serene nnn 65 Aa SIGE VBLServIe8S etre erede aie ere RD eee bre deest ete debe ege Sedit 66 4 8 struct V412_ sliced _Vbi_ ata ciicccececsssssssssececccceccccescesevessssseusescscscsesescescesesecsessauauscseseseseeseeeenens 66 1 struct v4l2 Cropcap oe o eer ree cie I rete pie dee on ule ice iere 75 Fs Oe he see osse 9 NI ao OX S X ES RS o vast pas des dba e pa struct VAI s Teeb o e teo ette tie eee eed IE GM i 76 struct V4I2 zfmtdese e a E i neve d e reet 79 Image Format Description Flags
45. entitled History in the Document create one stating the title year authors and publisher of the Document as given on its Title Page then add an item describing the Modified Version as stated in the previous sentence e J Preserve the network location if any given in the Document for public access to a Transparent copy of the Document and likewise the network locations given in the Document for previous versions it was based on These may be placed in the History section You may omit a network location for a work that was published at least four years before the Document itself or if the original publisher of the version it refers to gives permission e K In any section entitled Acknowledgements or Dedications preserve the section s title and preserve in the section all the substance and tone of each of the contributor acknowledgements and or dedications given therein 214 Appendix C GNU Free Documentation License L Preserve all the Invariant Sections of the Document unaltered in their text and in their titles Section numbers or the equivalent are not considered part of the section titles M Delete any section entitled Endorsements Such a section may not be included in the Modified Version N Do not retitle any existing section as Endorsements or to conflict in title with any Invariant Section If the Modified Version includes new front matter sections or appendices that qualify as Sec
46. field ooc tbd The timecode field is valid Drivers set or clear this flag when the VIDIOC_DQBUF ioctl is called The input field is valid Applications set or clear this flag before calling the VIDIOC_QBUF ioctl The buffer is used for memory mapping I O The buffer is used for user pointer I O to do The v412_ timecode structure is designed to hold a SMPTE12M gt or similar timecode struct timeval timestamps are stored in struct v412_buffer field timestamp Table 3 5 struct v4l2 timecode u32 u32 u8 u8 type flags frames seconds Frame rate the timecodes are based on see Table 3 6 Timecode flags see Table 3 7 Frame count 0 23 24 29 49 59 depending on the type of timecode Seconds count 0 59 This is a binary not BCD number 45 Chapter 3 Input Output u8 minutes Minutes count 0 59 This is a binary not BCD number u8 hours Hours count 0 29 This is a binary not BCD number u8 userbits 4 The user group bits from the timecode Table 3 6 Timecode Types V4L2 TC TYPE 24FPS 1 24 frames per second i e film V4L2 TC TYPE 25FPS 2 25 frames per second i e PAL or SECAM video V4L2 TC TYPE 30FPS 3 30 frames per second i e NTSC video VA4L2 TC TYPE 50FPS 4 VAL2 TC TYPE 60FPS 5 Table 3 7 Timecode Flags V4L2 TC FLAG DROPFRAME 0x0001 Indicates drop frame semantics for counting frames in 29 97 fps material
47. gt include lt string h gt include lt assert h gt include lt getopt h gt getopt long include fcntl h low level i o x include lt unistd h gt include lt errno h gt include lt sys stat h gt include lt sys types h gt include lt sys time h gt include lt sys mman h gt include lt sys ioctl h gt include lt asm types h gt for videodev2 h x include lt linux videodev2 h gt define CLEAR x memset amp x 0 sizeof x typedef enum IO_METHOD_READ IO_METHOD_MMAP IO_METHOD_USERPTR io method T struct buffer void start size t length un static char dev name NULL static io method io IO METHOD MMAP static int fd 1 struct buffer x buffers NULL static unsigned int n buffers 0 static void errno_exit const char x S fprintf stderr s error d s n S errno strerror errno 200 Appendix B Video Capture Example exit EXIT FAILURE static int ioctl int fd int request void x arg ae es do r ioctl fd request arg while 1 r amp amp EINTR errno return r static void process image const void x p fputc stdout fflush stdout static int read frame void struct v412 buffer buf unsigned int i switch io case IO METHOD READ if 1 read fd buffers 0 start buffers 0 length switch errno case EAGAIN
48. is supported AVL mode is on On success 0 is returned on error 1 and the errno variable is set appropriately EINVAL No audio inputs combine with the current video input or the number of the selected audio input is out of bounds or it does not combine or there are no audio inputs at all and the ioctl is not supported EBUSY I O is in progress the input cannot be switched 91 ioctl VIDIOC G AUDOUT VIDIOC S AUDOUT Name VIDIOC G AUDOUT VIDIOC S AUDOUT Query or select the current audio output Synopsis int ioctl int fd int request struct v412 audioout xargp int ioctl int fd int request const struct v412 audioout argp Arguments fd File descriptor returned by open request VIDIOC G AUDOUT VIDIOC 5 AUDOUT argp Description To query the current audio output applications zero out the reserved array of a struct v412_audioout and call the VIDIOC_G_AUDOUT ioctl with a pointer to this structure Drivers fill the rest of the structure or return an EINVAL error code when the device has no audio inputs or none which combine with the current video output Audio outputs have no writable properties Nevertheless to select the current audio output applications can initialize the index field and reserved array which in the future may contain writable properties of a v412_audioout structure and call the vIDIOC_S_AUDOUT ioctl Drivers switch to the requested output or return the EINVAL error cod
49. may support another set of standards This set is reported by the std field of struct v412_input and struct v412 output returned by the VIDIOC_ENUMINPUT and VIDIOC_ENUMOUTPUT ioctl respectively VAL2 defines one bit for each analog video standard currently in use worldwide and sets aside bits for driver defined standards e g hybrid standards to watch NTSC video tapes on PAL TVs and vice versa Applications can use the predefined bits to select a particular standard although presenting the user a menu of supported standards is preferred To enumerate and query the attributes of the supported standards applications use the VIDIOC_ENUMSTD ioctl Many of the defined standards are actually just variations of a few major standards The hardware may in fact not distinguish between them or do so internal and switch automatically Therefore enumerated standards also contain sets of one or more standard bits Assume a hypothetic tuner capable of demodulating B PAL G PAL and I PAL signals The first enumerated standard is a set of B and G PAL switched automatically depending on the selected radio frequency in UHF or VHF band Enumeration gives a PAL B G or PAL I choice Similar a Composite input may collapse standards enumerating PAL B G H T NTSC M and SECAM D K To query and select the standard used by the current video input or output applications call the VIDIOC G STD and VIDIOC S STD ioctl respectively The received standa
50. name 32 u32 capability u32 rangelow u32 rangehigh u32 txsubchans u32 reserved 4 Table 2 Modulator Audio Transmission Flags V4L2 TUNER SUB MONO 0x0001 V4L2 TUNER SUB STEREO 0x0002 Identifies the modulator set by the application Name of the modulator a NUL terminated ASCII string This information is intended for the user Modulator capability flags No flags are defined for this field the tuner flags in struct v412 tuner are used accordingly The audio flags indicate the ability to encode audio subprograms They will not change for example with the current video standard The lowest tunable frequency in units of 62 5 KHz or if the capability flag V4L2_TUNER_CAP_LOW is set in units of 62 5 Hz The highest tunable frequency in units of 62 5 KHz or if the capability flag V4L2_TUNER_CAP_LOW is set in units of 62 5 Hz With this field applications can determine how audio sub carriers shall be modulated It contains a set of flags as defined in Table 2 Note the tuner rxsubchans flags are reused but the semantics are different Video output devices are assumed to have an analog or PCM audio input with 1 3 channels The txsubchans flags select one or more channels for modulation together with some audio subprogram indicator for example a stereo pilot tone Reserved for future extensions Drivers and applications must set the array to zero Modulate channel 1 as mono
51. of buffers applications can enqueue in advance or dequeue and process They can also enqueue in a different order than buffers have been dequeued and the driver can fill enqueued empty buffers in any order The index number of a buffer struct v412_buffer index plays no role here it only identifies the buffer Initially all mapped buffers are in dequeued state inaccessible by the driver For capturing applications it is customary to first enqueue all mapped buffers then to start capturing and enter the read loop Here the application waits until a filled buffer can be dequeued and re enqueues the buffer when the data is no longer needed Output applications fill and enqueue buffers when enough buffers are stacked up the output is started with VIDIOC_STREAMON In the write loop when the application runs out of free buffers it must wait until an empty buffer can be dequeued and reused 39 Chapter 3 Input Output To enqueue and dequeue a buffer applications use the VIDIOC_QBUF and VIDIOC_DQBUF ioctl The status of a buffer being mapped enqueued full or empty can be determined at any time using the VIDIOC_QUERYBUF ioctl Two methods exist to suspend execution of the application until one or more buffers can be dequeued By default viproc poBur blocks when no buffer is in the outgoing queue When the o NONBLOCK flag was given to the open function VIDIOC DOBUF returns immediately with an EAGAIN error code when no buffer is available
52. of the topmost row Following that is the pixel immediately to its right and so on until the end of the top row of pixels Following the rightmost pixel of the row there may be zero or more bytes of padding to guarantee that each row of pixel data has a certain alignment Following the pad bytes if any is data for the leftmost pixel of the second row from the top and so on The last row has just as many pad bytes after it as the other rows In V4L2 each format has an identifier which looks like PIX FMT XXX defined in the videodev h header file These identifiers represent four character codes which are also listed below however they are not the same as those used in the Windows world 2 2 Colorspaces intro Gamma Correction to do E KR E 2 f G E f B Construction of luminance and color difference signals to do E Coeff E p Coeff E Coeff E E E E Coeff E Coeff E Coeff E E E E Coeff FE Coeff E Coeff E Re normalized color difference signals The color difference signals are scaled back to unity range 0 5 0 5 K 0 5 1 Coeff K 0 5 1 Coeff P K E E 2 0 5 Coeff Coeff E p 0 5 Coeff Coeff E 0 5 E P K E Ey 20 5 E 0 5 Coeff Coeff E 0 5 Coeff Coeff E Quantization to do Y Lum Levels 1 E Lum Offset C Chrom Levels 1 Pa Chrom Offset 22 C
53. older the temporal order When the driver provides or accepts images field by field rather than interleaved it is also important applications understand how the fields combine to frames We distinguish between top and bottom fields the spatial order The first line of the top field is the first line of an interlaced frame the first line of the bottom field is the second line of that frame 46 Chapter 3 Input Output However because fields were captured one after the other arguing whether a frame commences with the top or bottom field is pointless Any two successive top and bottom or bottom and top fields yield a valid frame Only when the source was progressive to begin with e g when transferring film to video two fields may come from the same frame creating a natural order Counter to intuition the top field is not necessarily the older field Whether the older field contains the top or bottom lines is a convention determined by the video standard Hence the distinction between temporal and spatial order of fields The diagrams below should make this clearer All video capture and output devices must report the current field order Some drivers may permit the selection of a different order to this end applications initialize the field field of struct v412_pix_format before calling the vIDIOC_S_FMT ioctl If this is not desired it should have the value VAL2 FII Table 3 8 enum v4D2 field VAL2 FIELD ANY VAL2 FI
54. outputs are physical connectors of a device These can be for example RF connectors antenna cable CVBS a k a Composite Video S Video or RGB connectors Only video and VBI capture devices have inputs output devices have outputs at least one each Radio devices have no video inputs or outputs To learn about the number and attributes of the available inputs and outputs applications can enumerate them with the VIDIOC_ENUMINPUT and VIDIOC ENUMOUTPUT ioctl respectively The struct v4I2 input returned by the VIDIOC_ENUMINPUT ioctl also contains signal status information applicable when the current video input is queried The VIDIOC_G_INPUT and VIDIOC G OUTPUT ioctl return the index of the current video input or output To select a different input or output applications call the VIDIOC_S_INPUT and VIDIOC S OUTPUT ioctl Drivers must implement all the input ioctls when the device has one or more inputs all the output ioctls when the device has one or more outputs Example 1 1 Information about the current video input struct v412 input input int index if 1 ioctl fd VIDIOC G INPUT amp index perror VIDIOC G INPUT exit EXIT FAILURE memset amp input 0 sizeof input input index index if 1 ioctl fd VIDIOC ENUMINPUT amp input perror VIDIOC ENUMINPUT exit EXIT_FAILURE printf Current input s n input name Chapter 1 Common API Elements Example 1
55. struct v412 input input v412_std_id std_id memset amp input 0 sizeof input if 1 ioctl fd VIDIOC_G_INPUT amp input index perror VIDIOC G INPUT exit EXIT FAILURE if 1 ioctl fd VIDIOC ENUMINPUT amp input perror VIDIOC ENUM INPUT exit EXIT FAILURE T if 0 input std amp V4L2_STD_PAL_BG fprintf stderr Oops B G PAL is not supported n exit EXIT_FAILURE Note this is also supposed to work when only B or G PAL is supported x std id VA4L2 STD PAL BG if 1 ioctl fd VIDIOC S STD amp std id perror VIDIOC S STD exit EXIT FAILURE Chapter 1 Common API Elements 1 8 Controls Devices typically have a number of user settable controls such as brightness saturation and so on which would be presented to the user on a graphical user interface But different devices will have different controls available and furthermore the range of possible values and the default value will vary from device to device The control ioctls provide the information and a mechanism to create a nice user interface for these controls that will work correctly with any device All controls are accessed using an ID value VAL2 defines several IDs for specific purposes Drivers can also implement their own custom controls using V4AL2 CID PRIVATE BASE and higher values The pre defined control IDs have the prefix V4L2 CI
56. success 0 is returned on error 1 and the errno variable is set appropriately EBUSY count type memory reserved 32 ioctl VIDIOC REQBUFS The number of buffers requested or granted This field is only used when memory is set to V4L2 MEMORY MMAP Type of the stream or buffers this is the same as the struct v412 format t ype field See Table 3 2 for valid values Applications set this field to vVAL2 Mi or V4L2 MEMORY USERPTR EMORY MMAP A place holder for future extensions and custom driver defined buffer types VAL2 BUF TYPE PRIVATI E and higher The driver supports multiple opens and I O is already in progress or reallocation of buffers was attempted although one or more are still mapped EINVAL The buffer type t ype field or the requested I O method memory is not supported 144 Notes 1 For example video output requires at least two buffers one displayed and one filled by the application ioctl VIDIOC STREAMON VIDIOC STREAMOFF Name VIDIOC STREAMON VIDIOC STREAMOFF Start or stop streaming I O Synopsis int ioctl int fd int request const int xargp Arguments fd File descriptor returned by open request VIDIOC_STREAMON VIDIOC_STREAMOFF argp Description The VIDIOC_STREAMON and VIDIOC_STREAMOFF ioctl start and stop the capture or output process during streaming memory mapping or user pointer I O Specifically the cap
57. the EAGAIN error code when no data is available or no buffer is in the driver outgoing queue otherwise these functions block until data becomes available All V4L2 drivers exchanging data with applications must support the O NONBLOCK flag Other flags have no effect Description To open a V4L2 device applications call open with the desired device name This function has no side effects all data format parameters current input or output control values or other properties remain unchanged At the first open call after loading the driver they will be reset to default values drivers are never in an undefined state Return Value On success open returns the new file descriptor On error 1 is returned and the errno variable is set appropriately Possible error codes are EACCES The caller has no permission to access the device EBUSY The driver does not support multiple opens and the device is already in use 150 V4L2 open ENXIO No device corresponding to this device special file exists ENOMEM Insufficient kernel memory was available EMFILE The process already has the maximum number of files open ENFILE The limit on the total number of files open on the system has been reached 151 V4L2 poll Name v412 poll Wait for some event on a file descriptor Synopsis finclude lt sys poll h gt int poll struct pollfd xufds unsigned int nfds int timeout Description All drivers impl
58. the VIDIOC_QUERYCTRL and VIDIOC_QUERYMENU ioctls get and set a control value with the VIDIOC_G_CTRL and VIDIOC_S_CTRL ioctls Drivers must implement VIDIOC_QUERYCTRL VIDIOC G CTRL and VIDIOC_S_CTRL when the device has one or more controls VIDIOC_QUERYMENU when it has one or more menu type controls Example 1 8 Enumerating all controls struct v412 queryctrl queryctrl struct v412 querymenu querymenu static void enumerate menu printf memset void Menu items n amp querymenu querym 0 sizeof nu id queryctrl id querymenu 1l Chapter 1 Common API Elements for querymenu index queryctrl minimum querymenu index queryctrl maximum querymenu index if 0 ioctl fd VIDIOC_QUERYMENU amp querymenu printf s n querymenu name else perror VIDIOC_QUERYMENU exit EXIT_FAILURE memset amp queryctrl 0 sizeof queryctrl for queryctrl id V4L2_CID_BASE queryctrl id lt V4L2_CID_LASTP1 queryctrl id if 0 ioctl fd VIDIOC QUERYCTRL amp queryctrl if queryctrl flags amp V4L2 CTRL FLAG DISABLED continue printf Control s n queryctrl name if queryctrl type V4L2 CTRL TYPE MENU enumerate menu else if errno EINVAL continue perror VIDIOC QUERYCTRL exit EXIT FAILURE for quer
59. type V4L2 BUF TYPE PRIVATE and higher On success 0 is returned on error 1 and the errno variable is set appropriately 103 ioctl VIDIOC G FMT VIDIOC S FMT VIDIOC TRY FMT EBUSY The data format cannot be changed at this time for example because I O is already in progress EINVAL The struct v412 format type field is invalid the requested buffer type not supported or VIDIOC TRY FMT was called and is not supported with this buffer type 104 ioctl VIDIOC G FREQUENCY VIDIOC S FREQUENCY Name VIDIOC G FREQUENCY VIDIOC S FREQUENCY Get or set tuner or modulator radio frequency Synopsis int ioctl int fd int request struct v412 frequency xargp int ioctl int fd int request const struct v412 frequency argp Arguments fd File descriptor returned by open request VIDIOC G FREQUENCY VIDIOC 5 FREQUENCY argp Description To get the current tuner or modulator radio frequency applications set the tuner field of a struct v4I2 frequency to the respective tuner or modulator number only input devices have tuners only output devices have modulators zero out the reserved array and call the VIDIOC G FREQUENCY ioctl with a pointer to this structure The driver stores the current frequency in the requency field To change the current tuner or modulator radio frequency applications initialize the tuner and frequency fields and the reserved array o
60. type V4L2_BUF_TYPE_VIDEO_CAPTURE if 1 xioctl fd VIDIOC STREAMON amp type errno exit VIDIOC STREAMON break case IO METHOD USERPTR for i 0 i n buffers i struct v412 buffer buf CLEAR buf buf type VA4L2 BUF TYPE VIDEO CAPTURE buf memory VAL2 MEMORY USERPTR buf m userptr unsigned long buffers i start buf length TE SI errno_exit xioctl buffers i length fd VIDIOC_QBUF VIDIOC_QBUF amp buf 204 type acp s break static void uninit device Appendix B Video Capture Example V4L2_BUE TYP EO CAPTURE VID xioctl errno exit fd VIDIOC ST EAMON AMON amp type Aw VIDIOC_STR void unsigned int i switch io case IO METHOD READ free buffers 0 start break case IO METHOD MMAP for i break 0 X Ee errno exit case IO METHOD USERPTR for i 0 free break free buffers static void init_read buffers calloc 1 sizeof if buffers fprintf stderr exit EXIT_FAILURE unsigned int i n buffers i n buffers buffers i start i buffers i start munmap munmap buffers i length i buffer_size xbuffers Out of memory n buffers 0 length buffer siz buffers 0 start if buffers 0 fprint exit static v
61. vbi format u32 sampling rate in 1 Hz x u32 offset u32 samples_per_line u32 sample format VAL2 PIX FMT s32 start 2 u32 count 2 u32 flags VAL2 VBI u32 reserved 2 must be zero VBI flags define V4L2_VBI_UNSYNC 1 0 define V4L2 VBI INTERLACED 1 1 if 1 KEEP x Sliced VBI This implements is a proposal V4L2 API to allow SLICED VBI required for some hardware encoders notice in the definitive implementation struct v412_sliced_vbi_format FERE Service set service lines 0O service lines 1 It should change without Specifies lines 0 23 1 23 used of the first field specifies lines 0 23 1 23 used of the second field equals frame lines 313 336 for 625 line video standards 263 286 for 525 line standards 195 _ ule 2032 u32 define V4 2 SLICE service lines 2 24 io size reserved 2 D_TEL ETEXT_B define V4 i2 SLIC s define V4 I define V4 I define V4 T define V4 I ul6 service lines 0O service lines 1 ul6 1032 D VPS 2 SLICED CAPTION 525 2 SLICED WSS 625 i2 SLICED VBI 525 2 SLICED VBI 625 struct v412 sliced vbi cap Service set service lines 2 24 reserved 4 must be 0 x struct v412 sliced v
62. void init userp struct v412 requestbuffers req CLEAR req unsigned int Appendix B Video Capture Example buffer size req count 4 req type V4L2_BUF_TYPE_VIDEO_CAPTURE req memory V4L2_MEMORY_USERPTR if 1 xioctl fd VIDIOC REQBUFS amp req if EINVAL errno fprintf stderr Ss does not support user pointer i o n dev_name exit EXIT FAILURE else errno exit VIDIOC_REQBUFS buffers calloc 4 sizeof bu if buffers fprintf stderr Out of exit EXIT FAILURE for n buffers 0 n buffers ffers memoryNn 4 n buffers buffers n buffers length buffer size buffers n buffers start if buffers n buffers fprintf stderr malloc buffer size start Out of memory Nn exit EXIT FAILURE static void init device void struct v412 capability cap struct v412 cropcap cropcap struct v412 crop crop struct v412 format fmt unsigned int min if 1 xioctl fd VIDIOC_QUE if EINVAL errno fprintf stderr RYCAP amp cap Ss is no V4L2 device n dev_name exit EXIT FAILURE else errno_exit VID IOC QUERYCAP 207 Appendix B Video Capture Example if cap capabilities amp V4L2 CAP VIDEO CAPTURE fprintf stderr s is no video c
63. 000 The device supports the streaming I O method Return Value On success 0 is returned on error 1 and the errno variable is set appropriately EINVAL The kernel device is not compatible with this specification 137 ioctl VIDIOC QUERYCTRL VIDIOC QUERYMENU Name VIDIOC QUERYCTRL VIDIOC QUERYMENU Enumerate controls and menu control items Synopsis int ioctl int fd int request struct v412 queryctrl xargp int ioctl int fd int request struct v412 querymenu xargp Arguments fd File descriptor returned by open request VIDIOC_QUERYCTRL VIDIOC_QUERYMENU argp Description To query the attributes of a control applications set the id field of a struct v412_queryctrl and call the VIDIOC_QUERYCTRL ioctl with a pointer to this structure The driver fills the rest of the structure or returns an EINVAL error code when the id is invalid It is possible to enumerate controls by calling VIDIOC_QUERYCTRL with successive id values starting from V4L2_CID_BASE up to and exclusive V4L2_CID_BASE_LASTP1 or starting from V4L2_CID_PRIVATE_BASE until the driver returns EINVAL When the V4L2_CTRL_FLAG_DISABLED flag is set in the flags field this control is permanently disabled and should be ignored by the application Additional information is required for menu controls the name of menu items To query them applications set the id and index fields of struct v412_querymenu an
64. 0008 Image is a keyframe I frame x define V4L2 BUF FLAG PFRAME 0x0010 x Image is a P frame define VA4L2 BUF FLAG BFRAME 0x0020 Image is a B frame define V4L2 BUF FLAG TIMECODE 0x0100 x timecode field is valid define VA4L2 BUF FLAG INPUT 0x0200 input field is valid x x OVERLAY PREVIEW x struct v412 framebuffer u32 capability u32 flags x FIXME in theory we should pass something like PCI device memory offset instead of void region 4 some physical address base struct v412 pix format fmt Flags for the capability field Read only define V4L2 FBUF CAP EXTERNOVERLAY 0x0001 define V4L2 FBUF CAP CHROMAKEY 0x0002 define V4L2 FBUF CAP LIST CLIPPING 0x0004 188 Appendix A Video For Linux Two Header File define V4L2 FBUF CAP BITMAP CLIPPING 0x0008 Flags for the flags field x define V4L2 FBUF FLAG PRIMARY 0x0001 define V4L2 FBUF FLAG OVERLAY 0x0002 define V4L2 FBUF FLAG CHROMAKEY 0x0004 struct v412 clip struct v412 rect s struct v412 clip xnext struct v412_window struct v412 rect WwW enum v412 field field lt 1132 chromakey struct v412 clip user clips u32 clipcount void user xbitmap CAP TUER PARAM TE RS struct v412 captureparm u32 capability Supported modes u32 capturemode Current mode x str
65. 01 Attached device is off 191 field status field status define VA4L2 I define V4L2 IN S field status define VA4L2 IN ST define VA4L2 I define V4L2 IN ST VTR NC a D Er struct v412 output O Q U T P U TS Appendix A Video For Linux Two Header File define VA4L2 IN ST NO SIGNAL 0x00000002 define V4L2 IN ST NO COLOR 0x00000004 analog x define V4L2 IN ST NO H LOCK 0x00000100 No horizontal sync lock x define V4L2 IN ST COLOR KILL 0x00000200 x Color killer is active digital x ST NO SYNC 0x00010000 No synchronization lock x ST NO EQU 0x00020000 x No equalizer lock define V4L2 IN ST NO CARRIER 0x00040000 x Carrier recovery failed VCR and set top box MACROVISION 0x01000000 x Macrovision detected ST NO ACCESS 0x02000000 x Conditional access denied 0x04000000 VTR time constant x u32 index Which output u8 name 32 Label u32 type Type of output x u32 audioset Associated audios bitfield x u32 modulator Associated modulator x v412 std id std c M32 reserved 4 Values for the type field define V4L2_OUTPUT_TYPE_MODULATOR define V4L2_OUTPUT_TYPE_ANALOG define V4L2_OUTPUT_TYPE_ANALOGVGAOVERLAY 3 CONTROLS struct v412 control he Use
66. 1 and the errno variable is set appropriately EINVAL The struct v412_cropcap type is invalid or the ioctl is not supported This is not permitted for video capture output and overlay devices which must support VIDIOC_CROPCAP 76 ioctl VIDIOC ENUMAUDIO Name VIDIOC ENUMAUDIO Enumerate audio inputs Synopsis int ioctl int fd int request struct v412 audio xargp Arguments fd File descriptor returned by open request VIDIOC ENUMAUDIO argp Description To query the attributes of an audio input applications initialize the index field and zero out the reserved array of a struct v412 audio and call the VIDIOC_ENUMAUDIO ioctl with a pointer to this structure Drivers fill the rest of the structure or return an EINVAL error code when the index is out of bounds To enumerate all audio inputs applications shall begin at index zero incrementing by one until the driver returns EINVAL See ioctl VIDIOC G AUDIO VIDIOC S AUDIO 2 for a description of struct v412 audio Return Value On success 0 is returned on error 1 and the errno variable is set appropriately EINVAL The number of the audio input is out of bounds or there are no audio inputs at all and this ioctl is not supported 77 ioctl VIDIOC ENUMAUDOUT Name VIDIOC ENUMAUDOUT Enumerate audio outputs Synopsis int ioctl int fd int request struct v412 audioout xargp Arguments fd File descriptor returned by open
67. 2 422 Supplemental Functions npo ert drei a eerte E 52 4 2 3 Setup e cU agere EUROS GUB uU BUSES 52 4 2 4 Overlay Window oeste beso eite epi rei ep te 53 4 2 5 Enabling Overlay iio i eset e e WEA eene 55 4 3 Video Output Interface nete ia nite eite pe HARE t e pp E 55 4 3 1 Querying Capabilities eue eidem erige RES 55 4 3 2 Supplemental FUNCIONS s isisi isiin e eot ta etie 55 4 3 3 Image Format Negotiation eren en enemies 56 4 3 4 Writing Images ieiuno ee dier eerte 56 4 A Codec Interface oz gone SO RO qu Re RO tee lil RI RS 56 4 5 Effect Devices Interface ient tea temp utt peior erp iS 56 4 6 Raw VBI Data Interface oett o te tese t nba eee reducere ei 57 4 6 1 Querymg Capabilities edere eter teer ea beret 57 4 6 2 Supplemental Functions eeeesssseeeeeeeeeen trennen eren en nennen nnne 57 4 6 3 Raw VBI Format Negotiation eren nennen retener 57 4 6 4 Reading and writing VBI images eeeseeseeeeeenen enne emere 64 4 7 Sliced VBI Data Interface vx sc ertet etre tae be br Det bei 64 4 71 Querymg Capabilities oet eu r mU DU vacant Ae 64 4 7 2 Supplemental Functions eoe tei e tret rente 65 4 7 3 Sliced VBI Format Negotiation eseessseeseeeeeeeee eene nennen nene 65 4 7 4 Reading and writing sliced VBI data esse 66 4 8 Teletext Interface edet uto nebenbei eut 67 4 9 Radio Interface eiie eto eee Dua
68. 2 PIX FMT RGB555X and V4L2 PIX FMT RGB565x formats are uncommon Video and display hardware typically supports 26 variants with reversed order of color components i e blue towards the least red towards the most significant bit Although presumably the original authors had the common formats in mind the definitions were always very clear and cannot be simply regarded as erroneous If vaL2 PIX FMT RGB332 has been chosen in accordance with the 15 and 16 bit formats this format might as well be interpreted differently as rrrgggbb rather than bbgggrrr Finally some drivers most prominently the BTTV driver might interpret vaL2 PIX FMT RGB32 as the big endian variant of v4L2_P1X_FMT_BGR32 consisting of bytes RGB in memory V4L2 never defined such a format lack of a x suffix to the symbol suggests it was intended this way and a new symbol and four character code should have been used instead Until these issues are solved application writers are advised that drivers might interpret these formats either way 2 4 YUV Formats YUV is the format native to TV broadcast and composite video signals It separates the brightness information Y from the color information U and V or Cb and Cr The color information consists of red and blue color difference signals this way the green component can be reconstructed by subtracting from the brightness component See Section 2 2 for conversion examples YUV was chosen because early telev
69. 2 Switching to the first video input int index index 0 if 1 ioctl fd VIDIOC S INPUT amp index perror VIDIOC S INPUT exit EXIT_FAILURE 1 5 Audio Inputs and Outputs Audio inputs and outputs are physical connectors of a device Video capture devices have inputs output devices have outputs zero or more each Radio devices have no audio inputs or outputs They have exactly one tuner which in fact is an audio source but this API associates tuners with video inputs or outputs only and radio devices have none of these A connector on a TV card to loop back the received audio signal to a sound card is not considered an audio output Audio and video inputs and outputs are associated Selecting a video source also selects an audio source This is most evident when the video and audio source is a tuner Further audio connectors can combine with more than one video input or output Assumed two composite video inputs and two audio inputs exist there may be up to four valid combinations The relation of video and audio connectors is defined in the audioset field of the respective struct v412_input or struct v412_output where each bit represents the index number starting at zero of one audio input or output To learn about the number and attributes of the available inputs and outputs applications can enumerate them with the VIDIOC_ENUMAUDIO and VIDIOC_ENUMAUDOUT ioctl respectively The struct v412_audio returned by
70. 28 proba bly 24 Chapter 2 Image Formats Identifier Value DescriptionChromaticities WhiteGamma Lumi Point Correc inance Red Green Blue Y Cb Cr tion Ev VAL2 CQLOREPAGM N TIG Gw SERT 0 21 x 0 14 accord y 20 33 y 0 71 y 0 08 x 20 310 0 299 E 219 E v 224 Par 128 ing to y 20 316 H 0 587 B c ITUA70 Mumi H0 114 B s ITU601 gt nant C V4L2 CGLOR PAQ 25HineSx 1084 BG 0 29 x 0 15 PAL and y 0 33 y 0 60 y 0 06 x 20 313 0 299 E 219 E v 224 Par 128 SECAM y 0 329 H 0 587 B c systems Humi 0 114 B s accord nant Des ing to ITU470 gt ITU601 gt V4L2 CGQLORBPAGBPEGEG Y CbCr 0 299 E 256 E v 206 Ps 128 see H 0 587 B c JFIF gt 0 114H s ITU601 gt V4L2 CQLORSPAQ SRGB F X 0 640x 0 300x 0 150x 0 3124 5 I for I lt 0 018 y 0 330y 0 600 0 060y 0 32910 099 Ios Illumi 0 099 for 0 018 lt I Inant Des Notes a The coordinates of the color primaries are given in the CIE system 1931 b The ubiquitous Bt878 video 2 3 RGB Formats These formats are designed to match the pixel formats of typical PC graphics frame buffers They occupy 8 16 24 or 32 bits per pixel These are all packed pixel formats meaning all the data for a pixel lie next to each other in memory When one of these formats is used drivers shall report the colorspace V4L2_COLORSPACE_SRGB Table 2
71. 3 1 4 Video Inputs and Outputs 15 6 eret eto eode teet Penis 4 1 5 Audio Inputs and Outputs eese enne enne nennen tenerent eren nee 2 1 6 Tuners and Modulatots 5 cote e eR erret mr eet bee e erem etie ER 6 DO ele TUMORS ior E ROSE EE QU ERE SET RE cede i ety ER EPI 6 1 6 2 Modulators 5 2 iere e e uet Re TO HE RI e ERROR EE eta 6 1 6 3 Radio Erequency ecco oe qtue ie psp Cre ete iU Iit trou Ten 7 1 6 4 Satellite Recetvers 2 etre ert Ree ER Wrap IER 7 UF Video Standards se eO REEF BEC QUI IR IN 7 VB COMMONS esse e oe te b e HER OD A o HE ee aded 9 1 9 Data Unt A neh es ous ce dba sntces castes EEE AE EA E aK ETN 13 1 9 1 Data Format Negotiation sseseseseeeeeeee eren erre nennen nennen nene 14 1 9 2 Image Format Enumeration essere ener nen enne nene 14 1 10 Cropping and Scaling toes esee neo teet otia tiet 15 1 11 Streaming Parameters css ete ien cti cen re eet ee dots eve E EERI 18 2 Tmage r 21 2 1 Standard Image Formats cec eee e erede rene Fees 21 2 2 C olOISpaces c opo ap ORE pete tdi 22 2 3 RGB PFormatssz aeo pA eR QD Qu IU ER RYE 25 DA YU V Eoriniats aeter HR TE RETE HEERD T 27 VAL2 PIX EMT GREY GREY hie cians Pte Sed ees etes 27 VAE2 PIX FMT YUYV YUY WW seca a tie se PO again 28 VAE2 PIX EMT UYNVY UY VY iet neta ebat 29 VAE2 PIX FMT YAIP C YAAP ieiuno eae 30 VAL2 PIX
72. 3 Packed RGB Image Formats Id diizr Byte 0 Byte 1 Byte 2 Byte 3 76543210 76543210 76543210 76543210 Bit 25 Id diir Byte 0 76543210 Bit VAL2 PbxbrMTgRGB 22 ro RGB VAL2 PgXgFMTIRGBST53 ro RGBO VAL2 PEXgFMUIRGBST 3 ro RGBP V4AL2 PIXbrhrbsbPboSxgs RGBQ V4L2_Pbxbribt bRbB 6 8x g3 gt RGBR V4L2_Pbxbrbz bebrb4 bi bo gt BGR3 VAL2 PIKE ML LREBIA TI ro gt RGB3 V4L2_Pbxbrbz bebRbB 2 bi bo BGR4 VAL2 PIXIWNSIRGB 2 r ro RGB4 7 6 Byte 1 543210 b4 bs bz bi bo g4 g3 b4 bs b2 bi bo gs g4 g3 g2 gi go T4 T3 I2 T1 ro g2 gi go r4 T3 r2 ri ro 87 86 85 84 83 82 81 80 87 ge 85 84 83 82 81 80 87 86 85 84 83 82 81 80 87 86 85 84 83 82 81 80 76543210 Chapter 2 Image Formats Byte 2 I7 Yo F5 4 T I2 T1 TO b7 be bs b4 bs b2 bi bo I7 Yo rs r4 r3 I2 r TO b7 be bs b4 bs b2 bi bo Byte 3 76543210 a ale aa Can en as a qoa QE Bit 7 is the most significant bit undefined bit ignored on output random value on input Example 2 2 VAL2 PIX FMT BGR24 4 x 4 pixel image Byte Order Each cell is one byte start 4 0 Bo Go start 4 12 Bio Gio start 4 24 B Gor start 4 36 Bs Go Bo Go Roi Bu Gu Ru Ba Gn Ra Bs Gs Rai Bo Gor Ro Bo Gr Rn B2 Gr Ro Bo Gx Rx Important Drivers may interpret these formats differently Bo Go Ro Bis Gs Re B Gz Rx Bs Gs R3 The v4L2 PIX FMT RGB555 VAL2 PIX FMT RGB565 V4L
73. 8 8 radio B1 G frequendy 8 channel band width MHz Sound 45 45 4 5 5 5 65 5 5 55 465 65 65 carrier 0 001 0 001 5 9996 0 001 0 001 relative c def 0 0005 to vision carrier MHz Notes a Japan uses a standard similar to M NTSC VAL2 STD NTSC M JP b The values in brackets apply to 1 Return Value On success 0 is returned on error 1 and the errno variable is set appropriately EINVAL The struct v412 standard index is out of bounds 89 Notes 1 The supported standards may overlap and we need an unambiguous set to find the current standard returned by VIDIOC_G_STD ioctl VIDIOC G AUDIO VIDIOC S AUDIO Name VIDIOC G AUDIO VIDIOC S AUDIO Query or select the current audio input and its attributes Synopsis int ioctl int fd int request struct v412 audio xargp int ioctl int fd int request const struct v412 audio xargp Arguments fd File descriptor returned by open request VIDIOC G AUDIO VIDIOC S AUDIO argp Description To query the current audio input applications zero out the reserved array of a struct v412 audio and call the vIDIOC G AUDIO ioctl with a pointer to this structure Drivers fill the rest of the structure or return an EINVAL error code when the device has no audio inputs or none which combine with the current video input Audio inputs have one wr
74. A Use in the Title Page and on the covers if any a title distinct from that of the Document and from those of previous versions which should if there were any be listed in the History section of the Document You may use the same title as a previous version if the original publisher of that version gives permission e B List on the Title Page as authors one or more persons or entities responsible for authorship of the modifications in the Modified Version together with at least five of the principal authors of the Document all of its principal authors if it has less than five e C State on the Title Page the name of the publisher of the Modified Version as the publisher D Preserve all the copyright notices of the Document E Add an appropriate copyright notice for your modifications adjacent to the other copyright notices e F Include immediately after the copyright notices a license notice giving the public permission to use the Modified Version under the terms of this License in the form shown in the Addendum below G Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the Document s license notice H Include an unaltered copy of this License e I Preserve the section entitled History and its title and add to it an item stating at least the title year new authors and publisher of the Modified Version as given on the Title Page If there is no section
75. AL2 drivers are implemented as kernel modules loaded manually by the system administrator or automatically when a device is first opened The driver modules plug into the videodev kernel module It provides helper functions and a common application interface specified in this document Each driver thus loaded registers one or more device nodes with major number 81 and a minor number between 0 and 255 Assigning minor numbers to V4L2 devices is entirely up to the system administrator this is primarily intended to solve conflicts between devices The module options to select minor numbers are named after the device special file with a nr suffix For example video nr for dev video video capture devices The number is an offset to the base minor number associated with the device type When the driver supports multiple devices of the same type more than one minor number can be assigned separated by commas gt insmod mydriver o video nr 0 1 radio nr 20 1 In etc modules conf this may be written as alias char major 81 0 mydriver alias char major 81 1 mydriver alias char major 81 64 mydriver o gt options mydriver video_nr 0 1 radio_nr 0 1 gt When an application attempts to open a device special file with major number 81 and minor number 0 1 or 64 load mydriver and the videodev module it depends upon O Register the first two video capture devices with minor number 0 and 1 base number is 0 the first two radio device wit
76. AY V4L2_BUF YPE_VBI_CAPTURE V4L2_BUE YPE_VBI_OUTPUT VA4L2 BUF TYPE PRIVATE BASE VAL2 BUF TYPE PRIVATE In struct v412_fmtdesc a enum v412 buf type field named t ype was added as in struct v412 format As a result the vIDIOC ENUM FBUFFEMT ioctl is no longer needed and was removed These calls can be replaced by VIDIOC_ENUM_FMT with type V4L2 BUF TYPE VIDEO OVERLAY In struct v412 pix format the depth was removed assuming applications recognizing the format are aware of the image depth and others need not know The same rationale lead to the removal of the v4L2 FMT FLAG COMPRESSED flag The VAL2 FMT FLAG SWCONVECOMPRESSED flag was removed because drivers are not supposed to convert image formats in kernel space The VAL2 FMT FLAG BYTESPERLINE flag was redundant applications can set the bytesperline field to zero to get a reasonable default Since also the remaining flags were replaced the 1ags field itself was removed The interlace flags were replaced by a enum v412 field value in a newly added fied field Old flag enum v4I2 field IVAL2 FMT FLAG NOT INTERLACED V4L2 FMT FLAG INTERLACED VAL2 FIELD INTERLACED V4L2 FMT FLAG COMBINED 173 12 13 14 15 16 17 Chapter 6 History Old flag enum v4I2 field VAL2 FMT FLAG TOPFIELD VAL2 FIELD TOP IVAL2 FM
77. Chrom Levels 1 P Chapter 2 Image Formats Chrom Offset Rounding to the nearest integer and clamping to the range 0 255 finally yields the digital color components Y CbCr stored in YUV images Example 2 1 ITU R Rec BT 601 Forward Transformation int ER EG EB int Yi Cb Cr double r g b double yl pb pr int clamp double x int r x x if r lt 0 else if r gt 255 else r ER 255 0 g EG 255 0 b EB 255 0 yl 0 299 x r 0 587 pb 0 169 x r 0 331 pr 0 5 x r 0 419 Yl clamp 219 yl 16 Cb clamp 224 x pb 128 Cr clamp 224 x pr 128 or shorter x yl 0 299 x ER 0 587 x Yl clamp 219 255 0 Cb clamp 224 255 0 Cr clamp 224 255 0 Inverse Transformation int th Cbr Crs int ER EG EB double r g b double yl pb pr int clamp double x color conversion 0 255 x gamma corrected RGB input output 0 255 gt temporaries round to nearest x return 0 return 255 return r g 0 114 xg 305 g 0 081 i 0 114 x EB yl EB yl ER yl 2 2 x 0 114 2 2 0 299 0 255 x gamma pre corrected input output 0 255 gt temporaries 23 round to nearest ok one should prob 1 int r 2 x du t xu return 0 else if r 255 return 255 el
78. D Name VIDIOC_QUERYSTD Sense the video standard received by the current input Synopsis int ioctl int fd int request v412 std id xargp Arguments fd File descriptor returned by open request VIDIOC_QUERYSTD argp Description The hardware may be able to detect the current video standard automatically To do so applications call VIDIOC_QUERYSTD with a pointer to a v4 2_std_id type The driver stores here a set of candidates this can be a single flag or a set of supported standards if for example the hardware can only distinguish between 50 and 60 Hz systems When detection is not possible or fails the set must contain all standards supported by the current video input or output Return Value On success 0 is returned on error 1 and the errno variable is set appropriately 141 ioctl VIDIOC QUERYSTD EINVAL This ioctl is not supported 142 ioctl VIDIOC REQBUFS Name VIDIOC_REQBUEF S Initiate Memory Mapping or User Pointer I O Synopsis int ioctl int fd int request struct v412 requestbuffers argp Arguments fd File descriptor returned by open request VIDIOC REQBUFS argp Description This ioctl is used to initiate memory mapped or user pointer I O Memory mapped buffers are located in device memory and must be allocated with this ioctl before they can be mapped into the application s address space User buffers are allocated by applications themselves an
79. D and are listed in Table 1 1 The ID is used when querying the attributes of a control and when getting or setting the current value Generally applications should present controls to the user without assumptions about their purpose Each control comes with a name string the user is supposed to understand When the purpose is non intuitive the driver writer should provide a user manual a user interface plug in or a driver specific panel application Predefined IDs were introduced to change a few controls programmatically for example to mute a device during a channel switch Drivers may enumerate different controls after switching the current video input or output tuner or modulator or audio input or output Different in the sense of other bounds another default and current value step size or other menu items A control with a certain custom ID can also change name and type Control values are stored globally they do not change when switching except to stay within the reported bounds They also do not change e g when the device is opened or closed when the tuner radio frequency is changed or generally never without application request Since VAL2 specifies no event mechanism panel applications intended to cooperate with other panel applications be they built into a larger application as a TV viewer may need to regularly poll control values to update their user interface Table 1 1 Control IDs ID Type Description V4
80. DE AUTO 3 Namely N PAL Argentina M PAL N PAL and NTSC Japan with numbers 3 6 sic The viDEO TUNER STEREO ON flag indicating stereo reception became V4L2 TUNER SUB STEREO in field rxsubchans This field also permits the detection of monaural and bilingual audio see the definition of struct v412 tuner for details Presently no replacement exists for the VIDEO TUNER RDS ON and VIDEO TUNER MBS ON flags The vibDEO TUNER LOW flag was renamed to VAL2 TUNER CAP LOW in the struct v412 tuner capability field The VIDIOCGFREQ and VIDIOCSFREQ ioctl to change the tuner frequency where renamed to VIDIOC G FREQUENCY and VIDIOC S FREQUENCY They take a pointer to a struct v412 frequency instead of an unsigned long integer 6 1 5 Image Properties VAL2 has no equivalent of the VIDIOCGPICT and VIDIOCSPICT ioctl and struct video picture The following fields where replaced by VAL2 controls accessible with the VIDIOC_QUERYCTRL VIDIOC G CTRL and VIDIOC S CTRL ioctls struct video picture V4L2 Control ID brightness V4L2_CID_BRIGHTNESS hue V4L2_CID_HUE colour V4L2_CID_SATURATION contrast V4L2_CID_CONTRAST whiteness V4L2_CID_WHITENESS The V4L picture controls are assumed to range from 0 to 65535 with no particular reset value
81. Drivers allocating resources at scanning line granularity and first field only data services The comment that both count values will usually be equal is misleading and pointless and has been removed Compatibility Drivers may return EINVAL applications depending on the previous restriction may not function correctly W Restored description of the driver option to return negative start values Existed in the initial revision of this document not traceable why it disappeared in later versions Compatibility Applications depending on the returned start values being positive may not function correctly Clarification on the use of EBUSY and EINVAL in VIDIOC_S_FMT ioctl Added EBUSY paragraph to section Added description of reserved2 previously mentioned only in videodev h Added VAL2 TYPE VBI INPUT and VAL2 TYPE VBI OUTPUT here and in videodev h The first is an alias for the older VAL2 TYPE VBI the latter was missing in videodev h AR 6 2 8 V4L2 Version 0 20 2002 07 25 Added sliced VBI interface proposal 6 2 9 V4L2 in Linux 2 5 46 2002 10 Around October November 2002 prior to an announced feature freeze of Linux 2 5 the API was revised drawing from experience with V4L2 0 20 This unnamed version was finally merged into Linux 2 5 46 1 As specified in Section 1 1 2 drivers must make related device functions available under all minor device numbers 2 The open function requires access mode O_RDWR regardless
82. ERPTR ORY OVERLAY LOL E SMPT V4 1125 Line 2 COLORSPAC US S HDTV x PT V4 HD and mode 2 COLORSPAC rn ER cap EC7 09 V4 broken BT87 2 COLORSPAC 8 extents E BT878 V4 These should be useful EM M 2 COLORSPAC cures E240M 601 E 470 SYS v4 12__COLORSPAC E_470_SYS I know there will be cameras that send this EM_BG Appendix A Video For Linux Two Header File E w N e yono os 1 luma 4 Assume 5 6 a B WN rp 0x80 theorem ca graphics ycbcr U R 601 broadcast NTSC PAL x E170M range 16 253 instead of 16 235 601 extents x So this is unspecified chromaticities and full 0 255 on each of the Y CbCr comp V4L2_COLORSPAC onents E JPEG 182 Appendix A Video For Linux Two Header File For RGB colourspaces this is probably a good start V4L2 COLORSPACE SRGB 8 enum v412 priority VA4L2 PRIORITY UNSET 0 not initialized V4L2_PRIORITY_BACKGROUND 1 V4L2_PRIORITY_INTERACTIVE 2 V4L2_PRIORITY_RECORD 3 V4L2_PRIORITY_DEFAULT V4L2_PRIORITY_INTERACTIVE hi struct v412 rect 832 left 83 2
83. FMT YVUA420 YV12 VAL2 PIX FMT YUVA420 CYUI 31 VAL2 PIX FMT YVUA410 CYVU9 VAL2 PIX FMT YUVA10 YUVO 32 VAL2 PIX FMT YUV422P 422P cessent eene nennen nnne nennen nennen ene 33 V4L2 PIX FMT YUVA P C411 a escena rete 34 V4L2_PIX_FMT_NV12 NV12 V4L2_PIX_FMT_NV21 CNV2I eee 35 2 5 Compressed POrmats sesser ee n E eTe ende he et pertes he ia p EEE Eras EE 36 2 6 Reserved Format Identifiets cuerpo eaei e e le ian 36 3 Input Output aer 37 BV Read Wie ioe cess 37 3 2 Streaming I O Memory Mapping eese ener eene entente 37 3 3 Streaming O User POtDtets endete ette rr eere deo e etuer t ee enero 40 34 Asynchronous UO 5 iE Ae 41 2 9 BUTTOTSS eter eroe rei Are Ee A ie ceu epe eee bap rey eee x yero P Cn 41 3 5 T Timecodes iih tee ehe eene rte ph 45 SM ar Ol 46 iii 4 Device TY Pe p 51 4 1 Video Capture Interface eessssesssseeeese eene ener ethernet enne 51 41 1 Querying Capabilities iret t eerte i ee de 51 4 1 2 Supplemental Functions eseseeeeseeeeeeeeerennenne nennen nennen nennen enne 51 4 1 3 Image Format Negotiation ener etre nennen ennennen nennen 51 4 1 4 Reading Images eese AE E S enhen nennen enne nein 52 4 2 Video Overlay Interface ete eee quatur e ere pete ret edite 52 4 2 1 Querying Capabilities eene enne nene 5
84. Gd A VALE2 read i iue uad gestu e D ER aH e RU WT Qui Oe MAID2 select 5tetietat E E E EE E ete hs tA eh Suus VAT2 WTIMe i tiet S PASE RESI E ENS 5 V4L2 Driver Programming M sitire R 6 1 Differences between V4L and V4AL2 sse nennen eren nen 159 6 1 1 Opening and Closing Devices esesseeeeeeeneeneeeeeneen eere 159 6 1 2 Querying Capabilities eet eee ertet etie 159 6 1 3 Video SOUrceS eee Inepte erai epe cae 161 6 TA Tuning a 5 ere erbe e Ee tmn leue eiie iit 161 6 1 5 Image Properties ke ee IR ai Re i ee S 162 OU EC 6071 CW ne ae eee ere 163 6 1 7 Frame Buffer Overlay sese eneenn enne R REE aan 164 6 1 8 CTODpDIB gi nU y RI E E E ede RE ERU 164 6 1 9 Reading Images Memory Mapping sese 165 6 1 9 1 Capturing using the read method see 165 6 1 9 2 Capturing using memory mapping 165 6 1 10 Reading Raw VBI Data eie ee e AU ei 166 6 111 Miscellaneous enema dne RR 167 6 2 History of the VAL2 APE eraning c te t piede E Ret ceteris 167 6 2 Early Versi0ns os eee E eei RR 167 6 2 2 V4E2 Vers10n 0 1671999 01 3 i i iE ed 168 6 2 3 V4L2 Version 0 18 1999 03 16 sss nennen nennen 168 6 2 4 V4L2 Version 0 19 1999 06 05 cissssssseseeseeeeeeneeeennen nennen eren 168 6 2 5 V4L2 Version 0 20 1999 09 10 cessent nennen 168 6 2 6 V4L2 Version 0 20 incremental chan
85. IDIOC_QBUF ioctl it is always set and after VIDIOC DOBUF always cleared 44 VAL2 BUF FLAG DONE VAL2 BUF FLAG KEYFRAME VAL2 BUF FLAG PFRAME VAL2 BUF F LAG BFRAME VAL2 BUF FLAG TIMECODE V4L2 BUF FLAG INPUT Table 3 4 enum v4l2 memory VAL2 MI VAL2 MI VAL2 MI EMORY USI EMORY OV EMORY MMAP ERPTR ERLAY 3 5 1 Timecodes 0x0004 0x0008 0x0010 0x0020 0x0100 0x0200 Chapter 3 Input Output When this flag is set the buffer is currently on the outgoing queue ready to be dequeued from the driver Drivers set or clear this flag when the VIDIOC_QUERYBUF ioctl is called After calling the VIDIOC_QBUF or VIDIOC_DQBUF it is always cleared Of course a buffer cannot be on both queues at the same time the V4L2_BUF_FLAG_QUEUED and V4L2_BUF_FLAG_DONE flag are mutually exclusive They can be both cleared however then the buffer is in dequeued state in the application domain to say so Drivers set or clear this flag when calling the VIDIOC DOBUF ioctl It may be set by video capture devices when the buffer contains a compressed image which is a key frame or field i e can be decompressed on its own Similar to V4L2_BUF_FLAG_KEYFRAME this flags predicted frames or fields which contain only differences to a previous key frame Similar to V4L2_BUF_FLAG_PFRAME this is a bidirectional predicted frame or
86. IOC S INPUT eerte neret 107 ioctl VIDIOC G JPEGCOMP VIDIOC_S_JPEGCOMP seeeeeeee 109 ioctl VIDIOC G MODULATOR VIDIOC S MODULATOR eene 111 ioctl VIDIOC G OUTPUT VIDIOC S OUTPUT ceteri 114 ioctl VIDIOC G PARM VIDIOC S PARM seeseseeeneeeneenee nemen eene etre 116 ioctl VIDIOC G PRIORITY VIDIOC S PRIORITY eere 120 ioctl VIDIOC G SLICED VBI CAP eero Eer EEEn etre entente trennen E en 122 ioctl VIDIOC G STD VIDIOC S STD eene enne nennen etre 124 ioctl VIDIOC G TUNER VIDIOC S TUNER eere eene 125 ioctl VIDIOC LOG STATUS esses erint eter ete e PE RU pete tiep 129 ioctl VIDIOC OVERLAY iie e he P eg etie dee E Rn 130 ioctl VIDIOC QBUF VIDIOC DOBU K raaes saider aoisi nennen eren enne 131 1octl VIDIOC QUERY BUE 4 iicet on cR tre eis E DR ette Ret tere deis 133 10ctl VIDIOC QUERY CAP netter eere ert HR PP Eee heater 135 ioctl VIDIOC QUERYCTRL VIDIOC QUERYMBNU eene 138 ioctl VIDIOG QUERYSTD teo oser s ore iesi E ea ume epo erede 141 io tl VIDIOC REOBUFS ceee bic een cue t de iecore EEEE AE EEE 143 ioctl VIDIOC_STREAMON VIDIOC_STREAMOFF esee 145 VAEZ mmap s rete rre eve re ueber t a A E N E EEE AE EA E E VAL2 m nmap i inre ea qai ea AT VAEZ opensa ooie ae a e RE AEE EAT Ee Ooa EE GAENE VAL poll 4 antera a e ePi ed aed Ir N
87. IOC S MPEGCOMBDP ce eeeeee eee eee en senate sono seno tatns 94 ioctl VIDIOC G CROP VIDIOC S CRODB ee eeeeeeeeeen eene teet tn en eene toss ens tn sens tasses ense sets 95 ioctl VIDIOC G CTRL VIDIOC S CTRL ee eee cesse ene en ettet ento tn eto stato sens ens ta sesso sense tens 97 ioctl VIDIOC G FBUF VIDIOC S FBUF eeeeeee eee ee eene en setate ene tn eto stato sens ene ta seen sense tens 99 ioctl VIDIOC G FMT VIDIOC S FMT VIDIOC TRY FMT ee eeeeee eee eee eene ene nona 102 ioctl VIDIOC G FREQUENCY VIDIOC S FREQUENTCY eeeeeeeeee eee ee een eene tenen setues 105 ioctl VIDIOC G INPUT VIDIOC S INPUT eee eee eese eene etse teens ene tn eta stato sens tn ette en ne tuea 107 ioctl VIDIOC G JPEGCOMP VIDIOC S JPEGCOMBP eee serene teen etna tn netos etes naso 109 ioctl VIDIOC G MODULATOR VIDIOC S MODULATOR e eee eee ee eee eeo eene toes nota 111 ioctl VIDIOC G OUTPUT VIDIOC S OUTPUT eee eee ee eee ee eee ene tneta ste en seno tn sete sen seines 114 ioctl VIDIOC G PARM VIDIOC S PARM sssscssssssssscsssssscsssssscsecsecssscsscssscssssesssessossesses 116 ioctl VIDIOC G PRIORITY VIDIOC S PRIORITY eres eene eee seen eee tn eene tos tne tees neta 120 ioctl VIDIOC G SLICED VBI CAP enr eso ere obo r t na eta ooa atn ea loa kot ee ba beta Sl nei oen a ete ret
88. It is not defined how the driver writer may achieve that it will depend on the hardware and the ingenuity of the driver writer High quality mode is a different mode from the the regular motion video capture modes In high quality mode The driver may be able to capture higher resolutions than for motion capture The driver may support fewer pixel formats than motion capture e g true color The driver may capture and arithmetically combine multiple successive fields or frames to remove color edge artifacts and reduce the noise in the video data The driver may capture images in slices like a scanner in order to handle larger format images than would otherwise be possible Animage capture operation may be significantly slower than motion capture Moving objects in the image might have excessive motion blur Capture might only work through the read call Return Value On success 0 is returned on error 1 and the errno variable is set appropriately EINVAL This ioctl is not supported 119 ioctl VIDIOC G PRIORITY VIDIOC S PRIORITY Name VIDIOC G PRIORITY VIDIOC S PRIORITY Query or request the access priority associated with a file descriptor Synopsis int ioctl int fd int request enum v412 priority argp int ioctl int fd int request const enum v412 priority xargp Arguments fd File descriptor returned by open request VIDIOC G PRIORITY VIDIOC 5 PRIORITY arg
89. L2 CID BASE First predefined ID equal to V4L2_CID_BRIGHTNESS V4L2_CID_BRIGHTNESS integer Picture brightness or more precisely the black level Will not turn up the intelligence of the program you re watching V4L2_CID_CONTRAST integer Picture contrast or luma gain V4L2_CID_SATURATION integer Picture color saturation or chroma gain V4L2_CID_HUE integer Hue or color balance xj VA4L2 CID AUDIO VOLUM integer Overall audio volume Note some drivers also provide an OSS or ALSA mixer interface Ij V4L2 CID AUDIO BALANCI integer Audio stereo balance Minimum corresponds to all the way left maximum to right V4L2 CID AUDIO BASS integer Audio bass adjustment V4L2 CID AUDIO TREBLE integer Audio treble adjustment V4L2 CID AUDIO MUTE boolean Mute audio i e set the volume to zero however without affecting V4AL2 CID AUDIO VOLUME Like ALSA drivers VAL2 drivers must mute at load time to avoid excessive noise Actually the entire device should be reset to a low power consumption state 10 ID VA4L2 CID AUDIO VAL2 CID BLACK OUDNI EVEL V4L2_CID_AUTO_W HITE V4L2_CID_DO_WHITE_BALANC V4L2_CID_RED_BALANCE V4L2_CID_BLUE_BALANC V4L2_CID_GAMMA ESS V4L2_CID_WHITEN V4L2_CID_EXPOSURE V4L2_CID_AUTOGAI V4L2_CID_GAIN V4L2_CID_HFLIP V4L2_CID_VFLIP V4L2_CID_HCEN
90. MSTD now takes a pointer to a struct v412 standard directly The information which standards are supported by a particular video input or output moved into struct v4I2 input and struct v412 output fields named sta respectively The struct v412 queryctrl fields category and group did not catch on and or were not implemented as expected and therefore removed The VIDIOC_TRY_FMT ioctl was added to negotiate data formats as with VIDIOC S FMT but without the overhead of programming the hardware and regardless of I O in progress In struct v412_ format the fmt union was extended to contain struct v412 window As a result all data format negotiation is now possible with VIDIOC G FMT VIDIOC S FMT and VIDIOC TRY FMT the VIDIOC G WIN VIDIOC S WIN and ioctl to prepare for overlay were removed The type field changed to type enum v4lI2 buf type and the buffer type names changed as follows Old defines enum v4I2 buf type IVAL2 BUF TYPE CAPTURE IVAL2 BUF TYPE VIDEO CAPTURE IVAL2 BUF TYPE CODECIN Preliminary omitted IVAL2 BUF TYPE CODECOUT Preliminary omitted IVAL2 BUF TYPE EFFECTSIN Preliminary omitted IVAL2 BUF TYPE EFFECTSIN2 Preliminary omitted IVAL2 BUF TYPE EFFECTSOUT Preliminary omitted IVAL2 BUF TYPE VIDEOOUT IVAL2 BUF TYPE VIDEO OUTPUT IVAL2 BUF TYPE VIDEO OVERL
91. NER CAP NORM 0x0002 TUNER CAP STEREO 0x0010 UNER CAP LANG2 0x0020 UNER CAP SAP 0x0020 UNER CAP LANGI1 0x0040 Flags for the rxsubchans field define V4L2 define V4L2 define V4L2 define V4L2 define V4L2 TUNER SUB MONO 0x0001 TUNER SUB STEREO 0x0002 TUNER SUB LANG2 0x0004 TUNER SUB SAP 0x0004 UNER SUB LANG1 0x0008 Values for the audmode field define V4L2_ define V4L2 define V4L2 define V4L2 define V4L2 UNER MODE MONO 0x0000 TUNER MODE STEREO 0x0001 TUNER MODE LANG2 0x0002 TUNER MODE SAP 0x0002 UNER MODE LANGI1 0x0003 struct v412 frequency u32 tuner enum v412 tuner type type u32 frequency u32 reserved 8 E x AUDIO struct v412 audio u32 u8 u32 32 2032 index name 32 capability mode reserved 2 194 Appendix A Video For Linux Two Header File Flags for the capability field define V4L2 AUDCAP STEREO 0x00001 define V4L2 AUDCAP AVL 0x00002 Flags for the mode field define V4L2 AUDMODE AVL 0x00001 define V4L2 AUDMODE 32BITS 0x00002 struct v412 audioout u32 index M name 32 u32 capability u32 mode u32 reserved 2 DATA S E R V I C E S VBI Data services API by Michael Schimek x Raw VBI x struct v412
92. O exit EXIT FAILURE 1 6 Tuners and Modulators 1 6 1 Tuners Video input devices can have one or more tuners demodulating a RF signal Each tuner is associated with one or more video inputs depending on the number of RF connectors on the tuner The t ype field of the respective struct v412 input returned by the VIDIOC_ENUMINPUT ioctl is set to V4L2 INPUT TYPE TUNER and its tuner field contains the index number of the tuner Radio devices have exactly one tuner with index zero no video inputs To query and change tuner properties applications use the VIDIOC G TUNER and VIDIOC S TUNER ioctl respectively The struct v412 tuner returned by VIDIOC_G_TUNER also contains signal status information applicable when the tuner of the current video input or a radio tuner is queried Note that VIDIOC S TUNER does not switch the current tuner when there is more than one at all The tuner is solely determined by the current video input Drivers must support both ioctls and set the V4L2 CAP TUNER flag in the struct v412 capability returned by the vIDIOC QUERYCAP ioctl when the device has one or more tuners 1 6 2 Modulators Video output devices can have one or more modulators uh modulating a video signal for radiation or connection to the antenna input of a TV set or video recorder Each modulator is associated with one or more video outputs depending on the number of RF connectors on the modulator The t
93. S 9 1 0 SN9C10x compression 184 Appendix A Video For Linux Two Header File define VA4L2 PIX FMT PWC1 v412 fourcc P W C 1 x pwc older webcam x define VA4L2 PIX FMT PWC2 v412 fourcc P W C 2 pwc newer webcam x FORMA T ENUMERATION x struct v412 fmtdesc u32 index Format number enum v412 buf type type buffer type 32 flags u8 description 32 x Description string x u32 pixelformat Format fourcc u32 reserved 4 he define V4L2 FMT FLAG COMPRESSED 0x0001 TIMECOD x struct v412 timecode cal a 32 type 32 flags us frames gt ug seconds u8 minutes u8 hours u8 userbits 4 Type define V4L2 TC TYPE 24FPS define VA4L2 TC TYPE 25FPS define V4L2 TC TYPE 30FPS C C define V4L2_ YPE 50FPS define VA4L2 TC TYPE 60FPS Qr 0 N F Flags define V4L2 TC FLAG DROPFRAM fl 0x0001 drop frame mode define V4L2 TC FLAG COLORFRAME 0x0002 define V4L2 TC USERBITS field 0x000C define V4L2 TC USERBITS USERDEFINED 0x0000 define V4L2 TC USERBITS 8BITCHARS 0x0008 The above is based on SMPTE timecodes if 1 MPEG COMPRES SL ON PARAME T R S x WARNING this is still work in progress right now most likely x HF there will be some incompatible chang
94. S 0x0400 VPS gt PAL line 16 Byte number 3 to 15 according to Figure 9 of ETS 300 231 Isb first transmitted V4L2_SLICED_CAPTIONDXIHH0 EIA608 gt NTSC line 21 284 Two bytes in second field 21 transmission order including parity bit lsb first transmitted V4L2 SLICED WSS 6250x4000 WSS gt PAL SECAM line 23 Byte 0 1 msb lsb msb Bat 7 65 4 3 2 1 0 x x 53 12 V4L2_SLICED_VBI_5230x1000 Set of services applicable to 525 line systems V4L2_SLICED_VBI_ 6210x4401 Set of services applicable to 625 line systems Drivers may return an EINVAL error code when applications attempt to read or write data without prior format negotiation after switching the video standard which may invalidate the negotiated VBI parameters and after switching the video input which may change the video standard as a side effect The VIDIOC_S_FMT ioctl may return an EBUSY error code when applications attempt to change the format while i o is in progress between a VIDIOC STREAMON and VIDIOC STREAMOFF call and after the first read or write call 4 7 4 Reading and writing sliced VBI data A single read or write call must pass all data belonging to one video frame That is an array of v412 sliced vbi data structures with one or more elements and a total size not exceeding io size bytes Likewise in streaming I O mode one buffer of io size bytes must contain data of one video frame The id of unused v412 sliced vbi data eleme
95. S1 L2 S1 D PAL B D PAL Bl D PAL G D PAL H D PAL I D PAL D D PAL D1 D PAL K D PAL M D PAL N D PAL Nc D PAL 60 SC M SC M JP SC 443 ECA ECA ECA ECA Ww ungo vow ECA ECAM K1 ECA ATSC HDTV Oc Jg pue JG t NNNnNnNNNN WN ECA iC L2_S SC_8_VSB L2_S common L2_S1 L2 S1 12 53 SC 16 VSB D PAL BG I needed stuff O type es Appendix A Video For Linux Two Header File pixelaspect STANDARD lt s lt sss lt lt 4 SB op a Os WW a lt lt NS is sss lt s lt B oS Ww a a E qe sks E L n SUE zd DE Red RP DT Ioue dp se ke ip NO N90 N29 PO PO PSP PK Q0 0o0o0000un au Q0 000000 0 0x0000 0x0000 0x0000 0x0000 0x0000 0x0000 0x0000 0x0000 0x0000 0x0000 0x0000 0x0000 td id 0x0000 td id 0x0000 0x0001 0x0002 0x0004 0x0008 td id 0x0100 std id 0x0200 VAL2 STD PAL B VAL2 STD PAL Bl VAL2 STD PAL G VAL2 STD PAL D VAL2 STD PAL Dl VAL2 STD PAL K VAL2 STD PAL BG VAL2 STD PAL DK VAL2 STD PAL H VAL2 STD PAL I 0001 0002 0004 0008 0010 0020 0040 0080 0100 0200 0400 0800 1000 td id 0x00002000 4000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 190 define V4 define V4 define V4 define define define
96. T if 1 ioctl fd VIDIOC G FMT amp format perror VIDIOC G FMT exit EXIT FAILURE hscale format fmt pix width double crop c width vscale format fmt pix height double crop c height aspect cropcap pixelaspect numerator double cropcap pixelaspect denominator aspect aspect hscale vscale Aspect corrected display size x dwidth format fmt pix width aspect dheight format fmt pix height 1 11 Streaming Parameters Streaming parameters are intended to optimize the video capture process as well as I O Presently applications can request a high quality capture mode with the vIDIOC S PARM ioctl The current video standard determines a nominal number of frames per second If less than this number of frames is to be captured or output applications can request frame skipping or duplicating on the driver side This is especially useful when using the read or write which are not augmented by timestamps or sequence counters and to avoid unneccessary data copying Finally these ioctls can be used to determine the number of buffers used internally by a driver in read write mode For implications see the section discussing the read function To get and set the streaming parameters applications call the vIDIOC G PARM and VIDIOC S PARM ioctl respectively They take a pointer to a struct v412_streamparm which contains a union holding separate parameters for input and
97. T FLAG ODDFIELD VAL2 FMT FLAG BOTFIELD VAL2 FIELD BOTTOM VAL2 FMT FLAG EVENFIELD V4L2_FIELD_SEQ_TB VAL2 FIELD SEQ BT es V4L2 FIELD ALTERNATE The color space flags were replaced by a enum v412 colorspace value in a newly added colorspace field where one of V4L2_COLORSPACE_SMPTE170M VAL2 COLORSPACE BT878 V4L2 COLORSPACE 470 SYSTEM MOr VAL2 COLORSPACE 470 SYSTEM BGreplaces V4AL2 FMT CS 601YUV In struct v412 requestbuffers the type field was properly typed as enum v412 buf type Buffer types changed as mentioned above A new memory field of type enum v4l2 memory was added to distinguish between mapping methods using buffers allocated by the driver or the application See Chapter 3 for details In struct v412 buffer the type field was properly typed as enum v412 buf type Buffer types changed as mentioned above A field field of type enum v412 field was added to indicate if a buffer contains a top or bottom field the field flags were removed Realizing the efforts to introduce an unadjusted system time clock failed the t imest amp field changed back from type stamp t an unsigned 64 bit integer expressing time in nanoseconds to struct timeval With the addition of a second memory mapping method the o set field moved into union m and a new memory field of type enum v4l2 memory was
98. TEXOxO901 TELETEXTPAL SECAM line 7 22 Last 42 of the 45 byte Teletext System B 320 335 second field Teletext packet that is 7 22 without clock run in and framing code lsb first transmitted V4L2_SLICED_VPS 0x0400 VPS gt PAL line 16 Byte number 3 to 15 according to Figure 9 of ETS 300 231 Isb first transmitted V4L2_SLICED_CAPTIONDXI H0 EIA608 gt NTSC line 21 284 Two bytes in second field 21 transmission order including parity bit lsb first transmitted V4L2_SLICED_WSS_ 6250x4000 WSS gt PAL SECAM line 23 Byte 0 1 msb lsb msb Bit 7675 4 3 2 L 0 X x 13 12 V4L2_SLICED_VBI_5230x1000 Set of services applicable to 525 line systems V4L2_SLICED_VBI_ 6200x4401 Set of services applicable to 625 line systems Return Value On success 0 is returned on error 1 and the errno variable is set appropriately EINVAL The device does not support sliced VBI capturing or output 123 ioctl VIDIOC G STD VIDIOC S STD Name VIDIOC G STD VIDIOC S STD Query or select the video standard of the current input Synopsis int ioctl int fd int request v412 std id xargp int ioctl int fd int request const v412 std id argp Arguments fd File descriptor returned by open request VIDIOC G STD VIDIOC S STD argp Description To query and select the current video standard applications use the viDIOC G STD and VIDIOC S STD ioctls which take a pointer to a v412 std id type as argument vIDIOC G STD ca
99. TTV driver sampling rate 28636363 Hz NTSC precisely all 525 line standards 35468950 Hz PAL and SECAM 625 line offset samples_per_line 2048 sample_format V4L2_PIX_FMT_GREY The last four bytes machine endianess integer contain a frame counter start 10 273 NTSC 22 335 PAL and SECAM count 16 16a flags 0 Notes a Old driver versions used different values eventually the custom BTTV VBISIZE ioctl was added to query th Undocumented in the V4L specification in Linux 2 3 the VIDIOCGVBIFMT and VIDIOCSVBIFMT ioctls using struct vbi_format were added to determine the VBI image parameters These ioctls are only partially compatible with the V4L2 VBI interface specified in Section 4 6 gt An offset field does not exist sample_format is supposed to be VIDEO_PAL RAW here ETTE equivalent to V4L2_P1X_FMT_GREY The remaining fields are probably equivalent to struct v4I2 vbi format Apparently only the Zoran ZR 36120 driver implements these ioctls The semantics differ from those specified for V4L2 in two ways The parameters are reset on open and VIDIOCSVBIFMT 166 Chapter 6 History always returns the EINVAL error code if the parameters are invalid 6 1 11 Miscellaneous V4L2 has no equivalent of the VIDIOCGUNIT ioctl Applications can find the VBI device associated with a video capture device or vice versa by reopening the device an
100. The select or poll function are always available To start and stop capturing or output applications call the VIDIOC_STREAMON and VIDIOC STREAMOFF ioctl Note VIDIOC STREAMOFF removes all buffers from both queues as a side effect Since there is no notion of doing anything now on a multitasking system if an application needs to synchronize with another event it should examine the struct v412 buffer timestamp of captured buffers or set the field before enqueuing buffers for output Drivers implementing memory mapping I O must support the VIDIOC_REQBUFS VIDIOC QUERYBUF VIDIOC OBUF VIDIOC DOBUF VIDIOC_STREAMON and VIDIOC_STREAMOFF ioctl the mmap munmap select and poll function capture example 3 3 Streaming I O User Pointers Input and output devices support this I O method when the v4L2_CAP_STREAMING flag in the capabilities field of struct v412_capability returned by the VIDIOC_QUERYCAP ioctl is set If the particular user pointer method not only memory mapping is supported must be determined by calling the VIDIOC_REQBUFS ioctl This I O method combines advantages of the read write and memory mapping methods Buffers are allocated by the application itself and can reside for example in virtual or shared memory Only pointers to data are exchanged these pointers and meta information are passed in struct v412 buffer The driver must be switched into user pointer I O mode by call
101. UERYCAP At least one of the read write streaming or asynchronous I O methods must be supported VBI devices may or may not have a tuner or modulator 4 6 2 Supplemental Functions VBI devices shall support video input or output tuner or modulator and controls ioctls as needed The video standard ioctls provide information vital to program a VBI device therefore must be supported 57 Chapter 4 Device Types 4 6 3 Raw VBI Format Negotiation Raw VBI sampling abilities can vary in particular the sampling frequency To properly interpret the data V4L2 specifies an ioctl to query the sampling parameters Moreover to allow for some flexibility applications can also suggest different parameters As usual these parameters are not reset at open time to permit Unix tool chains programming a device and then reading from it as if it was a plain file Well written V4L2 applications should always ensure they really get what they want requesting reasonable parameters and then checking if the actual parameters are suitable To query the current raw VBI capture parameters applications set the t ype field of a struct v412 format to V4AL2 BUF TYPE VBI CAPTURE or V4L2 BUF TYPE VBI OUTPUT and call the viDIOC G FMT ioctl with a pointer to this structure Drivers fill the struct v412 vbi format vbi member of the mt union To request different parameters applications set the type field of a struct v412 format as above an
102. Video Capture Example mainloop void unsigned int count count 100 while count gt 0 for fd set fds struct timeval tv rnc r FD ZERO amp fds FD SET fd amp fds Timeout x tv tv sec 2 tv tv usec 0 r select fd 1 amp fds NULL NULL amp tv if 1 r if EINTR errno continue errno exit select if 0 r fprintf stderr select timeout n exit EXIT_FAILURE if read_frame break EAGAIN continue select loop static void stop capturing enum v412_buf_type type io ETHOD_R switch case IO M EAD x Nothing to do break void 203 Appendix B Video Capture Example case IO METHOD MMAP case IO METHOD USERPTR type V4L2 BUF TYPE VIDEO CAPTURE if 1 xioctl fd VIDIOC STREAMOFF amp type errno exit VIDIOC STREAMOFF break static void start_capturing void unsigned int i enum v412_buf_type type switch io case IO_METHOD_READ Nothing to do break case IO METHOD MMAP for i 5 0r 2 n buffers i struct v412 buffer buf CLEAR buf buf type VA4L2 BUF TYPE VIDEO CAPTURE buf memory VA4L2 MEMORY MMAP buf index i if 1 xioctl fd VIDIOC_QBUF amp buf errno exit VIDIOC OQBUF
103. Video for Linux Two API Specification Draft 0 12 Michael H Schimek mschimek 2gmx at Bill Dirks Hans Verkuil Video for Linux Two API Specification Draft 0 12 by Michael H Schimek Bill Dirks and Hans Verkuil Copyright 1999 2000 2001 2002 2003 2004 2005 2006 Bill Dirks Michael H Schimek Hans Verkuil This document is copyrighted O 1999 2006 by Bill Dirks Michael H Schimek and Hans Verkuil Permission is granted to copy distribute and or modify this document under the terms of the GNU Free Documentation License Version 1 1 or any later version published by the Free Software Foundation with no Invariant Sections with no Front Cover Texts and with no Back Cover Texts A copy of the license is included in the appendix entitled GNU Free Documentation License Programming examples can be used and distributed without restrictions Revision History Revision 0 12 2006 02 03 Revised by mhs Corrected the description of struct v412_captureparm and v412_outputparm Revision 0 11 2006 01 27 Revised by mhs Improved the description of struct v412 tuner Revision 0 10 2006 01 10 Revised by mhs VIDIOC G INPUT and VIDIOC S PARM clarifications Revision 0 9 2005 11 27 Revised by mhs Improved the 525 line numbering diagram Hans Verkuil and I rewrote the sliced VBI section He also contributed VIDIOC LOC Revision 0 8 2004 10 04 Revised by mhs Somehow a piece of junk slipped into the capture example removed Revi
104. Y 10 start 16 Y o start 4 24 Y 30 Color Sample Location Ww N Cc i em Cboo Cbio Cboo Cb30 Q0000 Y oi Y u Yazi Y 31 KAM Croo Crio Cro Cro Y o Yn Y 2 Y Cbo Cbi Cboi Cbs KAN Y o3 Y 13 Y 23 Y 33 Croi Cru Cri Cri Q aO OO 28 Mu uuo VAL2 PIX FMT UYVY UYVY Name V4L2 PIX FMT UYVY Variation of VAL2 PIX FMT YUYV With different order of samples in memory Description In this format each four bytes is two pixels Each four bytes is two Y s a Cb and a Cr Each Y goes to one of the pixels and the Cb and Cr belong to both pixels As you can see the Cr and Cb components have half the horizontal resolution of the Y component Example 2 1 vaAL2 PIX FMT UYVY 4 x 4 pixel image Byte Order Each cell is one byte start 4 0 Cboo Y oo Croo Y oi Cbo Y o Croi Y o start 4 8 Cbio Y 10 Crio Yu Cbi Yr Cri Yu start 4 16 Cboo Y o Cr2o Yn Cboi Y Cra Y start 4 24 Cb30 Y 30 Cr3o Yar Cbs31 Y Crs1 Ys Color Sample Location Ww N Cc KKK KO CY e 0 KKK KR KKK KN OnE Ase KK KK 29 V4L2 PIX FMT Y41P Y41P Name VA4L2 PIX FMT Y41P Packed format with 4 horizontal chroma resolution also known as YUV 4 1 1 Description In this format each 12 bytes is eight pixels In the twelve bytes are two CbCr pairs and eight Y s The first CbCr pair goes with the first four Y s and the second CbCr pair goes with the
105. YPE VIDEO CAPTURE When the application calls the VIDIOC_G_FMT ioctl with a pointer to this structure the driver fills the respective member of the mt union In case of video capture devices that is the struct v412 pix format pix member When the requested buffer type is not supported drivers return an EINVAL error code To change the current format parameters applications initialize the t ype field and all fields of the respective mt union member For details see the documentation of the various devices types in Chapter 4 Good practice is to query the current parameters first and to modify only those parameters not suitable for the application When the application calls the VIDIOC_S_FMT ioctl with a pointer to a v412 format structure the driver checks and adjusts the parameters against hardware abilities Drivers should not return an error code unless the input is ambiguous this is a mechanism to fathom device capabilities and to approach parameters acceptable for both the application and driver On success the driver may program the hardware allocate resources and generally prepare for data exchange Finally the VIDIOC_S_FMT ioctl returns the current format parameters as VIDIOC G FMT does Very simple inflexible devices may even ignore all input and always return 102 ioctl VIDIOC G FMT VIDIOC S FMT VIDIOC TRY FMT the default parameters However all VAL2 devices exchanging data with the application must implement
106. able by beginning at index zero and incrementing by one until EINVAL is returned Table 1 struct v412_fmtdesc u32 index Number of the format in the enumeration set by the application This is in no way related to the pixelformat field enum v4 2 buf type type Type of the data stream set by the application Only these types are valid here VAL2 BUF TYPE VIDEO CAPTURE VA4L2 BUF TYPE VIDEO OUTPUT V4L2 BUF TYPE VIDEO OVERLAY and custom driver defined types with code V4L2 BUF TYPE PRIVATE and higher u32 flags See Table 2 gt u8 description 32 Description of the format a NUL terminated ASCII string This information is intended for the user for example YUV 4 2 2 79 ioctl VIDIOC ENUM FMT u32 pixelformat The image format identifier This is a four character code as computed by the v412_fourcc macro define v412 fourcc a b c d __u32 a lt lt 0 __u32 b 8 u32 c 16 __u32 u32 reserved 4 Reserved for future extensions Drivers must set the array to zero Table 2 Image Format Description Flags V4L2 FMT FLAG COMPRESSED 0x0001 This is a compressed format Return Value On success 0 is returned on error 1 and the errno variable is set appropriately EINVAL The struct v412_fmtdesc type is not supported or the index is out of bounds 80 ioctl VIDIOC ENUMINPUT Name VIDIOC ENUMINPUT Enum
107. added to distinguish between mapping methods See Chapter 3 for details The v4L2 BUF REO CONTIG flag was used by the VAL compatibility layer after changes to this code it was no longer needed The v4 2 BUF ATTR DEVICEMEM flag would indicate if the buffer was indeed allocated in device memory rather than DMA able system memory It was barely useful and so has been removed In struct v412 framebuffer the base 3 array anticipating double and triple buffering in off screen video memory however without defining a synchronization mechanism was replaced by a single pointer The v4L2 FBUF CAP SCALEUP and V4L2 FBUF CAP SCALEDOWN flags were removed Applications can determine this capability more accurately using the new cropping and scaling interface The v4L2 FBUF CAP CLIPPING flag was replaced by VAL2 FBUF CAP LIST CLIPPING and V4L2 FBUF CAP BITMAP CLIPPING In struct v412 clip the x y width and height field moved into a c substructure of type struct v412 rect The x and y field were renamed to 1eft and top i e offsets to a context dependent origin In struct v412 window the x y width and height field moved into a w substructure as above A field field of type ov4I2 field was added to distinguish between field and frame interlaced overlay The digital zoom interface including struct v412_zoomcap struct v412 zoom VAL2 ZOOM NONCAP and V4L2 ZOOM WHILESTREAMING was replaced by a new cropping an
108. adding is exactly as long as one Y row including padding Example 2 1 VAL2 PIX FMT YUV411P 4 x 4 pixel image Byte Order Each cell is one byte start 0 Y oo Y a Y o Y os start 4 Y 10 Yu Y a Y is start 8 Y 20 Y n Y n Y a start 12 Y 30 Y a Y a Y ss start 4 16 Cboo start 17 Cbio start 4 18 Cboo start 4 19 Cb30 start 20 Croo start 21 Crio start 22 Cr2o start 23 Cr3o Color Sample Location W N e O KKK KO KKK KR A OAA KKK RS 34 KKK K V4L2 PIX FMT NV12 NV12 V4AL2 PIX FMT NV21 NV21 Name V4L2_PIX_FMT_NV12 V4L2_PIX_FMT_NV21 Formats with horizontal and vertical chroma resolution also known as YUV 4 2 0 One luminance and one chrominance plane with alternating chroma samples as opposed to V4L2_P1X_FMT_YVU420 Description These are two plane versions of the YUV 4 2 0 format The three components are separated into two sub images or planes The Y plane is first The Y plane has one byte per pixel For V4L2_P1X_FMT_NV12 a combined CbCr plane immediately follows the Y plane in memory The CbCr plane is the same width in bytes as the Y plane and of the image but is half as tall in pixels Each CbCr pair belongs to four pixels For example Cb Cr belongs to Y Yor Y 19 Y V4L2_P1X_FMT_NV21 is the same except the Cb and Cr bytes are swapped the CrCb plane starts with a Cr byte If the Y plane has pad bytes after each row then the CbCr plane
109. ap define VIDIOC G CROP _IOWR V 59 struct v412 crop define VIDIOC S CROP _IOW V 60 struct v412 crop define VIDIOC G JPEGCOMP _IOR V 61 struct v412 jpegcompression define VIDIOC S JPEGCOMP IOW V 62 struct v412 jpegcompression define VIDIOC QUERYSTD _IOR V 63 v412 std id define VIDIOC TRY FMT _IOWR V 64 struct v412 format define VIDIOC ENUMAUDIO _IOWR V 65 struct v412 audio define VIDIOC ENUMAUDOUT _IOWR V 66 struct v412_audioout define VIDIOC G PRIORITY _IOR V 67 enum v412 priority define VIDIOC S PRIORITY _IOW V 68 enum v412 priority if 1 KEEP define VIDIOC G SLICED VBI CAP IOR V 69 struct v412 sliced vbi cap endif define VIDIOC LOG STATUS lO V 70 for compatibility will go away some day define VIDIOC OVERLAY OLD _IOWR V 14 int define VIDIOC S PARM OLD IOW V 22 struct v412 streamparm define VIDIOC S CTRL OLD _ TOW V 28 struct v4l2 control define VIDIOC G AUDIO OLD _IOWR V 33 struct v412 audio define VIDIOC G AUDOUT OLD _IOWR V 49 struct v412 audioout define VIDIOC CROPCAP OLD IOR V 58 struct v412 cropcap define BASE VIDIOC PRIVATE 192 192 255 are private x ifdef KERNEL V4 L2 DRIVER H LPER APTI Some commonly needed functions for drivers v412 common o module include lt linux fs h gt Video standard functions extern unsigned int v412 video std fps struct v412 standard v
110. apture device n dev name exit EXIT FAILURE switch io case IO METHOD READ if cap capabilities amp V4L2 CAP READWRITE fprintf stderr s does not support read i o n dev name exit EXIT FAILURE break case IO METHOD MMAP case IO METHOD USERPTR if cap capabilities amp V4L2 CAP STREAMING fprintf stderr s does not support streaming i o n dev name exit EXIT FAILURE break Select video input video standard and tune here x CLEAR cropcap cropcap type VA4L2 BUF TYPE VIDEO CAPTURE if 0 xioctl fd VIDIOC CROPCAP amp cropcap crop type V4L2 BUF TYPE VIDEO CAPTURE crop c cropcap defrect reset to default if 1 xioctl fd VIDIOC S CROP amp crop switch errno case EINVAL Cropping not supported break default Errors ignored break else Errors ignored CLEAR fmt 208 fmt fmt fmt fmt fmt if Note VIDIOC S FMT may change width and height Buggy driver paranoia min if min TIE swit case case case static void close_device Lf static void open_device Appendix B Video Capture Example type V4L2_BUF_TYPE_VIDEO_CAPTURE fmt pix width 640 fmt pix height 480 fmt p
111. at named pix of its For more information about the V4L2 read interface see Section 3 1 6 1 9 2 Capturing using memory m apping Applications can read from VAL devices by mapping buffers in device memory or more often just buffers allocated in DMA able system memory into their address space This avoids the data copy overhead of the read method V4L2 supports memory mapping as well with a few differences V4L V4L2 The image format must be selected before buffers are allocated with the VIDIOC_S_FMT ioctl When no format is selected the driver may use the last possibly by another application requested format allocated The number is built into the driver unless it has a module option to change the number when the driver module is loaded Applications cannot change the number of buffers The VIDIOC_REQBUEFS ioctl allocates the desired number of buffers this is a required step in the initialization sequence Drivers map all buffers as one contiguous range o memory The VIDIOCGMBUF ioctl is available to query the number of buffers the offset of each buffer from the start of the virtual file and the overall amount of memory used which can be used as arguments to the mmap function fBuffers are individually mapped The offset and size of each buffer can be determined with the VIDIOC QUERYBUF ioctl 165 Chapter 6 History V4L V4L2 The VIDIOCMCAPTURE ioctl prepare
112. audio when the input has more channels a down mix of channel 1 and 2 This flag does not combine with V4L2_TUNER_SUB_STEREO or V4L2_TUNER_SUB_LANG1 Modulate channel 1 and 2 as left and right channel of a stereo audio signal When the input has only one channel or two channels and V4L2 TUNER SUB SAP is also set channel 1 is encoded as left and right channel This flag does not combine with vV4L2 TUNER SUB MONO or V4L2 TUNER SUB LANGI When the driver does not support stereo audio it shall fall back to mono 112 V4AL2 TUN ER SUB LANG1 UN VAL2 VAL2 ER SUB LANG2 UNI ER SUB SAP Return Value ioctl VIDIOC G MODULATOR VIDIOC S MODULATOR 0x0008 0x0004 0x0004 Modulate channel 1 and 2 as primary and secondary language of a bilingual audio signal When the input has only one channel it is used for both languages It is not possible to encode the primary or secondary language only This flag does not combine with V4L2 TUNER SUB MONO or V4L2 TUNER SUB STEREO If the hardware does not support the respective audio matrix or the current video standard does not permit bilingual audio the vIDIOC S MODULATOR ioctl shall return an EINVAL error code and the driver shall fall back to mono or stereo mode Same effect as VAL2 TUNER SUB LANGI When combined with vV4L2 TUNER SUB MONO the first channel is encoded as mono audio
113. awing operations or windows moving or changing their stacking order To combine the advantages of Xv and V4L a special Xv driver exists in XFree86 just programming any overlay capable Video4Linux device it finds To enable it etc X11 XF86Config must contain these lines Section Module Load v41 EndSection As of XFree86 4 2 this driver still supports only VAL ioctls however it should work just fine with all V4L2 devices through the V4L2 backward compatibility layer Since V4L2 permits multiple opens it is possible if supported by the V4L2 driver to capture video while an X client requested video overlay Restrictions of simultaneous capturing and overlay mentioned in Section 4 2 apply Only marginally related to V4L2 XFree86 extended Xv to support hardware YUV to RGB conversion and scaling for faster video playback and added an interface to MPEG 2 decoding hardware This can be used to improve displaying captured images 6 3 2 Digital Video VAL2 does not at this time and possibly never support digital terrestrial cable or satellite broadcast A separate project aiming at digital receivers exists You can find its homepage at http linuxtv org This group found the requirements sufficiently different from analog television to choose independent development of their interfaces 6 3 3 Audio Interfaces to do OSS ALSA Notes 1 This is not implemented in XFree86 178 Appendix A Video For Linux Two Header File
114. bi data u32 5032 2032 02032 u8 i fendif x AGGR x Appendix A Video For Linux Two Header File must be zero x standards id field 0 first fie line 1 23 x reserved must be 0 x data 48 EGA E ST R U G TURE S struct v412 format Stream data format enum v412_buf_type type union if 1 KEEP endif fmt struct Struct struct struct u8 v412 pix format v412 window v412 vbi format v412 sliced vbi format raw data 200 Stream type dependent parameters ld Ls pix win vbi sliced VAL2 VAL2 VAL2 N4L2 0x0001 0x0400 0x1000 0x4000 VAL2 SLICED CAPTION 525 V4L2_SLICED_TELETEXT_B specifies lines 0 23 1 23 used specifies lines 0 23 1 23 used V4L2_SLICED_VPS V4L2 of the first field of the second field equals frame lines 313 336 for 625 line video second field 263 286 for 525 line standards BUF_TYPE_VIDEO_CAPTURE BUF_TYPE_VIDEO_OVERLAY BUF_TYPE_VBI_CAPTURE BUF_TYPE_SLICED_VBI_CAP user defined 196 struct v412 streamparm enum v412_buf_type type Appendix A Video For Linux Two Header File output user defined
115. bit integer and I will change the v412 masterclock gettime function used only by drivers to return a 64 bit integer oo The sequence field is added to the struct v412 buffer The sequence field indicates which frame this is in the sequence 0 1 2 3 4 etc Set by capturing devices Ignored by output devices If a capture driver drops a frame the sequence number of that frame is skipped A break in the sequence will indicate to the application which frame was dropped 6 2 6 V4L2 Version 0 20 incremental changes 1999 12 23 In struct v412 vbi format field reserved1 became offset Previously reservedi was required to always read zero 2000 01 13 Added VAL2 FMT FLAG NOT INTERLACED 2000 07 31 Included linux poll h in videodev h for compatibility with the original videodev h 2000 11 20 Added VAL2 TYPE VBI OUTPUT Added VAL2 PIX FMT YA41P 2000 11 25 Added VAL2 TYPE VBI INPUT 2000 12 04 Fixed a couple typos in symbol names 2001 01 18 Fixed a namespace conflict the fourcc macro changed to v412_fourcc 2001 01 25 Fixed a possible driver level compatibility problem between the original 2 4 0 videodev h and the videodev h that comes with videodevX If you were using an earlier version of videodevX on 2 4 0 then you should recompile your v4l and V4L2 drivers to be safe 2001 01 26 videodevX Fixed a possible kernel level incompatibility between the videodevX videodev h and the 2 2 x videodev h that had the devfs patche
116. bounds EBUSY The control is temporarily not changeable possibly because another applications took over control of the device function this control belongs to 98 ioctl VIDIOC G FBUF VIDIOC S FBUF Name VIDIOC G FBUF VIDIOC S FBUF Get or set frame buffer overlay parameters Synopsis int ioctl int fd int request struct v412 framebuffer xargp int ioctl int fd int request const struct v412 framebuffer xargp Arguments fd File descriptor returned by open request VIDIOC_G_FBUF VIDIOC S FBUF argp Description The VIDIOC_G_FBUF and VIDIOC S FBUF ioctl are used to get and set the frame buffer parameters for video overlay To get the current parameters applications call the VIDIOC_G_FBUF ioctl with a pointer to a v4l2_framebuffer structure the driver fills all fields of the structure or returns the EINVAL error code when overlay is not supported To set the parameters applications initialize the flags field base unless the overlay is of VAL2 FBUF CAP EXTERNOVERLAY type and the struct v412 pix format fmt substructure The driver accordingly prepares for overlay or returns an error code When the driver does not support VAL2 FBUF CAP EXTERNOVERLAY i e it will write into video memory the VIDIOC S FBUF ioctlis a privileged function and only the superuser can change the frame buffer parameters Table 1 struct v412_framebuffer u32 capability Overlay capabili
117. d 110 ioctl VIDIOC G MODULATOR VIDIOC S MODULATOR Name VIDIOC G MODULATOR VIDIOC S MODULATOR Get or set modulator attributes Synopsis int ioctl int fd int request struct v412 modulator xargp int ioctl int fd int request const struct v412 modulator xargp Arguments fd File descriptor returned by open request VIDIOC G MODULATOR VIDIOC 5 MODULATOR argp Description To query the attributes of a modulator applications initialize the index field and zero out the reserved array of a struct v412 modulator and call the VIDIOC_G_MODULATOR ioctl with a pointer to this structure Drivers fill the rest of the structure or return an EINVAL error code when the index is out of bounds To enumerate all modulators applications shall begin at index zero incrementing by one until the driver returns EINVAL Modulators have two writable properties an audio modulation set and the radio frequency To change the modulated audio subprograms applications initialize the index and txsubchans fields and the reserved array and call the vIDIOC S MODULATOR ioctl Drivers may choose a different audio modulation if the request cannot be satisfied However this is a write only ioctl it does not return the actual audio modulation selected To change the radio frequency the vib1OC S FREQUENCY ioctl is available 111 ioctl VIDIOC G MODULATOR VIDIOC S MODULATOR Table 1 struct v4l2 modulator u32 index u8
118. d initialize all fields of the struct v412 vbi format vbi member of the fmt union or better just modify the results of vIDIOC G FMT and call the viproc s rwr ioctl with a pointer to this structure Drivers return an EINVAL error code only when the given parameters are ambiguous otherwise they modify the parameters according to the hardware capabilites and return the actual parameters When the driver allocates resources at this point it may return an EBUSY error code to indicate the returned parameters are valid but the required resources are currently not available That may happen for instance when the video and VBI areas to capture would overlap or when the driver supports multiple opens and another process already requested VBI capturing or output Anyway applications must expect other resource allocation points which may return EBUSY at the VIDIOC_STREAMON ioctl and the first read write and select call VBI devices must implement both the VIDIOC_G_FMT and VIDIOC S FMT ioctl even if VIDIOC_S_FMT ignores all requests and always returns default parameters as VIDIOC_G_FMT does VIDIOC_TRY_FMT is optional Table 4 4 struct v412_vbi_format u32 sampling rate Samples per second i e unit 1 Hz u32 offset Horizontal offset of the VBI image relative to the leading edge of the line synchronization pulse and counted in samples The first sample in the VBI image will be located offset sampling rate seconds following the leadin
119. d scaling interface The previously unused struct v412_cropcap and v412 crop where redefined for this purpose See Section 1 10 for details 174 Chapter 6 History 18 In struct v412 vbi format the SAMPLE FORMAT field now contains a four character code as used to identify video image formats vVAL2 PIX FMT GREY replaces the VAL2 VBI SF UBYTE define The reserved field was extended 19 In struct v412 captureparm the type of the t imeperframe field changed from unsigned long to struct v412_fract A new field readbuffers was added to control the driver behaviour in read I O mode According changes were made to struct v412_outputparm 20 The struct v412 performance and vibioc G PERF ioctl were dropped Except when using the read write I O method which is limited anyway this information is already available to the application 21 The example transformation from RGB to YCbCr color space in the old VAL2 documentation was inaccurate this has been corrected in Chapter 2 gt 6 2 10 V4L2 2003 06 19 1 A new capability flag v4L2_CAP_RADIO was added for radio devices Prior to this change radio devices would identify soley by having exactly one tuner whose type field reads V4L2_TUNER_RADIO 2 An optional priority mechanism was added see Section 1 3 gt for details 3 The audio input and output interface was found to be incomplete Previously the viDIOC G AUDIO ioctl would enumerate the available audio inpu
120. d call the VIDIOC QUERYMENU ioctl with a pointer to this structure The driver fills the rest of the structure or returns an EINVAL error code when the id or index is invalid Menu items are enumerated by calling VIDIOC QUERYMENU with successive index values from struct v412_queryctrl minimum 0 to maximum inclusive Table 1 struct v4I2 queryctrl 138 u32 enum v412 ctrl type u8 32 832 32 32 u32 u32 id type name 32 minimum maximum step default_value flags reserved 2 Table 2 struct v412_querymenu u32 u32 us u32 id index name 32 reserved ioctl VIDIOC QUERYCTRL VIDIOC QUERYMENU Identifies the control set by the application See Table 1 1 for predefined IDs Type of control see Table 3 gt Name of the control a NUL terminated ASCII string This information is intended for the user Minimum value inclusive This field is mostly useful to define a lower bound for integer controls Note the value is signed Maximum value inclusive Note the value is signed Generally drivers should not scale hardware control values It may be necessary for example when the name or id imply a particular unit and the hardware actually accepts only multiples of said unit If so drivers must take care values are properly rounded when scaling such that errors will not accumulate on repeated read write cycles This fie
121. d in the VIDIOC QU u32 832 struct v412 queryctrl HH u32 enum v412 ctrl type us L 832 992 IAS92 S32 u32 40132 id value Tli type name 32 minimum maximum step ERYCTRL ioctl for querying controls Whatever x Note signedness default_value flags reserved 2 192 Used in the VIDIOC QU struct v412 querymenu Appendix A Video For Linux Two Header File ERYM 0432 id u32 index u8 name 32 Whatever x 32 reserved Control flags define V4L2 CTRL FLAG DISABLED 0x0001 define V4L2 CTRL FLAG GRABBED 0x0002 Control IDs defined by V4L2 x define V4L2 CID BASE 0x00980900 IDs reserved for driver specific controls define V4L2 CID PRIVATE BASFE 0x08000000 define V4L2 CID BRIGHTNESS VAL2 CID BASE define V4L2 CID CONTRAST VAL2 CID BASE define V4L2 CID SATURATION V4L2_CID_BASE define V4L2_CID_HUE V4L2_CID_BASE define V4L2_CID_AUDIO_VOLUME V4L2_CID_BASE define V4L2_CID_AUDIO_BALANCE V4L2_CID_BASE define V4L2_CID_AUDIO_BASS V4L2_CID_BASE define V4L2_CID_AUDIO_TREBLE V4L2_CID_BASE define V4L2_CID_AUDIO_MUTE V4L2_CID_BASE define V4L2_CID_AUDIO_LOUDNESS V4L2_CID_BASE define V4L2_CID_BLACK_LEVE V4L2_CID_BASE define
122. d no other conditions whatsoever to those of this License You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute However you may accept compensation in exchange for copies If you distribute a large enough number of copies you must also follow the conditions in section 3 You may also lend copies under the same conditions stated above and you may publicly display copies C 4 3 COPYING IN QUANTITY If you publish printed copies of the Document numbering more than 100 and the Document s license notice requires Cover Texts you must enclose the copies in covers that carry clearly and legibly all these Cover Texts Front Cover Texts on the front cover and Back Cover Texts on the back cover Both covers must also clearly and legibly identify you as the publisher of these copies The front cover must present the full title with all words of the title equally prominent and visible You may add other material on the covers in addition Copying with changes limited to the covers as long as they preserve the title of the Document and satisfy these conditions can be treated as verbatim copying in other respects If the required texts for either cover are too voluminous to fit legibly you should put the first ones listed as many as fit reasonably on the actual cover and continue the rest onto adjacent pages If you publish or distribute Opaque copies of the Document numberin
123. d requesting VBI data For details see Section 1 1 Presently no replacement exists for VIDIOCKEY the VAL functions regarding MPEG compression and decompression and microcode programming Drivers may implement the respective V4L ioctls for these purposes 6 2 History of the V4L2 API Soon after the VAL API was added to the kernel it was criticised as too inflexible In August 1998 Bill Dirks proposed a number of improvements and began work on documentation example drivers and applications With the help of other volunteers this eventually became the VAL2 API not just an extension but a replacement for the VAL API However it took another four years and two stable kernel releases until the new API was finally accepted for inclusion into the kernel in its present form 6 2 1 Early Versions 1998 08 20 First version 1998 08 27 select function was introduced 1998 09 10 New video standard interface 1998 09 18 The VIDIOC NONCAP ioctl was replaced by the O TRUNC open flag with synonym O NONCAP O NOIO to indicate a non capturing open The VIDEO STD XXX identifiers are now ordinals rather than bits and video std construct helper function takes id and transmission as arguments 1998 09 28 Revamped video standard Made video controls individually enumerable 1998 10 02 Removed id from video standard renamed color subcarrier fields Renamed VIDIOC QUERYSTD to VIDIOC ENUMSTD and VIDIOC G INPUT to VIDIOC ENUMINPUT Added
124. d this ioctl is merely used to switch the driver into user pointer I O mode To allocate device buffers applications initialize three fields of a v412 requestbuffers structure They set the type field to the respective stream or buffer type the count field to the desired number of buffers and memory must be set to vAL2 MEMORY MMAP When the ioctl is called with a pointer to this structure the driver attempts to allocate the requested number of buffers and stores the actual number allocated in the count field It can be smaller than the number requested even zero when the driver runs out of free memory A larger number is possible when the driver requires more buffers to function correctly When memory mapping I O is not supported the ioctl returns an EINVAL error code Applications can call VIDIOC_REQBUFS again to change the number of buffers however this cannot succeed when any buffers are still mapped A count value of zero frees all buffers after aborting or finishing any DMA in progress an implicit VIDIOC STREAMOFF To negotiate user pointer I O applications initialize only the type field and set memory to VAL2 MEMORY USERPTR When the ioctl is called with a pointer to this structure the driver prepares for user pointer I O when this I O method is not supported the ioctl returns an EINVAL error code 143 Table 1 struct v412_requestbuffers u32 enum v4 2 buf type enum v4 2 memory u32 Return Value On
125. deo VAL2 IN ST NO SYNC VAL2 IN ST NO EQU VAL2 IN ST NO CARRIER VCR and Set Top Box V4L2 IN ST V4L2 IN ST V4L2 IN ST _MACROVISION NO ACCESS VTR Return Value 0x00010000 0x00020000 0x00040000 0x01000000 0x02000000 0x04000000 ioctl VIDIOC ENUMINPUT No synchronization lock No equalizer lock Carrier recovery failed Macrovision is an analog copy prevention system mangling the video signal to confuse video recorders When this flag is set Macrovision has been detected Conditional access denied VTR time constant On success 0 is returned on error 1 and the errno variable is set appropriately EINVAL The struct v412 input index is out of bounds 83 ioctl VIDIOC ENUMOUTPUT Name VIDIOC ENUMOUTPUT Enumerate video outputs Synopsis int ioctl int fd int request struct v412 output argp Arguments fd File descriptor returned by open request VIDIOC ENUMOUTPUT argp Description To query the attributes of a video outputs applications initialize the index field of struct v412 output and call the VIDIOC_ENUMOUTPUT ioctl with a pointer to this structure Drivers fill the rest of the structure or return an EINVAL error code when the index is out of bounds To enumerate all outputs applications shall begin at index zero incrementing by one until the driver returns EINVAL Table 1 struct v4l2 output u32 index Identifies the outpu
126. does not support multiple write streams and the device is already in use EFAULT buf is outside your accessible address space EINTR The call was interrupted by a signal before any data was written EIO I O error This indicates some hardware problem EINVAL The write function is not supported by this driver not on this device or generally not on this type of device 157 Chapter 5 V4L2 Driver Programming to do Chapter 6 History The following chapters document the evolution of the VAL2 API errata or extensions They shall also aid application and driver writers porting their software to later versions of VAL2 6 1 Differences between VAL and V4L2 The Video For Linux API was first introduced in Linux 2 1 to unify and replace various TV and radio device related interfaces developped independently by driver writers in prior years Starting with Linux 2 5 the much improved V4L2 API replaces the VAL API although existing drivers will continue to support V4L in the future either directly or through the V4L2 compatibility layer For a transition period not all drivers will support the V4L2 API 6 1 1 Opening and Closing Devices For compatibility reasons the character device file names recommended for V4L2 video capture overlay radio teletext and raw vbi capture devices did not change from those used by VAL They are listed in Chapter 4 and below in Table 6 1 The V4L videodev module automatically assi
127. driver not one of the VAL2 standard formats b Presumably al V4L2 image formats are defined in Chapter 2 The image format can be selected with the VIDIOC S FMT ioctl 6 1 6 Audio The VIDIOCGAUDIO and VIDIOCSAUDIO ioctl and struct video audio are used to enumerate the audio inputs of a VAL device The equivalent V4L2 ioctls are vIDIOC G AUDIO and VIDIOC S AUDIO using struct v412_audio as discussed in Section 1 5 The audio channel number field counting audio inputs was renamed to index On VIDIOCSAUDIO the mode field selects one of the VIDEO SOUND MONO VIDEO SOUND STEREO VIDEO SOUND LANGI1 or VIDEO SOUND LANG2 audio demodulation modes When the current audio standard is BTSC vibEO SOUND LANG2 refers to SAP and VIDEO SOUND LANGI is meaningless Also undocumented in the VAL specification there is no way to query the selected mode On vIDIOCGAUDIO the driver returns the actually received audio programmes in this field In the VAL2 API this information is stored in the struct v4I2 tuner rxsubchans and audmode fields respectively See Section 1 6 for more information on tuners Related to audio modes struct v4I2 audio also reports if this is a mono or stereo input regardless if the source is a tuner The following fields where replaced by V4L2 controls accessible with the VIDIOC_QUERYCTRL VIDIOC G CTRL and VIDIOC S CTRL ioctls struct video audio V4L2 Control ID
128. e negotiated data format and may change with each buffer for compressed variable size data like JPEG images Drivers must set this field when type refers to an input stream applications when an output stream u32 flags Flags set by the application or driver see Table 3 3 enum v412_ field field Indicates the field order of the image in the buffer see Table 3 8 This field is not used when the buffer contains VBI data Drivers must set it when type refers to an input stream applications when an output stream 42 Chapter 3 Input Output struct timeval timestamp For input streams this is the system time as returned by the gett imeofday function when the first data byte was captured For output streams the data will not be displayed before this time secondary to the nominal frame rate determined by the current video standard in enqueued order Applications can for example zero this field to display frames as soon as possible The driver stores the time at which the first data byte was actually sent out in the timestamp field This permits applications to monitor the drift between the video and system clock struct v412_ timecode imecode When type is V4L2_BUF_TYPE_VIDEO_CAPTURE and the V4L2_BUF_FLAG_TIMECODE flag is set in flags this structure contains a frame timecode In V4L2_FIELD_ALTERNATE mode the top and bottom field contain the same timecode Timecodes are intended to help video editing and are typically
129. e link between video inputs and tuners is now reversed inputs point to the tuner they are on The std substructure became a simple set more about this below and moved into struct v412 input A type field was added Accordingly in struct v412 modulator the output was replaced by an index field In struct v412 frequency the port field was replaced by a tuner field containing the respective tuner or modulator index number A tuner t ype field was added and the reserved field became larger for future extensions satellite tuners in particular 7 The idea of completely transparent video standards was dropped Experience showed that applications must be able to work with video standards beyond presenting the user a menu To this end V4L2 returned to defined standards as v412 std id replacing references to standards throughout the API For details see Section 1 7 VIDIOC_G_STD and viDIOC S STD now take a pointer to this type as argument VIDIOC_QUERYSTD was added to autodetect the received standard In struct v4I2 standard an index field was added for VIDIOC_ENUMSTD A v412_std_id field named id was added as machine readable identifier also replacing the transmission field framerate which is misleading was renamed to frameperiod The 172 10 11 Chapter 6 History now obsolete co1orstandard information originally needed to distguish between variations of standards were removed Struct v412_enumstd ceased to be vIDIOC ENU
130. e of free software license such as the GNU General Public License http www gnu org copyleft gpl html to permit their use in free software 217 Bibliography EIA608 Electronic Industries Alliance http www eia org EIA 608 Recommended Practice for Line 21 Data Service ITU470 International Telecommunication Union http www itu ch ITU R Recommendation BT 470 6 Conventional Television Systems ITU601 International Telecommunication Union http www itu ch ITU R Recommendation BT 601 5 Studio Encoding Parameters of Digital Television for Standard 4 3 and Wide Screen 16 9 Aspect Ratios ITU709 International Telecommunication Union http www itu ch ITU R Recommendation BT 709 5 Parameter values for the HDTV standards for production and international programme exchange JFIF Independent JPEG Group http www ijg org JPEG File Interchange Format Version 1 02 i SMPTE12M Society of Motion Picture and Television Engineers http www smpte org SMPTE 12M 1999 Television Audio and Film Time and Control Code SMPTE170M Society of Motion Picture and Television Engineers http www smpte org SMPTE 170M 1999 Television Composite Analog Video Signal NTSC for Studio Applications SMPTE240M Society of Motion Picture and Television Engineers http www smpte org SMPTE 240M 1999 Television Signal Parameters 1125 Line High Definition Production TELETEXT European
131. e output signal of the graphics card In this case the frame buffer is not modified by the video device and the frame buffer address and pixel format are not needed by the driver The viDIOC S FBUF ioctl is not privileged An application can check for this type of device by calling the VIDIOC_G_FBUF ioctl A driver may support any or none of three clipping methods 1 Chroma keying displays the overlaid image only where pixels in the primary graphics surface assume a certain color 2 A bitmap can be specified where each bit corresponds to a pixel in the overlaid image When the bit is set the corresponding video pixel is displayed otherwise a pixel of the graphics surface 3 A list of clipping rectangles can be specified In these regions ro video is displayed so the graphics surface can be seen here When simultaneous capturing and overlay is supported and the hardware prohibits different image and frame buffer formats the format requested first takes precedence The attempt to capture VIDIOC_S_FMT or overlay VIDIOC S FBUF may fail with an EBUSY error code or return accordingly modified parameters 4 2 4 Overlay Window The overlaid image is determined by cropping and overlay window parameters The former select an area of the video picture to capture the latter how images are overlaid and clipped Cropping initialization at minimum requires to reset the parameters to defaults An example is given in Section 1 10 The ove
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133. e when the index is out of bounds This is a write only ioctl it does not return the current audio output attributes as VIDIOC G AUDOUT does Note connectors on a TV card to loop back the received audio signal to a sound card are not audio outputs in this sense Table 1 struct v412_audioout u32 index Identifies the audio output set by the driver or application 92 ioctl VIDIOC G AUDOUT VIDIOC S AUDOUT u8 name 32 Name of the audio output a NUL terminated ASCII string for example Line Out This information is intended for the user preferably the connector label on the device itself u32 capability Audio capability flags none defined yet Drivers must set this field to zero u32 mode Audio mode none defined yet Drivers and applications on VIDIOC S AUDOUT must set this field to zero u32 reserved 2 Reserved for future extensions Drivers and applications must set the array to zero Return Value On success 0 is returned on error 1 and the errno variable is set appropriately EINVAL No audio outputs combine with the current video output or the number of the selected audio output is out of bounds or it does not combine or there are no audio outputs at all and the ioctl is not supported EBUSY I O is in progress the output cannot be switched 93 ioctl VIDIOC G MPEGCOMP VIDIOC S MPEGCOMP Name VIDIOC G MPEGCOMP VIDIOC S MPEGCOMP Get or set compression parameters Synopsi
134. el Black Level Sync Level Chapter 4 Device Types 60 Chapter 4 Device Types Figure 4 2 ITU R 525 line numbering M NTSC and M PAL 524 525 1 2 3 4 5 6 7 8 9 10 11 12 261 262 1 2 3 4 5 6 7 8 9 10 11 12 e B oy De atti 1st field 262 263 264 265 266 267 268 269 270 271 272 273 274 275 262 263 1 2 3 4 5 6 v4 8 9 10 11 12 LaL 0 P4 nnnnnamTT D 2nd field 61 Chapter 4 Device Types 1 For the purpose of this specification field 2 starts in line 264 and not 263 5 because half line capturing is not supported 62 Figure 4 3 ITU R 625 line numbering 621 308 309 309 622 309 310 310 Chapter 4 Device Types 63 623 624 625 2 3 4 5 6 7 8 22 310 311 312 2 3 4 5 6 7 8 22 1st field 311 312 313 4 315 316 317 318 319 320 321 335 311 312 313 2 3 4 5 6 T 8 22 1 2nd field Chapter 4 Device Types 1 For the purpose of this specification field 2 starts in line 314 and not 313 5 because half line capturing is not supported Remember the VBI image format depends on the selected video standard therefore the application must choose a new standard or query the current standard first Attempts to read or write data ahead of format negotiation or after switching the video standard which may invalidate the negotiated VBI parameters should be refused by the driver A format chan
135. ementing the read or write function or streaming I O must also support the poll function See the po11 manual page for details 152 V4L2 read Name v412 read Read from a V4L2 device Synopsis include lt unistd h gt ssize_t read int fd void buf size t count Arguments fd File descriptor returned by open buf count Description read attempts to read up to count bytes from file descriptor fd into the buffer starting at buf The layout of the data in the buffer is discussed in the respective device interface section see If count is Zero read returns zero and has no other results If count is greater than SSIZE MAX the result is unspecified Regardless of the count value each read call will provide at most one frame two fields worth of data By default read blocks until data becomes available When the oO NONBLOCK flag was given to the open function it returns immediately with an EAGAIN error code when no data is available The select or po11 functions can always be used to suspend execution until data becomes available All drivers supporting the read function must also support select and po11 Drivers can implement read functionality in different ways using a single or multiple buffers and discarding the oldest or newest frames once the internal buffers are filled read never returns a snapshot of a buffer being filled Using a single buffer the driver w
136. ener etr en nen nrete nennen ener nen 109 JPEG Markers Flags iioii a Prep tip tne pepe eec te geo reels 110 str ct y41 modulator 6 d soto oes ote el coe Mr E Et a eat A n 111 vii Fa EPO SSO Ec ON pA PRO RO ico oA d NO Esp Modulator Audio Transmission Flags ceceescceccecssceneeceecesecesceeeeeesaecesceeeeeesaeeeneeeeeeceaeeeneeeees 112 Str ct v4I2 streampatm ore c eet ee deett dere e le to etri don po ote ee ie fo e lebe 116 struct v4D2 captureparm 5 petente diee RR RE re A RE ERE 117 struct v4I2 o tputpatim cases steer termed deese de etim e ite e ee ee EU decus e aveva e teer epe tue 117 Streaming Parameters Capabilites essere enne nennen nennen nen 118 Capture Parameters Flags rie roro cp iae erri ede ee pp eret 118 enum v4 2 prionty cll oe nis vierte ed Pid UH eee leaned 120 struct vAI2 shiced vbi Cap iai Or EEEE EE 122 sliced VBI SetviGess o e eU RE Sinead ieee EE oa PUE DERE ERR 123 StrUCt V412 tUNEL ETER EE AE ATE EEE AE EE ATEEN 125 en ZIP tuner type X EE 126 Tuner and Modulator Capability Flags sese nennen etes 126 Tuner Audio Reception Flags iue tercer bee ee AE E EE 127 Tuner Audio Modes eie HERR a T a a UAR avs EFC HERR 127 Tuner Audio MAtEIX ien eee eere ERO ONES CX E ERR PEN ESTEE CREE THER EE RTI SERERE ERES 128 struct VAI2 capability o egeo eere OP Hd etes 135 Device Capabilities Flags iuret RU queue E qe eie 136 struct
137. entify the driver All V4L2 drivers must support VIDIOC QUERYCAP Applications should always call this ioctl after opening the device 1 3 Application Priority When multiple applications share a device it may be desirable to assign them different priorities Contrary to the traditional rm rf school of thought a video recording application could for example block other applications from changing video controls or switching the current TV channel Another objective is to permit low priority applications working in background which can be Chapter 1 Common API Elements preempted by user controlled applications and automatically regain control of the device at a later time Since these features cannot be implemented entirely in user space V4L2 defines the VIDIOC G PRIORITY and VIDIOC S PRIORITY ioctls to request and query the access priority associate with a file descriptor Opening a device assigns a medium priority compatible with earlier versions of V4L2 and drivers not supporting these ioctls Applications requiring a different priority will usually call VIDIOC_S_PRIORITY after verifying the device with the VIDIOC QUERYCAP ioctl Ioctls changing driver properties such as VIDIOC S INPUT return an EBUSY error code after another application obtained higher priority An event mechanism to notify applications about asynchronous property changes has been proposed but not added yet 1 4 Video Inputs and Outputs Video inputs and
138. equested priority value is invalid or the driver does not support access priorities EBUSY Another application already requested higher priority 121 ioctl VIDIOC G SLICED VBlI CAP Name VIDIOC G SLICED VBI CAP Query sliced VBI capabilities Synopsis int ioctl int fd int request struct v412 sliced vbi cap argp Arguments fd File descriptor returned by open request VIDIOC G SLICED VBI CAP argp Description To find out which data services are supported by a sliced VBI capture or output device applications can call the vVIDIOC G SLICED VBI CAP ioctl It takes a pointer to a struct v412 sliced vbi cap which is filled by the driver Table 1 struct v412 sliced vbi cap ul6 service set A set of all data services supported by the driver Equal to the union ul6 service lines 2 24 Each element of this array contains a set of data services the hardwa Element 525 line systems 625 line systems service lines 0 l 1 1 service lines 0 2323 23 service lines l 164 314 service lines l 23 56 336 The number of VBI lines the hardware can capture or output per frar 122 u32 reserved 4 Table 2 Sliced VBI services ioctl VIDIOC G SLICED VBI CAP Drivers must set service lines 0 0 and service 1ines 1 0 This array is reserved for future extensions Drivers must set it to zer Symbol Value Reference Lines usually Payload V4L2 SLICED TELE
139. er one first in memory Image sizes refer to the frame not fields Images contain both fields the bottom field lines are stored first in memory immediately followed by the top field lines Fields are always stored in temporal order the older one first in memory Image sizes refer to the frame not fields 47 VA4L2 FIELD ALTERNATE 7 Chapter 3 Input Output The two fields of a frame are passed in separate buffers in temporal order i e the older one first To indicate the field parity whether the current field is a top or bottom field the driver or application depending on data direction must set struct v412 buffer field to VAL2 FIELD TOP or V4L2 FIELD BOTTOM Any two successive fields pair to build a frame If fields are successive without any dropped fields between them fields can drop individually can be determined from the struct v412 buffer sequence field Image sizes refer to the frame not fields This format cannot be selected when using the read write I O method Figure 3 1 Field Order Top Field First Transmitted Temporal order top field first transmitted V4L2 FIELD TOP V4AL2 FIELD BOTTOM V4AL2 FIELD ALTERNATE T T ENS EN v4I2 buffer field V4L2 FIELD TOP V4L2 FIELD BOTTOM V4L2 FIELD TOP V4AL2 FIELD INTERLACED V4L2 FIELD SEQ TB V4L2 FIELD BOTTOM V4L2 FIELD TOP V4L2 FIELD BOTTOM 48 Notes Chapter 3 Input Output Fi
140. erate video inputs Synopsis int ioctl int fd int request struct v412 input xargp Arguments fd File descriptor returned by open request VIDIOC ENUMINPUT argp Description To query the attributes of a video input applications initialize the index field of struct v412_input and call the VIDIOC_ENUMINPUT ioctl with a pointer to this structure Drivers fill the rest of the structure or return an EINVAL error code when the index is out of bounds To enumerate all inputs applications shall begin at index zero incrementing by one until the driver returns EINVAL Table 1 struct v4l2 input u32 index Identifies the input set by the application u8 name 32 Name of the video input a NUL terminated ASCII string for example Vin Composite 2 This information is intended for the user preferably the connector label on the device itself u32 type Type of the input see Table 2 gt 1 ioctl VIDIOC ENUMINPUT Video inputs combine with zero or more audio inputs For example one composite video connectors may exist but two audio connectors On the other hand video from a tuner will likely combine only with audio from the same tuner Devices with N audio inputs number them 0 N 1 with N lt 32 Each bit position of audioset represents one audio input For details on audio inputs and how to switch see Section 1 5 Capture devices can have zero or more tuners RF demodulators When the type is set to
141. ercially or noncommercially Secondarily this License preserves for the author and publisher a way to get credit for their work while not being considered responsible for modifications made by others This License is a kind of copyleft which means that derivative works of the document must themselves be free in the same sense It complements the GNU General Public License which is a copyleft license designed for free software We have designed this License in order to use it for manuals for free software because free software needs free documentation a free program should come with manuals providing the same freedoms that the software does But this License is not limited to software manuals it can be used for any textual work regardless of subject matter or whether it is published as a printed book We recommend this License principally for works whose purpose is instruction or reference C 2 1 APPLICABILITY AND DEFINITIONS This License applies to any manual or other work that contains a notice placed by the copyright holder saying it can be distributed under the terms of this License The Document below refers to any such manual or work Any member of the public is a licensee and is addressed as you A Modified Version of the Document means any work containing the Document or a portion of it either copied verbatim or with modifications and or translated into another language A Secondary Section is a named ap
142. ersions of V4L2 VIDIOC_S_FMT and VIDIOC_REQBUFS would permit this to some degree but for simplicity drivers need not support switching the I O method after first switching away from read write other than by closing and reopening the device The following sections describe the various I O methods in more detail 3 1 Read Write Input and output devices support the read and write function respectively when the V4L2_CAP_READWRITE flag in the capabilities field of struct v412_capability returned by the VIDIOC_QUERYCAP ioctl is set Drivers may need the CPU to copy the data but they may also support DMA to or from user memory so this I O method is not necessarily less efficient than other methods merely exchanging buffer pointers It is considered inferior though because no meta information like frame counters or timestamps are passed This information is necessary to recognize frame dropping and to synchronize with other data streams However this is also the simplest I O method requiring little or no setup to exchange data It permits command line stunts like this the vidctrl tool is fictitious gt vidctrl dev video input 0 format YUYV size 352x288 gt dd if dev video of myimage 422 bs 202752 count 1 To read from the device applications use the read function to write the write function Drivers must implement one I O method if they exchange data with applications but it need not be this
143. es x 185 enum v412 bitrate mode VA4L2 BITRATE NONE O0 V4L2 BITRATE CBR VAL2 BITRATE VBR struct v412 bitrate rates ar Appendix A Video For Linux Two Header File not specified constant bitrate x variable bitrate x specified in kbit sec enum v412 bitrate mode mode u32 min u32 target use this one for CBR x u32 max enum v412 mpeg streamtype VAL2 MPEG SS 1 MPEG 1 system stream VAL2 MPEG PS 2 MPEG 2 program stream x VA4L2 MPEG TS 2 MPEG 2 transport stream VA4L2 MPEG PS DVD MPEG 2 program stream with DVD header fixups di enum v412_mpeg_audiotype V4L2_MPEG_AU_2_I x MPEG 2 layer 1 x V4L2 MPEG AU 2 II MPEG 2 layer 2 V4L2 MPEG AU 2 III MPEG 2 layer 3 x V4L2 MPEG AC3 BC3 x V4L2 MPEG LPCM LPCM enum v412 mpeg videotype VAL2 MPEG VI 1 MPEG 1 VAL2 MPEG VI 2 MPEG 2 x enum v412 mpeg aspectratio VAL2 MPEG ASPECT SQUARE 1 square pixel x V4L2 MPEG ASPECT 4 3 2 x 4 3 V4L2_MPEG_ASPECT_16_9 3 fe 16 3 9 V4L2_MPEG_ASPECT_1_221 4 Je d 25 2 struct v412 mpeg compression general enum v412 mpeg streamtype st type struct v412 bitrate transport streams 16 6 L6 6 program stream x ul6 ul6 audio enum v412 m
144. f a struct v4I2 frequency and call the VIDIOC S FREQUENCY ioctl with a pointer to this structure When the requested frequency is not possible the driver assumes the closest possible value However VIDIOC S FREQUENCY is a write only ioctl it does not return the actual new frequency Table 1 struct v4l2 frequency 105 ioctl VIDIOC G FREQUENCY VIDIOC S FREQUENCY u32 tuner The tuner or modulator index number This is the same value as in the struct v412 input tuner field and the struct v412 tuner index field or the struct v4I2 output modulator field and the struct v412_ modulator index field enum v4l2_ tuner type type The tuner type This is the same value as in the struct v412_tuner type field The field is not applicable to modulators i e ignored by drivers u32 frequency Tuning frequency in units of 62 5 kHz or if the struct v412_tuner or struct v412_ modulator capabilities flag VAL2 TUNER CAP LOW is set in units of 62 5 Hz u32 reserved 8 Reserved for future extensions Drivers and applications must set the array to zero Return Value On success 0 is returned on error 1 and the errno variable is set appropriately EINVAL The tuner field is out of bounds 106 ioctl VIDIOC G INPUT VIDIOC S INPUT Name VIDIOC G INPUT VIDIOC S INPUT Query or select the current video input Synopsis int ioctl int fd int request int xargp Arguments fd File descri
145. fied parameters Table 4 1 struct v4l2 window struct v412_ rect w enum v4D field field u32 chromakey struct vAI2 clip clips Size and position of the window relative to the top left corner of the frame buffer defined with VIDIOC S FBUF The window can extend the frame buffer width and height the x and y coordinates can be negative and it can lie completely outside the frame buffer The driver clips the window accordingly or if that is not possible modifies its size and or position Applications set this field to determine which video field shall be overlaid typically one of V4L2 FIELD ANY 0 VAL2 FIELD TOP V4L2 FIELD BOTTOM or V4L2 FIELD INTERLACED Drivers may have to choose a different field order and return the actual setting here When chroma keying has been negotiated with VIDIOC S FBUF applications set this field to the desired host order RGB32 value for the chroma key host order alpha channel When chroma keying has not been negotiated and VIDIOC G FBUF indicated this capability applications can set this field to point to the first in a list of clipping rectangles Like the window coordinates w clipping rectangles are defined relative to the top left corner of the frame buffer Howe u32 clipcount void bitmap When the application set the clips field this field must contain the number of clipping rectangles in the list When clip lists are not supp
146. fract timeperframe ioctl VIDIOC G PARM VIDIOC S8 PARM See Table 4 gt Set by drivers and applications see Table 5 gt This is is the desired period between successive frames output by the driver in seconds The field is intended to repeat frames on the driver side in write mode in streaming mode timestamps can be used u32 extendedmode u32 writebuffers u32 reserved 4 Table 4 Streaming Parameters Capabilites V4L2 CAP TIMEPERFRAME 0x1000 Table 5 Capture Parameters Flags Custom driver specific streaming parameters When unused applications and drivers must set this field to zero Applications using this field should check the driver name and version see Section 1 2 Applications set this field to the desired number of buffers used internally by the driver in write mode Drivers return the actual number of buffers When an application requests zero buffers drivers should just return the current setting rather than the minimum or an error code For details see Section 3 1 Reserved for future extensions Drivers and applications must set the array to zero The frame skipping repeating controlled by the timeperframe field is supported 118 ioctl VIDIOC G PARM VIDIOC S8 PARM V4L2 MODE HIGHQUALITY 0x0001 High quality imaging mode High quality mode is intended for still imaging applications The idea is to get the best possible image quality that the hardware can deliver
147. g and overlay with a single file descriptor for compatibility with V4L and earlier versions of V4L2 4 2 1 Querying Capabilities Devices supporting the video overlay interface set the V4L2_CAP_VIDEO_OVERLAY flag in the capabilities field of struct v412_capability returned by the VIDIOC_QUERYCAP The overlay I O method specified below must be supported Tuners and audio inputs are optional 4 2 2 Supplemental Functions Video overlay devices shall support audio input tuner controls cropping and scaling and streaming parameter ioctls as needed The video input and video standard ioctls must be supported by all video overlay devices 52 Chapter 4 Device Types 4 2 3 Setup Before overlay can commence applications must program the driver with frame buffer parameters namely the address and size of the frame buffer and the image format for example RGB 5 6 5 The VIDIOC G FBUF and VIDIOC S FBUF ioctls are available to get and set these parameters respectively The VIDIOC_S_FBUF ioctl is privileged because it allows to set up DMA into physical memory bypassing the memory protection mechanisms of the kernel Only the superuser can change the frame buffer address and size Users are not supposed to run TV applications as root or with SUID bit set A small helper application with suitable privileges should query the graphics system and program the V4L2 driver at the appropriate time Some devices add the video overlay to th
148. g edge See also Figure 4 1 u32 samples per line u32 sample format Defines the sample format as in Chapter 2 gt a four character code a Usually this is V4L2_PIX_FMT_GREY i e each sample consists of 8 bits with lower values oriented towards the black level Do not assume any other correlation of values with the signal level For example the MSB does not necessarily indicate if the signal is high or low because 128 may not be the mean value of the signal Drivers shall not convert the sample format by software 58 u32 start 2 u32 count 2 Chapter 4 Device Types This is the scanning system line number associated with the first line of the VBI image of the first and the second field respectively See Figure 4 2 gt and Figure 4 3 gt for valid values VBI input drivers can return start values 0 if the hardware cannot reliable identify scanning lines VBI acquisition may not require this information The number of lines in the first and second field image respectively Drivers should be as flexibility as possible For example it may be possible to extend or move the VBI capture window u32 flags u32 reserved 2 Notes Table 4 5 Raw VBI Format Flags V4L2_VBI_UNSYNC 0x0001 V4L2_VBI_INTERLACED 0x0002 See Table 4 5 gt below Currently only drivers set flags applications must set this field to zero This array is reserved for future extensions Drivers and applications m
149. g into account the current video standard cropping and scaling 6 1 3 Video Sources VAL provides the VIDIOCGCHAN and VIDIOCSCHAN ioctl using struct video channel to enumerate the video inputs of a VAL device The equivalent V4L2 ioctls are VIDIOC ENUMINPUT VIDIOC G INPUT and VIDIOC S INPUT using struct v412_input as discussed in Section 1 4 The channe1 field counting inputs was renamed to index the video input types were renamed struct video channel type struct v4l2 input type IVVIDEO TYPE TV VA4L2 INPUT TYPE TUNER IVVIDEO TYPE CAMERA VA4L2 INPUT TYPE CAMERA Unlike the tuners field expressing the number of tuners of this input VAL2 assumes each video input is associated with at most one tuner On the contrary a tuner can have more than one input i e RF connectors and a device can have multiple tuners The index of the tuner associated with the input if any is stored in field tuner of struct v4I2 input Enumeration of tuners is discussed in Section 1 6 The redundant vibEO vc TUNER flag was dropped Video inputs associated with a tuner are of type V4L2 INPUT TYPE TUNER The viDEO VC AUDIO flag was replaced by the audioset field V4L2 considers devices with up to 32 audio inputs Each set bit in the audioset field represents one audio input this video input combines with For information about audio inputs and how to switch see Section 1 5
150. g more than 100 you must either include a machine readable Transparent copy along with each Opaque copy or state in or with each Opaque copy a publicly accessible computer network location containing a complete Transparent copy of the Document free of added material which the general network using public has access to download anonymously at no charge using public standard network protocols If you use the latter option you must take reasonably prudent steps when you begin distribution of Opaque copies in quantity to ensure that this Transparent copy will remain thus accessible at the stated 213 Appendix C GNU Free Documentation License location until at least one year after the last time you distribute an Opaque copy directly or through your agents or retailers of that edition to the public It is requested but not required that you contact the authors of the Document well before redistributing any large number of copies to give them a chance to provide you with an updated version of the Document C 5 4 MODIFICATIONS You may copy and distribute a Modified Version of the Document under the conditions of sections 2 and 3 above provided that you release the Modified Version under precisely this License with the Modified Version filling the role of the Document thus licensing distribution and modification of the Modified Version to whoever possesses a copy of it In addition you must do these things in the Modified Version e
151. ge during active I O is not permitted 4 6 4 Reading and writing VBI images To assure synchronization with the field number and easier implementation the smallest unit of data passed at a time is one frame consisting of two fields of VBI images immediately following in memory The total size of a frame computes as follows count 0 count 1 x samples per line sample size in bytes The sample size is most likely always one byte applications must check the samp1e format field though to function properly with other drivers A VBI device may support read write and or streaming memory mapping or user pointer I O The latter bears the possibility of synchronizing video and VBI data by using buffer timestamps Remember the VIDIOC STREAMON ioctl and the first read write and select call can be resource allocation points returning an EBUSY error code if the required hardware resources are temporarily unavailable for example the device is already in use by another process 4 7 Sliced VBI Data Interface VBI stands for Vertical Blanking Interval a gap in the sequence of lines of an analog video signal During VBI no picture information is transmitted allowing some time while the electron beam of a cathode ray tube TV returns to the top of the screen Sliced VBI devices use hardware to demodulate data transmitted in the VBI V4L2 drivers shall not do this by software see also the raw VBI interface The data is passed as sho
152. ge format structure struct v412_format becomes struct v412_pix_format These ioctls become obsolete VIDIOC S INFMT VIDIOC G INFMT VIDIOC S OUTFMT VIDIOC G OUTFMT VIDIOC S VBIFMT VIDIOC G VBIFMT Similar to item 2 VIDIOC G S PARM and VIDIOC G S OUTPARM are merged along with the corresponding get functions A type field will indicate which stream the parameters are for set to a VAL2 BUF TYPE value struct v412 streamparm 2 32 type union struct v412 captureparm capture struct v412 outputparm output u8 raw data 200 parm These ioctls become obsolete VIDIOC_G_OUTPARM VIDIOC S OUTPARM The way controls are enumerated is simplified Simultaneously two new control flags are introduced and the existing flag is dropped Also the catname field is dropped in favor of a group name To enumerate controls call VIDIOC QUERYCTRL with successive id s starting from VAL2 CID BASE or V4L2 CID PRIVATE BASE and stop when the driver returns the EINVAL error code Controls that are not supported on the hardware are marked with the VAL2 CTRL FLAG DISABLED flag Additionally controls that are temporarily unavailable or that can only be controlled from another file descriptor are marked with the VAL2 CTRL FLAG GRABBED flag Usually a control that is GRABBED but not DISABLED can be read but changed The group name indicates a possibly narrower classification than the category In other words there may be 169
153. general purpose data format negotiation ioctls vIDIOC G FMT and VIDIOC S FMT They take a pointer to a struct v412 format as argument here the struct v412 window named win of its fmt union is used The x y width and height fields of struct video window moved into struct v412_rect substructure w of struct v412 window The chromakey clips and clipcount fields remained unchanged Struct video clip was renamed to struct v412 clip also containing a struct v412 rect but the semantics are still the same The VIDEO WINDOW INTERLACE flag was dropped instead applications must set the field field to V4L2 FIELD ANY or V4L2 FIELD INTERLACED The VIDEO WINDOW CHROMAKEY flag moved into struct v412 framebuffer renamed to V4L2 FBUF FLAG CHROMAKEY In VAL storing a bitmap pointer in clips and setting clipcount to VIDEO CLIP BITMAP 1 requests bitmap clipping using a fixed size bitmap of 1024 x 625 bits Struct v4I2 window has a separate bitmap pointer field for this purpose and the bitmap size is determined by w width and w height The VIDIOCCAPTURE ioctl to enable or disable overlay was renamed to VIDIOC OVERLAY 6 1 8 Cropping To capture only a subsection of the full picture VAL provides the VIDIOCGCAPTURE and VIDIOCSCAPTURE ioctl using struct video capture The equivalent V4L2 ioctls are VIDIOC G CROP and VIDIOC S CROP using struct v412 crop and the related VIDIOC_CROPCAP ioctl T
154. ges eee 170 6 2 7 V4L2 Version 0 20 2000 11 23 cssssssseseseeseeeeeeeneee nennen nennen eren 171 6 2 8 VAL2 Version 0 20 2002 07 25 csset nennen nee 171 6 2 9 VAL2 in Linux 2 5 46 2002 10 enne nnne 171 6 2 10 V4L2 2003 06 19 5 rsen deeem pera ER RETE EP eben 175 6 2 11 V41 2 2003 1 1205 iiec eet ER ette rer tereti tet tt b tre ret eet ise pied 175 6 2 12 V4L2 in Linux 2 6 6 2004 05 09 oo ccccssecesccesscessecssceseeceseeesseeeecsseeessensees 176 62 13 VAL m Tn0x 2 06 84 Laici ec aede eere eite pee dete deeds 176 6 2 14 V4L2 spec erratum 2004 08 01 sese 176 6 2 15 V4L2 in Linux 2 6 14 enne nennt nnne n eene trennen enne 176 6 2 16 VALE 2n Linux 2 6 15 iei er REEF ortu 177 6 2 17 V4L2 spec erratum 2005 11 27 nennen eene ee 177 6 2 18 V4L2 spec erratum 2006 01 10 eene 177 6 2 19 V4L2 spec erratum 2006 02 03 eene nennen nennen nen 177 6 3 Relation of V4L2 to other Linux multimedia APIs eese 177 6 3 1 X Video Extens10n 5 nep ed Eee ee ERI BEERUHONS 6 3 2 Digital Vid o ons ect e rt he eis E Gre tt iet tee ded 6 3 3 Audio Interfaces e ente PEORES TA eS A Video For Linux Two Header File ssscscssssssssssscsccscssssssccsessscsseesecssscsssssssessessseeseeseeees B Video Capture Example eeeeeteeeon teret or thi ra tato tb ton ain res nota bti eu Peta so lepus rii een at eaten d ett oa C GNU Free D
155. ght minwidth minheight maxframerate were removed this information is available as described in Section 1 9 and Section 1 7 V4AL2 FLAG SELECT was removed this function is considered important enough that all V4L2 drivers exchanging data with applications must support select The redundant flag V4L2 FLAG MONOCHROME was removed this information is available as described in Section 1 9 4 In struct v412 input the ssoc audio field and the capability field and its only flag VAL2 INPUT CAP AUDIO was replaced by the new audioset field Instead of linking one video input to one audio input this field reports all audio inputs this video input combines with New fields are tuner reversing the former link from tuners to video inputs std and status Accordingly struct v412 output lost its capability and assoc audio fields audioset modulator and std where added 5 The struct v412 audio field audio was renamed to index consistent with other structures Capability flag V4L2_AUDCAP_STEREO was added to indicated if this is a stereo input V4L2_AUDCAP_EFFECTS and the corresponding v4L2_AUDMODE flags where removed this can be easily implemented using controls However the same applies to AVL which is still there The struct v412 audioout field audio was renamed to index 6 The struct v4I2 tuner input field was replaced by an index field permitting devices with multiple tuners Th
156. gnal With this interface applications can control the encoding process and move images from user space to the driver Conventionally V4L2 video output devices are accessed through character device special files named dev vout and dev vout0 to dev voutN No minor numbers were recommended yet dev vout is typically a symbolic link to the preferred video output device 4 3 1 Querying Capabilities Devices supporting the video output interface set the V4L2_CAP_VIDEO_OUTPUT flag in the capabilities field of struct v412 capability returned by the VIDIOC_QUERYCAP As secondary device functions they may also support the raw VBI output v4L2_CAP_VBI_OUTPUT interface At least one of the read write or streaming I O methods must be supported Modulators and audio outputs are optional 4 3 2 Supplemental Functions Video output devices shall support audio output modulator controls cropping and scaling and streaming parameter ioctls as needed The video output and video standard ioctls must be supported by all video output devices 55 Chapter 4 Device Types 4 3 3 Image Format Negotiation The output is determined by cropping and image format parameters The former select an area of the video picture where the image will appear the latter how images are stored in memory i e in RGB or YUV format the number of bits per pixel or width and height Together they also define how images are scaled in the process As usual these parame
157. gned int cmd unsigned long arg int func struct inode inode struct file file unsigned int cmd void xarg helper functions to alloc release struct video device th later can be used for video device release x struct video device xvideo device alloc void void video device release struct video device vfd endif MISCELLANEOUS Four character code FOURCC x define v412 fourcc a b c d N C 032 a lt lt 0 __u32 5 lt lt 8 __u32 C lt lt 16 C 032 a lt lt 24 ENUMS enum v412 field V4L2 FIELD ANY 0 driver can choose from none top bottom interlaced depending on whatever it thinks is approximate x VAL2 FIELD NONE 1 this device has no fields VAL2 FIELD TOP 2 top field only V4L2 FIELD BOTTOM 3 bottom field only V4L2 FIELD INTERLACED 4 both fields interlaced x VA4L2 FIELD SEQ TB 5 both fields sequential into one buffer top bottom order x VAL2 FIELD SEQ B 6 same as above bottom top order x VAL2 FIELD ALTERNATE 7 both fields alternating into separate buffers define V4L2_FIELD_HAS_TOP field N field VA4L2 FIELD TOP N field VA4L2 FIELD INTERLACED V field VA4L2
158. gns minor numbers to drivers in load order depending on the registered device type We recommend V4L2 drivers by default register devices with the same numbers but in principle the system administrator can assign arbitrary minor numbers using driver module options The major device number remains 81 Table 6 1 V4L Device Types Names and Numbers Device Type File Name Minor Numbers Video capture and overlay dev video and dev bttv0a 0 63 dev videoO to dev video63 Radio receiver dev radioe dev radioO to 64 127 dev radio63 Teletext decoder dev vtx dev vtx0 to 192 223 dev vtx31 Raw VBI capture dev vbi dev vbi0 to 224 2390 dev vbil5 Notes a According to Documentation devices txt these should be symbolic links to dev videoO Note the origina VAL prohibits or used to multiple opens VAL2 drivers may support multiple opens see Section 1 1 for details and consequences VAL drivers respond to V4L2 ioctls with the EINVAL error code The V4L2 videodev module backward compatibility layer can translate V4L ioctl requests to their V4L2 counterpart however a VAL2 driver usually needs more preparation to become fully VAL compatible This is covered in more detail in Chapter 5 gt 159 6 1 2 Querying Capabilities The VAL vIDIOCGCAP ioctl is equivalent to V4L2 s VIDIOC QUI Chapter 6 History ERYCAP The name field in struct video capability became card in struct v412 capab
159. gure 3 2 Field Order Bottom Field First Transmitted Temporal order bottom field first transmitted V4L2 FIELD TOP V4AL2 FIELD BOTTOM VAL2 FIELD ALTERNATE _ T T ENS ee EN v4I2 buffer field V4L2 FIELD BOTTOM V4L2 FIELD TOP V4L2 FIELD BOTTOM V4l2 FIELD TOP V4L2 FIELD BOTTOM V4L2_FIELD_TOP V4AL2 FIELD INTERLACED V4L2 FIELD SEQ BT It would be desirable if applications could depend on drivers supporting all I O interfaces but as much as the complex memory mapping I O can be inadequate for some devices we have no reason to require this interface which is most useful for simple applications capturing still images At the driver level select and po11 are the same and select is too important to be optional One could use one file descriptor and set the buffer type field accordingly when calling VIDIOC_QBUF etc but it makes the select function ambiguous We also like the clean approach of one file descriptor per logical stream Video overlay for example is also a logical stream although the CPU is not needed for continuous operation Random enqueue order permits applications processing images out of order such as video codecs to return buffers earlier reducing the probability of data loss Random fill order allows drivers to reuse buffers on a LIFO basis taking advantage of caches holding scatter gather lists and the like At the driver level select and po11 are the same and select is too imp
160. h minor number 64 and 65 base 64 Chapter 1 Common API Elements When no minor number is given as module option the driver supplies a default Chapter 4 gt recommends the base minor numbers to be used for the various device types Obviously minor numbers must be unique When the number is already in use the offending device will not be registered By convention system administrators create various character device special files with these major and minor numbers in the dev directory The names recomended for the different V4L2 device types are listed in Chapter 4 gt The creation of character special files with mknod is a privileged operation and devices cannot be opened by major and minor number That means applications cannot reliable scan for loaded or installed drivers The user must enter a device name or the application can try the conventional device names Under the device filesystem devfs the minor number options are ignored V4L2 drivers or by proxy the videodev module automatically create the required device files in the dev v41 directory using the conventional device names above 1 1 2 Related Devices Devices can support several related functions For example video capturing video overlay and VBI capturing are related because these functions share amongst other the same video input and tuner frequency V4L and earlier versions of V4L2 used the same device name and minor number for video capturing and overlay bu
161. has as many pad bytes after its rows Example 2 1 v4L2_PIX_FMT_NV12 4 x 4 pixel image Byte Order Each cell is one byte start 0 Y 00 Y oi Y o Y os start 4 Y io Yu Yr Y 13 start 8 Y o Y Y 2 Y start 12 Y 30 Y s Y Y ss start 4 16 Cboo Croo Cbo Croi start 4 20 Cbio Crio Cbi Cri Color Sample Location 0 1 2 0 Y C C 1 Y Y Y 2 Y Y Y C C 3 Y Y Y 35 2 5 Compressed Formats Chapter 2 Image Formats to do see also VIDIOC_G_MPEGCOMP VIDIOC S MPEGCOMP VIDIOC G JPEGCOMP VIDIOC S JPEGCOMP The only compressed standard format should be M JPEG 2 6 Reserved Format Identifiers These formats are not defined by this specification they are just listed for reference and to avoid naming conflicts If you want to register your own format send an e mail to the VAL mailing list https listman redhat com mailman listinfo video4linux list for inclusion in the videodev h file If you want to share your format with other developers add a link to your documentation and send a copy to the maintainer of this document Michael Schimek lt mschimek gmx at gt for inclusion in this section If you think your format should be listed in a standard format section please make a proposal on the VAL mailing list Table 2 4 Reserved Image Formats Identifier Code Details VAL2 PIX FMT YYUV YYUV unknown VAL2 PIX FMT HI240 HD4 Used by the BTTV driver http bytesex
162. he hardware can scale images The IVAL2 API implies the scale factor by setting the cropping dimensions and image size with he VIDIOC S CROP and VIDIOC S FMT ioctl respectively The driver returns the closest sizes possible For more information on cropping and scaling see Section 1 10 IVID TYPE MONOCHROMI Fl Applications can enumerate the supported image formats with the IVIDIOC ENUM FMT ioctl to determine if the device supports erey scale capturing only For more information on image formats see Chapter 2 gt 160 Chapter 6 History struct video capability type struct v4l2 capability Purpose capabilities flags IVID TYPE SUBCAPTURI Ei Applications can call the VIDIOC G CROP ioctl to determine if the device supports capturing a subsection of the full picture cropping in V4L2 If not the ioctl returns the EINVAL error code For more information lon cropping and scaling see Section 1 10 gt The audios field was replaced by capabilities flag V4AL2 CAP AUDIO indicating if the device has any audio inputs or outputs To determine their number applications can enumerate audio inputs with the VIDIOC G AUDIO ioctl The audio ioctls are described in Section 1 5 The maxwidth maxheight minwidth and minheight fields were removed Calling the VIDIOC S FMT or VIDIOC TRY FMT ioctl with the desired dimensions returns the closest size possible takin
163. he driver shall fall back to mono or stereo mode Only UNER ANALOG TV tuners support this V4L2 mode Note the V4L2 TUN VAL2 ER MODE LANG2 and UNER MODE SAP are synonyms Selected var2 TUNER MODE Received MONO STEREO LANG1 LANG2 SAP VAL2 TUNER SUB ONO Mono Mono Mono Mono Mono ONO SAP Mono Mono Mono Mono SAP STEREO L R L R Stereo L R Stereo L R preferred or Mono preferred or Mono L R L R STEREO SAP L R L R Stereo L R SAP preferred or Mono L R LANG1 LANG2 Language 1 Langl Lang2 Language 1 Language 2 preferred or Langl Langl Return Value On success 0 is returned on error 1 and the errno variable is set appropriately EINVAL The struct v412 tuner index is out of bounds 128 ioctl VIDIOC LOG STATUS Name VIDIOC LOG STATUS Log driver status information Synopsis int ioctl int fd int request Description As the video audio devices become more complicated it becomes harder to debug problems When this ioctl is called the driver will output the current device status to the kernel log This is particular useful when dealing with problems like no sound no video and incorrectly tuned channels Also many modern devices autodetect video and audio standards and this ioctl will report what the device thinks what the standard is Mismatches may give an indication where the problem is This i
164. he image into visible graphics memory as opposed to merely displaying the image in place of the original display contents The frame buffer is an overlay surface the same size as the capture Use chromakey when VA4L2 FBUF CAP CHROMAKEY indicates this capability The other clipping methods are negotiated with the viDIOC S FMT ioctl see also Section 4 2 On success 0 is returned on error 1 and the errno variable is set appropriately EACCES VIDIOC S FBUF can only be called by a privileged user EBUSY The frame buffer parameters cannot be changed at this time because overlay is already enabled or capturing is enabled and the hardware cannot capture and overlay simultaneously EINVAL The ioctl is not supported or the vVIDIOC S FBUF parameters are unsuitable 101 ioctl VIDIOC G FMT VIDIOC S FMT VIDIOC TRY FMT Name VIDIOC G FMT VIDIOC S FMT VIDIOC TRY FMT Get or set the data format try a format Synopsis int ioctl int fd int request struct v412 format xargp Arguments fd File descriptor returned by open request VIDIOC_G_FMT VIDIOC_S_FMT VIDIOC_TRY_FMT argp Description These ioctls are used to negotiate the format of data typically image format exchanged between driver and application To query the current parameters applications set the type field of a struct v412_ format to the respective buffer stream type For example video capture devices use V4L2 BUF T
165. hen VIDIOC_QBUF is called with a pointer to this structure the driver sets the V4L2_BUF_FLAG_QUEUED flag and clears the v4AL2 BUF FLAG MAPPED and VAL2 BUF FLAG DONE flags in the flags field or it returns an error code This ioctl locks the memory pages of the buffer in physical memory they 131 ioctl VIDIOC QBUF VIDIOC DQBUF cannot be swapped out to disk Buffers remain locked until dequeued until the vIDIOC STREAMOFF or VIDIOC REQBUFS ioctl are called or until the device is closed Applications call the VIDIOC_DQBUF ioctl to dequeue a filled capturing or displayed output buffer from the driver s outgoing queue They just set the type and memory fields of a struct v412_buffer as above when vIDIOC DOBUF is called with a pointer to this structure the driver fills the remaining fields or returns an error code By default VIDIOC_DQBUF blocks when no buffer is in the outgoing queue When the O NONBLOCK flag was given to the open function VIDIOC DOBUF returns immediately with an EAGAIN error code when no buffer is available The v412 buffer structure is specified in Section 3 5 Return Value On success 0 is returned on error 1 and the errno variable is set appropriately EAGAIN Non blocking I O has been selected using O_NONBLOCK and no buffer was in the outgoing queue EINVAL The buffer t ype is not supported or the index is out of bounds or no buffers have been allocated yet or the use
166. his is a rather complex matter see Section 1 10 for details The x y width and height fields moved into struct v412 rect substructure c of struct v412 crop The decimation field was dropped The scaling factor is implied by the size of the cropping rectangle and the size of the captured or overlaid image The VIDEO CAPTURE ODD and VIDEO CAPTURE EVEN flags to capture only the odd or even field respectively were replaced by v4L2 FIELD TOP and V4L2 FIELD BOTTOM in the field named 164 field of struct v412 pix format and struct v412_ the capture or overlay format with the VIDIOC S Chapter 6 History window These structures are used to determine FMT ioctl 6 1 9 Reading Images Memory Mapping 6 1 9 1 Capturing using the read m There is no essential difference between reading im read function Supporting this method is optio available can be determined with the VIDIOC_QUI ethod ages from a V4L or V4L2 device using the nal for VAL2 devices Whether the function is ERYCAP ioctl All VAL2 devices exchanging data with applications must support the select and po11 function To select an image format and size VAL provides the VIDIOCSPICT and VIDIOCSWIN ioctls VAL2 uses the general purpose data format negotiation ioctls vVIDIOC G FMT and VIDIOC S FMT They take a pointer to a struct v412 format as argument fmt union is used here the struct v412 pix form
167. ices supporting it RDS data can be read with the read function The data is packed in groups of three as follows 1 First Octet Least Significant Byte of RDS Block 2 Second Octet Most Significant Byte of RDS Block 3 Third Octet Bit 7 Error bit Indicates that an uncorrectable error occurred during reception of this block Bit 6 Corrected bit Indicates that an error was corrected for this data block Bits 5 3 Received Offset Indicates the offset received by the sync system Bits 2 0 Offset Name Indicates the offset applied to this data It was argued the RDS API should be extended before integration into V4L2 no new API has been devised yet Please write to the Video4Linux mailing list for discussion https listman redhat com mailman listinfo video4linux list Meanwhile no V4L2 driver should set the V4L2_CAP_RDS_CAPTURE capability flag 1 A common application of two file descriptors is the XFree86 Xv V4L interface driver and a VAL2 application While the X server controls video overlay the application can take advantage of memory mapping and DMA In the opinion of the designers of this API no driver writer taking the efforts to support simultaneous capturing and overlay will restrict this ability by requiring a single file descriptor as in V4L and earlier versions of VAL2 Making this optional means applications depending on two file descriptors need backup routines to be compatible with all drivers which is considerable mo
168. ile Ve T wD x Er O IMAGE FORMAT struct v412 pix format u32 width EE C height u32 pixelformat enum v412 field field u32 bytesperline x for padding zero if unused x u32 Sizeimage enum v412 colorspace colorspace u32 priv private data depends on pixelformat Pixel format FOURCC depth Description define VA4L2 PIX FMT RGB332 v412 fourcc R G B 1 8 RGB 3 3 2 x define V4L2_PIX_FMT_RGB555 v412 fourcc R G B O 16 RGB 5 5 5 define VA4AL2 PIX FMT RGB565 v412 fourcCc R G B P 16 RGB 5 6 5 define VA4L2 PIX FMT RGB555X v412 fourcc R G B Q 16 RGB 5 5 5 BE x define VA4AL2 PIX FMT RGB565X v412 fourcCcC R G B R x 16 RGB 5 6 5 BE x define VA4L2 PIX FMT BGR24 v412 fourcc B G R 3 x 24 BGR 8 8 8 x define V4L2 PIX FMT RGB24 v412 fourcc R G B 3 24 RGB 8 8 8 define V4L2 PIX FMT BGR32 v412 fourcc B G R 4 x 32 BGR 8 8 8 8 x define V4L2 PIX FMT RGB32 v412 fourcc R G B 4 32 RGB 8 8 8 8 define VA4L2 PIX FMT GREY v412 fourcc G R E Y x 8 Greyscale define V4L2 PIX FMT YVU410 v412 fourcc Y V U 9 x 9 YVU 4 1 0 x define VA4L2 PIX FMT YVU420 v412 fourcc Y V 1 2 x 12 YVU 4 2 0 x define VA4L2 PIX FMT YUYV 412 fourco Yny Urp A a NJ fe 16 YXUV 4 2 22 x define VA4L2 PIX FMT UYVY v4l2 fource Ut tx tt UN Pe 16 XUV 4 21 72 x defi
169. ility type was replaced by capabilities Note V4L2 does not distinguish between device types like this better think of basic video input video output and radio devices supporting a set of related functions like video capturing video overlay and VBI capturing See Section 1 1 for an introduction struct video capability type struct v4l2 capability capabilities flags Purpose field capability of struct v412_framebuffer VID TYPE CAPTURE V4L2 CAP VIDEO CAPTURE The video capture interface is supported VID TYPE TUNER VA4L2 CAP TUNER The device has a tuner or modulator VID TYPE TELETEXT VA4L2 CAP VBI CAPTURE The raw VBI capture interface is supported VID TYPE OVERLAY VAL2 CAP VIDEO OVERLAY The video overlay interface is supported VID TYPE CHROMAKEY VAL2 FBUF CAP CHROMAKEY inWhether chromakey overlay is supported For more information on overlay see Section 4 2 IVID TYPE CLIPPING V4L2 FBUF CAP LIST CLIPPI and V4L2 FBUF CAP BITMAP CLIP in field capability of struct v412 framebuffer Whether clipping the overlaid image is supported see Section wb xc VID TYPE FRAMERAM VAL2 FBUF CAP EXTERNOVERIMMhether overlay overwrites not set in field capability of Iframe buffer memory see struct v412_framebuffer Section 4 2 VID TYPE SCALES This flag indicates if t
170. ill stop capturing when the application starts reading the buffer until the read is finished Thus only the period of the vertical blanking interval is available for reading or the capture rate must fall below the nominal frame rate of the video standard The behavior of read when called during the active picture period or the vertical blanking separating the top and bottom field depends on the discarding policy A driver discarding the oldest frames keeps capturing into an internal buffer continuously overwriting the previously not read frame and returns the frame being received at the time of the read call as soon as it is complete 153 V4L2 read A driver discarding the newest frames stops capturing until the next read call The frame being received at read time is discarded returning the following frame instead Again this implies a reduction of the capture rate to one half or less of the nominal frame rate An example of this model is the video read mode of the bttv driver initiating a DMA to user memory when read is called and returning when the DMA finished In the multiple buffer model drivers maintain a ring of internal buffers automatically advancing to the next free buffer This allows continuous capturing when the application can empty the buffers fast enough Again the behavior when the driver runs out of free buffers depends on the discarding policy Applications can get and set the number of buffers used
171. ine V4L2 STD PAL N v412 std id 0x00000200 define VA4L2 STD PAL NC v412 std id 0x00000400 define V4L2 STD PAL 60 v412 std id 0x00000800 V4L2 STD PAL 60 is a hybrid standard with 525 lines 60 Hz refresh rate and PAL color modulation with a 4 43 MHz color subcarrier Some PAL video recorders can play back NTSC tapes in this mode for display on a 50 60 Hz agnostic PAL TV define V4L2 STD NTSC M v412 std id 0x00001000 define V4L2 STD NTSC M JP v412 std id 0x00002000 define V4L2 STD NTSC 443 v412 std id 0x00004000 V4L2 STD NTSC 443 is a hybrid standard with 525 lines 60 Hz refresh rate and NTSC color modulation with a 4 43 MHz color subcarrier 87 V4L2 STD ATSC 8 VSB and V4L2 STD ATSC 16 VSB are U S terrestrial digital TV standards Presently the VAL2 API does not support digital TV See also the Linux DVB API at define V4L2 STD SECAM B define V4L2 STD SECAM D define V4L2 STD SECAM G define V4L2 STD SECAM H define V4L2 STD SECAM K define V4L2 STD SECAM K1 define V4L2 STD SECAM define V4L2 STD SECAM LC ATSC HDTV x define V4L2 STD ATSC 8 VSB define V4L2 STD ATSC 16 VSB http linuxtv org define define define define define define define define define define v4 v4 v4 v4 v4 v4 L2 S L2 S ID PAL BG ID PAL DK L2 S1 L2 S ID PAL ID NTSC
172. ines Both applications and drivers can set this field to request padding bytes at the end of each line Drivers however may ig u32 sizeimage enum v4l2 colorspaeelorspace u32 priv Notes Applications must initialize this field Together with base it defines the frame buffer memory accessible by the driver The field is not used when the driver sets VAL2 FBUF CAP EXTERNOVERLAY This information supplements the pixelformat and must be set by the driver see Section 2 2 Reserved for additional information about custom driver defined formats When not used drivers and applications must set this field to zero 100 Table 2 Frame Buffer Capability Flags VAL2 FBUF CAP EXTERNOVERLAY 0x0001 VAL2 FBUF CAP CHROMAKEY 0x0002 VAL2 FBUF CAP LIST CLIPPING 0x0004 VA4L2 FBUF CAP BITMAP CLIPPINQx0O08 Table 3 Frame Buffer Flags VAL2 FBUF FLAG PRIMARY 0x0001 VA4L2 FBUF FLAG OVERLAY 0x0002 VA4L2 FBUF FLAG CHROMAKEY 0x0004 Return Value ioctl VIDIOC_G_FBUF VIDIOC S8 FBUF The video is overlaid externally onto the video signal of the graphics card The device supports clipping by chroma keying the image into the display The device supports clipping using a list of clip rectangles The device supports clipping using a bit mask The frame buffer is the primary graphics surface In other words the overlay is destructive the video hardware will write t
173. influenced by APP ONLY not by this pr App segment i EG APPn segment Unless you exactly know wha align op t align align t to be written EG APPn segment x EG COM segment segment x go into the JPI hem untouched S will make the but there will which can read it of the APP and COM marker len and COM len operty Define Huffman Tables Define Quantization Tables x Define Restart Interval x Comment segment driver will x allways use APPO BU EE ti 187 struct v412 requestbuffers u32 enum v412 buf type enum v412 memory u32 struct v412 buffer Appendix A Video For Linux Two Header File count type memory reserved 2 u32 index enum v412 buf type type u32 bytesused u32 flags enum v412 field field struct timeval timestamp struct v412 timecode timecode u32 sequence memory location x enum v412 memory memory union 032 offset unsigned long userptr m u32 length u32 input u32 reserved i Flags for flags field x define V4L2_BUF_FLAG_MAPPED 0x0001 Buffer is mapped flag define V4L2_BUF_FLAG_QUEUE 0x0002 x Buffer is queued for processing define V4L2 BUF FLAG DONE 0x0004 x Buffer is ready x define VA4L2 BUF FLAG KEYFRAME 0x
174. information is transmitted allowing some time while the electron beam of a cathode ray tube TV returns to the top of the screen Using an oscilloscope you will find here the vertical synchronization pulses and short data packages ASK modulated onto the video signal These are transmissions of services such as Teletext or Closed Caption Subject of this interface type is raw VBI data as sampled off a video signal or to be added to a signal for output The data format is similar to uncompressed video images a number of lines times a number of samples per line we call this a VBI image Conventionally V4L2 VBI devices are accessed through character device special files named dev vbi and dev vbi0 to dev vbi15 with major number 81 and minor numbers 224 to 239 dev vbi is typically a symbolic link to the preferred VBI device This convention applies to both input and output devices To address the problems of finding related video and VBI devices VBI capturing is also available as device function under dev video VBI output under dev vout To capture raw VBI data from these devices applications must call the VIDIOC_S_FMT ioctl Accessed as dev vbi raw VBI capturing or output is the default device function 4 6 1 Querying Capabilities Devices supporting the raw VBI capturing or output API set the V4AL2 CAP VBI CAPTURE or VAL2 CAP VBI OUTPUT flags respectively in the capabilities field of struct v412 capability returned by the VIDIOC_Q
175. ing the VIDIOC_REQBUF S with the desired buffer type No buffers are allocated beforehands consequently they are not indexed and cannot be queried like mapped buffers with the VIDIOC_QUERYBUF ioctl Example 3 2 Initiating streaming I O with user pointers struct v412 requestbuffers reqbuf memset amp reqbuf 0 sizeof reqbuf reqbuf type V4L2_BUF_TYPE_VIDEO_CAPTURE reqbuf memory V4L2_MEMORY_USERPTR EM if ioctl fd VIDIOC REOBUFS amp reqbuf 1 if errno EINVAL printf Video capturing or user pointer streaming is not supported n else perror VIDIOC_REQBUFS exit EXIT_FAILURE Buffer addresses and sizes are passed on the fly with the VIDIOC_QBUF ioctl Although buffers are commonly cycled applications can pass different addresses and sizes at each VIDIOC_QBUF call If 40 Chapter 3 Input Output required by the hardware the driver swaps memory pages within physical memory to create a continuous area of memory This happens transparently to the application in the virtual memory subsystem of the kernel When buffer pages have been swapped out to disk they are brought back and finally locked in physical memory for DMA Filled or displayed buffers are dequeued with the vibroc poBur ioctl The driver can unlock the memory pages at any time between the completion of the DMA and this ioctl The memory is also unlocked when VIDIOC_STREAMOFF is called
176. internally by the driver with the streaming parameter ioctls see streaming par They are optional however The discarding policy is not reported and cannot be changed For minimum requirements see the respective device interface section in Return Value On success the number of bytes read is returned It is not an error if this number is smaller than the number of bytes requested or the amount of data required for one frame This may happen for example because read was interrupted by a signal On error 1 is returned and the errno variable is set appropriately In this case the next read will start at the beginning of a new frame Possible error codes are EAGAIN Non blocking I O has been selected using O NONBLOCK and no data was immediately available for reading EBADF dis not a valid file descriptor or is not open for reading or the process already has the maximum number of files open EBUSY The driver does not support multiple read streams and the device is already in use EFAULT buf is outside your accessible address space EINTR The call was interrupted by a signal before any data was read EIO I O error This indicates some hardware problem or a failure to communicate with a remote device USB camera etc EINVAL The read function is not supported by this driver not on this device or generally not on this type of device 154 V4L2 select Name v412 select Synchronous I O mu
177. ision would only transmit brightness information To add color in a way compatible with existing receivers a new signal carrier was added to transmit the color difference signals Secondary in the YUV format the U and V components usually have lower resolution than the Y component This is an analog video compression technique taking advantage of a property of the human visual system being more sensitive to brightness information VAL2 PIX FMT GREY GREY Name V4L2 PIX FMT GREY Grey scale image Description This is a grey scale image It is really a degenerate Y CbCr format which simply contains no Cb or Cr data Example 2 1 VAL2 PIX FMT GREY 4 x 4 pixel image Byte Order Each cell is one byte start 4 0 Y oo Y oi Y o Y os start 4 Y 10 Yu Yr Y 13 start 8 Y o Y n Y Y start 4 12 Y 30 Y s Y Y ss 27 V4L2 PIX FMT YUYV YUYV Name VAL2 PIX FMT YUYV Packed format with 2 horizontal chroma resolution also known as YUV 4 2 2 Description In this format each four bytes is two pixels Each four bytes is two Y s a Cb and a Cr Each Y goes to one of the pixels and the Cb and Cr belong to both pixels As you can see the Cr and Cb components have half the horizontal resolution of the Y component v4AL2 PIX FMT YUYV is known in the Windows environment as YUY2 Example 2 1 vAL2 PIX FMT YUYV 4 x 4 pixel image Byte Order Each cell is one byte start 4 0 Y oo start 8
178. itable property the audio mode To select the current audio input and change the audio mode applications initialize the index and mode fields and the reserved array of a v412 audio structure and call the VIDIOC_S_AUDIO ioctl Drivers may switch to a different audio mode if the request cannot be satisfied However this is a write only ioctl it does not return the actual new audio mode 90 Table 1 struct v412_audio u32 u8 u32 u32 u32 index name 32 capability mode reserved 2 Table 2 Audio Capability Flags V4L2_AUDCAP_STE RE V4L2_AUDCAP_AVL O Table 3 Audio Modes V4L2_AUDMODE_AVL Return Value 0x00001 0x00002 0x00001 ioctl VIDIOC_G_AUDIO VIDIOC_S_AUDIO Identifies the audio input set by the driver or application Name of the audio input a NUL terminated ASCII string for example Line In This information is intended for the user preferably the connector label on the device itself Audio capability flags see Table 2 gt Audio mode set by drivers and applications on VIDIOC_S_AUDIO ioctl see Table 3 gt Reserved for future extensions Drivers and applications must set the array to zero This is a stereo input The flag is intended to automatically disable stereo recording etc when the signal is always monaural The API provides no means to detect if stereo is received unless the audio input belongs to a tuner Automatic Volume Level mode
179. ix pixelformat V4L2_PIX_FMT_YUYV fmt pix field V4L2_FIELD_INTERLACED 1 xioctl fd VIDIOC S FMT amp fmt errno exit VIDIOC S FMT fmt fmt pix width 2 fmt fmt pix bytesperline min fmt fmt pix bytesperline min fmt fmt pix bytesperline fmt fmt pix height fmt fmt pix sizeimage min fmt fmt pix sizeimage min ch io IO METHOD READ init read fmt fmt pix sizeimage break IO METHOD MMAP init mmap break IO METHOD USERPTR init userp fmt fmt pix sizeimage break void 1 close fd errno exit close eor void struct stat st if 1 stat dev name amp st fprintf stderr Cannot identify s d s n dev name errno strerror errno exit EXIT FAILURE if S_ISCHR st st_mode fprintf stderr s is no device n dev_name exit EXIT FAILURE 209 Appendix B Video Capture Example fd open dev name O_RDWR required O NONBLOCK 0 if 1 fd fprintf stderr Cannot open s d s n dev name errno strerror errno exit EXIT_FAILURE static void usage FILE fp int argc char argv fprintf fp Usage s options n n Options Mn d device nam Video device name dev video n h help Print this message n m mmap Use memory mapped buffers Vn TEE read Use read calls n u userp
180. ld reports the smallest change of an integer control actually affecting hardware Often the information is needed when the user can change controls by keyboard or GUI buttons rather than a slider When for example a hardware register accepts values 0 511 and the driver reports 0 65535 step should be 128 Note although signed the step value is supposed to be always positive The default value of the control Drivers reset controls only when the driver is loaded not later in particular not when the open is called Control flags see Table 4 gt Reserved for future extensions Drivers must set the array to zero Identifies the control set by the application from the respective struct v412 queryctrl id Index of the menu item starting at zero set by the application Name of the menu item a NUL terminated ASCII string This information is intended for the user Reserved for future extensions Drivers must set the array to zero 139 Table 3 enum v4l2 ctrl type Type ioctl VIDIOC QUERYCTRL VIDIOC QUERYMENU Description minisinspmaximum VA4L2 CTRL TYPE INTEGER low VA4L2 CTRL TYPE BOOLEAN V4L2 CTRL TYPE MENU V4L2 CTRL TYPE BUTTON Table 4 Control Flags VAL2 CTRL FLAG DISABLED VAL2 CTRL FLAG GRABBED Return Value 0 in highAn integer valued control ranging from minimum to valuecre valuemaximum inclusive The step value indicates the incre
181. lid file descriptor EACCESS dis not open for reading and writing EINVAL The start or length or offset are not suitable E g they are too large or not aligned on a PAGESIZE boundary Or no buffers have been allocated with the VIDIOC_REQBUFS ioctl ENOMEM No memory is available 148 V4L2 munmap Name v412 munmap Unmap device memory Synopsis include lt unistd h gt include lt sys mman h gt int munmap void xstart size_t length Arguments start Address of the mapped buffer as returned by the mmap function length Length of the mapped buffer This must be the same value as given to mmap and returned by the driver in the struct v412_buffer length field Description Unmaps a previously with the mmap function mapped buffer and frees it if possible Return Value On success munmap returns 0 on failure 1 and the errno variable is set appropriately EINVAL The start or length is incorrect or no buffers have been mapped yet 149 V4L2 open Name v412 open Open a V4L2 device Synopsis include fcntl h int open const char device name int flags Arguments device name Device to be opened flags Open flags Access mode must be O_RDWR This is just a technicality input devices still support only reading and output devices only writing When the o NONBLOCK flag is given the read function and the VIDIOC_DQBUF ioctl will return
182. ltiplexing Synopsis include lt sys time h gt include lt sys types h gt include lt unistd h gt int select int n fd set readfds fd set writefds fd set xexceptfds struct timeval xtimeout Description All drivers implementing the read or write function or streaming I O must also support the select function See the select manual page for details 155 V4L2 write Name v412 write Write to a VAL2 device Synopsis include lt unistd h gt ssize_t write int fd void buf size t count Arguments fd File descriptor returned by open buf count Description write writes up to count bytes to the device referenced by the file descriptor fd from the buffer starting at buf If count is zero 0 will be returned without causing any other effect implementation tbd When the application does not provide more data in time the previous frame is displayed again Return Value On success the number of bytes written are returned Zero indicates nothing was written tbd On error 1 is returned and the errno variable is set appropriately In this case the next write will start at the beginning of a new frame Possible error codes are EAGAIN Non blocking I O has been selected using O NONBLOCK and no buffer space was available to write the data immediately tbd EBADF dis not a valid file descriptor or is not open for writing 156 V4L2 write EBUSY The driver
183. mats suitable for input to text formatters A copy made in an otherwise Transparent file format whose markup has been designed to thwart or discourage subsequent modification by readers is not Transparent A copy that is not Transparent is called Opaque Examples of suitable formats for Transparent copies include plain ASCII without markup Texinfo input format LaTeX input format SGML or XML using a publicly available DTD and standard conforming simple HTML designed for human modification Opaque formats include PostScript PDF proprietary formats that can be read and edited only by proprietary word processors SGML or XML for which the DTD and or processing tools are not generally available and the machine generated HTML produced by some word processors for output purposes only The Title Page means for a printed book the title page itself plus such following pages as are needed to hold legibly the material this License requires to appear in the title page For works in formats which do not have any title page as such Title Page means the text near the most prominent appearance of the work s title preceding the beginning of the body of the text C 3 2 VERBATIM COPYING You may copy and distribute the Document in any medium either commercially or noncommercially provided that this License the copyright notices and the license notice saying this License applies to the Document are reproduced in all copies and that you ad
184. me brew devices connected to the PC parallel port The Teletext API was designed by Martin Buck It is defined in the kernel header file linux videotext h the specification is available from http home pages de videotext Videotext is the name of the German public television Teletext service Conventional character device file names are dev vtx and dev vttuner with device number 83 0 and 83 16 respectively A similar interface exists for the Philips SAA5249 Teletext decoder specification with character device file names dev t1kN device number 102 N Eventually the Teletext API was integrated into the VAL API with character device file names dev vtx0 to dev vtx31 device major number 81 minor numbers 192 to 223 For reference the VAL Teletext API specification is reproduced here in full Teletext interfaces talk the existing VTX API Teletext devices with major number 83 and 102 will be removed in Linux 2 6 There are no plans to replace the Teletext API or to integrate it into VAL2 Please write to the Video4Linux mailing list https listman redhat com mailman listinfo video4linux list when the need arises 4 9 Radio Interface This interface is intended for AM and FM analog radio receivers Conventionally V4L2 radio devices are accessed through character device special files named dev radio and dev radio0 to dev radio63 with major number 81 and minor numbers 64 to 127 4 9 1 Querying Capabilities Devices s
185. ment between values which are actually different on the hardware ment pos i tive u32 0x0001 0x0002 A boolean valued control Zero corresponds to disabled and one means enabled The control has a menu of N choices The names of the menu items can be enumerated with the VIDIOC QUE RYM ENU ioctl A control which performs an action when set Drivers must ignore the value passed with VIDIOC S CTRL and return an EINVAL error code on a VIDIOC G CTRL attempt This control is permanently disabled and should be ignored by the application An attempt to change this control results in an EINVAL error code This control is temporarily unchangeable for example because another application took over control of the respective resource Such controls may be displayed specially in a user interface An attempt to change a grabbed control results in an EBUSY error code On success 0 is returned on error 1 and the errno variable is set appropriately EINVAL The struct v412_queryctrl id is invalid The struct v412_querymenu id or index is invalid 140 Notes 1l V4L2 CTRL FLAG DISABLED was intended for two purposes Drivers can skip predefined controls not supported by the hardware although returning EINVAL would do as well or disable predefined and custom controls after hardware detection without the trouble of reordering control arrays and indices ioctl VIDIOC QUERYST
186. n return a single flag or a set of flags as in struct v4I2 standard field id The flags must be unambiguous such that they appear in only one enumerated v412 standard structure VIDIOC S STD accepts one or more flags being a write only ioctl it does not return the actual new standard as VIDIOC_G_STD does When no flags are given or the current input does not support the requested standard the driver returns an EINVAL error code When the standard set is ambiguous drivers may return EINVAL or choose any of the requested standards Return Value On success 0 is returned on error 1 and the errno variable is set appropriately EINVAL This ioctl is not supported or the vIDIOC S STD parameter was unsuitable 124 ioctl VIDIOC G TUNER VIDIOC S TUNER Name VIDIOC G TUNER VIDIOC S TUNER Get or set tuner attributes Synopsis int ioctl int fd int request struct v412 tuner xargp int ioctl int fd int request const struct v412 tuner xargp Arguments fd File descriptor returned by open request VIDIOC G TUNER VIDIOC S5 TUNER argp Description To query the attributes of a tuner applications initialize the index field and zero out the reserved array of a struct v412 tuner and call the VIDIOC_G_TUNER ioctl with a pointer to this structure Drivers fill the rest of the structure or return an EINVAL error code when the index is out of bounds To enumerate all tuners applications shall begin at index zero i
187. ncrementing by one until the driver returns EINVAL Tuners have two writable properties the audio mode and the radio frequency To change the audio mode applications initialize the index audmode and reserved fields and call the VIDIOC S TUNER ioctl This will not change the current tuner which is determined by the current video input Drivers may choose a different audio mode if the requested mode is invalid or unsupported Since this is a write only ioctl it does not return the actually selected audio mode To change the radio frequency the vib1OC S FREQUENCY ioctl is available Table 1 struct v412_tuner u32 index Identifies the tuner set by the application u8 name 32 Name of the tuner a NUL terminated ASCII string enum v4l2 tuner type type Type of the tuner see Table 2 gt 125 u32 capability u32 rangelow u32 rangehigh u32 rxsubchans u32 audmode u32 signal 832 afc u32 reserved 4 Table 2 enum v4l2 tuner type V4L2 TUNER RADIO V4L2 TUNER ANALOG TV 2 Table 3 Tuner and Modulator Capability Flags ioctl VIDIOC G TUNER VIDIOC S TUNER Tuner capability flags see Table 3 gt Audio flags inc The lowest tunable frequency in units of 62 5 kHz The highest tunable frequency in units of 62 5 kHz Some tuners or audio decoders can determine the re V4L2 TUNER SUB MONO receiving mono at STEREO SAP
188. nds struct v4I2 rect defrect struct v412_fract pixelaspect Table 2 struct v4I2 rect 832 left 32 top 32 width 832 height Return Value ioctl VIDIOC CROPCAP Defines the window within capturing or output is possible this may exclude for example the horizontal and vertical blanking areas The cropping rectangle cannot exceed these limits Width and height are defined in pixels the driver writer is free to choose origin and units of the coordinate system in the analog domain Default cropping rectangle it shall cover the whole picture Assuming pixel aspect 1 1 this could be for example a 640 x 480 rectangle for NTSC a 768 x 576 rectangle for PAL and SECAM centered over the active picture area The same co ordinate system as for bounds is used This is the pixel aspect y x when no scaling is applied the ratio of the actual sampling frequency and the frequency required to get square pixels When cropping coordinates refer to square pixels the driver sets pixelaspect to 1 1 Other common values are 54 59 for PAL and SECAM 11 10 for NTSC sampled according to ITU601 gt Horizontal offset of the top left corner of the rectangle in pixels Vertical offset of the top left corner of the rectangle in pixels Width of the rectangle in pixels Height of the rectangle in pixels Width and height cannot be negative the fields are signed for hysterical reasons On success 0 is returned on error
189. ne VA4AL2 PIX FMT YUV422P v412 fourcc 4 2 2 P x 16 YVU422 planar x define VA4AL2 PIX FMT YUVA11P v412 fourcc 4 1 1 P x 16 YVU411 planar define V4L2_PIX_FMT_Y41P v412 fourcc Y 4 1 P x 12 YUV 4 1 1 x two planes one Y one Cr Cb interleaved define VA4L2 PIX FMT NV12 v412 fourcc N V 1 2 x 12 Y CbCr 4 2 0 x define VA4L2 PIX FMT NV21 v4l2 fourcc N twut2t T 1 7 12 YY CECB 4 2 0 x The following formats are not defined in the V4L2 specification define V4L2 PIX FMT YUV410 v412 fourcc Y U V 9 x 9 YUV 4 1 0 x define V4L2_PIX_FMT_YUV420 v412 fourcc Y U 1 2 x 12 YUV 4 2 0 x define V4L2_PIX_FMT_YYUV V2 fourco Ynyr GU OVE Pe OVO YUV 4 272 x define V4L2 PIX FMT HI240 v412 fourcc H I 2 4 8 8 bit color x see http www siliconimaging com RGB 20Bayer htm x define V4L2 PIX FMT SBGGR8 v412 fourcc B A 8 1 8 BGBG GRGR x compressed formats x define V4L2 PIX FMT MJPEG v412 fourcc M J P G Motion JPEG x define V4L2 PIX FMT JPEG v412 fourcc J P E G JFIF JPEG x define VA4L2 PIX FMT DV v412 fourcc d v s d 1394 define V4L2 PIX FMT MPEG v412 fourcc M P E G x MPEG Vendor specific formats x define V4L2_PIX_FMT_WNVA v412 fourcc W N V A x Winnov hw compress x define VA4AL2 PIX FMT SN9C10X v412 fourcc
190. ner receives the secondary language of a bilingual audio signal or a second audio program The tuner receives a Second Audio Program Note the VAL2 TUNER SUB LANG2 and V4L2 TUNER SUB SAP flags are synonyms The V4L2 TUNER SUB SAP flag applies when the current video standard is V4AL2 STD NTSC M Play mono audio When the tuner receives a stereo signal this a down mix of the left and right channel When the tuner receives a bilingual or SAP signal this mode selects the primary language Play stereo audio When the tuner receives bilingual audio it may play different languages on the left and right channel or the primary language on both channels When it receives no stereo signal or does not support stereo reception the driver shall behave as in mono mode 127 V4L2 TUNER MODE LANG1 V4L2_TUNER_MODE LANG2 V4L2_TUNER_MODE SAP Table 6 Tuner Audio Matrix ioctl VIDIOC G TUNER VIDIOC S TUNER Play the primary language mono or stereo Only V4L2 TUNI mode ER ANALOG TV tuners support this Play the secondary language mono When the tuner receives no bilingual audio or SAP or their reception is not supported the driver shall fall back to mono or stereo mode Only V4L2 TUNI mode ER ANALOG TV tuners support this Play the Second Audio Program When the tuner receives no bilingual audio or SAP or their reception is not supported t
191. no other address than the one specified If the specified address cannot be used mmap will fail If MAP FIXED is specified start must bea multiple of the pagesize Use of this option is discouraged One of the MAP SHARED or MAP PRIVATE flags must be set MAP SHARED allows to share this mapping with all other processes that map this object MAP PRIVATE requests copy on write semantics We recommend to set MAP SHARED The MAP PRIVATE MAP DENYWRITE MAP EXECUTABLE and MAP ANON flags should not be set 147 V4L2 mmap fd File descriptor returned by open offset Offset of the buffer in device memory This must be the same value as returned by the driver in the struct v412_buffer m union offset field Description The mmap function asks to map length bytes starting at offset in the memory of the device specified by d into the application address space preferably at address start This latter address is a hint only and is usually specified as 0 Suitable length and offset parameters are queried with the VIDIOC_QUERYBUF ioctl Buffers must be allocated with the VIDIOC_REQBUFS ioctl before they can be queried To unmap buffers the munmap function is used Return Value On success mmap returns a pointer to the mapped buffer On error MAP FAILED 1 is returned and the errno variable is set appropriately Possible error codes are EBADF dis not a va
192. not indicate the opposite The id must be unique No other enumerated v412 standard structure for this input or output anyway can contain the same set of bits 86 ioctl VIDIOC ENUMSTD u8 name 24 Name of the standard a NUL terminated ASCII string for example PAL B G NTSC Japan This information is intended for the user struct v412_fract frameperiod The frame period not field period is numerator denominator For example M NTSC has a frame period of 1001 30000 seconds u32 framelines Total lines per frame including blanking e g 625 for B PAL u32 reserved 4 Reserved for future extensions Drivers must set the array to zero Table 2 struct v412_fract u32 numerator u32 denominator Table 3 typedef v4I2 std id u64 v412 std id This type is a set each bit representing another video standard as listed below and in Table 4 gt The 32 most significant bits are reserved for custom driver defined video standards define V4L2 STD PAL B v412 std id 0x00000001 define VA4L2 STD PAL B1 v412 std id 0x00000002 define V4L2 STD PAL G v412 std id 0x00000004 define V4L2 STD PAL H v412 std id 0x00000008 define VA4L2 STD PAL I v412 std id 0x00000010 define V4L2 STD PAL D v412 std id 0x00000020 define VA4L2 STD PAL D1 v412 std id 0x00000040 define V4L2 STD PAL K v412 std id 0x00000080 define V4L2 STD PAL M v412 std id 0x00000100 def
193. nts must be zero 66 Chapter 4 Device Types Table 4 8 struct v412 sliced vbi data u32 id A flag from Table 2 identifying the type of data in this packet Only a single bit must be set When the id of a captured packet is zero the packet is empty and the contents of other fields are undefined Applications shall ignore empty packets When the id of a packet for output is zero the contents of the data field are undefined and the driver must no longer insert data on the requested fieldand line u32 field The video field number this data has been captured from or shall be inserted at 0 for the first field 1 for the second field u32 line The field as opposed to frame line number this data has been captured from or shall be inserted at See Figure 4 2 and Figure 4 3 for valid values Sliced VBI capture devices can set the line number of all packets to 0 if the hardware cannot reliably identify scan lines The field number must always be valid u32 reserved This field is reserved for future extensions Applications and drivers must set it to zero u8 data 48 The packet payload See Table 2 for the contents and number of bytes passed for each data type The contents of padding bytes at the end of this array are undefined drivers and applications shall ignore them Packets are always passed in ascending line number order without duplicate line numbers The write function and the VIDIOC OBUF ioctl must retu
194. numerated standard or to switch to a standard by v412 std id See Section 3 5 for a rationale Probably even USB cameras follow some well known video standard It might have been better to explicitly indicate elsewhere if a device cannot live up to normal expectations instead of this exception It will be more convenient for applications if drivers make use of the VAL2 CTRL FLAG DISABLED flag but that was never required Applications could call an ioctl to request events After another process called VIDIOC_S_CTRL or another ioctl changing shared properties the select function would indicate readability until any ioctl querying the properties is called Enumerating formats an application has no a priori knowledge of otherwise it could explicitely ask for them and need not enumerate seems useless but there are applications serving as proxy between drivers and the actual video applications for which this is useful 19 Chapter 1 Common API Elements 12 It may be desirable to refer to the cropping area in terms of sampling frequency and scanning system lines but in order to support a wide range of hardware we better make as few assumptions as possible 20 Chapter 2 Image Formats The V4L2 API was primarily designed for devices exchanging image data with applications The v412 pix format structure defines the format and layout of an image in memory Image formats are negotiated with the vibroc s rwr ioctl The explanati
195. o these functions are implemented as OSS or ALSA PCM devices and eventually OSS or ALSA audio mixer The VAL2 API makes no provisions yet to find these related devices If you have an idea please write to the Video4Linux mailing list https listman redhat com mailman listinfo video4linux list 1 1 3 Multiple Opens In general VAL2 devices can be opened more than once When this is supported by the driver users can for example start a panel application to change controls like brightness or audio volume while Chapter 1 Common API Elements another application captures video and audio In other words panel applications are comparable to an OSS or ALSA audio mixer application When a device supports multiple functions like capturing and overlay simultaneously multiple opens allow concurrent use of the device by forked processes or specialized applications Multiple opens are optional although drivers should permit at least concurrent accesses without data exchange i e panel applications This implies open can return an EBUSY error code when the device is already in use as well as ioct 1 functions initiating data exchange namely the VIDIOC S FMT ioctl and the read and write functions Mere opening a VAL2 device does not grant exclusive access Initiating data exchange however assigns the right to read or write the requested type of data and to change related properties to this file descriptor Applications can reques
196. o Cx rows including padding is exactly as long as one Y row including padding Example 2 1 VAL2 PIX FMT YUV422P 4 x 4 pixel image Byte Order Each cell is one byte start 4 0 Y oo Y oi Y o Y os start 4 Y 10 Yu Yr Yi start 8 Y o Yn Y Y start 4 12 Y 30 Y si Y 32 Ys start 4 16 Cboo Cbo start 18 Cbio Cbii start 4 20 Cboo Cboi start 4 22 Cb30 Cbs start 24 Croo Croi start 26 Crio Cru start 28 Cr20 Cra start 30 Cr30 Cr3i Color Sample Location W N e O KKK KO OO KKK KKK KN QOQO0o0n0n 33 KKK Kw VAL2 PIX FMT YUV411P 411P Name VAL2 PIX FMT YUVA411P Format with 4 horizontal chroma resolution also known as YUV 4 1 1 Planar layout as opposed to VAL2 PIX FMT YA41P Description This format is not commonly used This is a planar format similar to the 4 2 2 planar format except with half as many chroma The three components are separated into three sub images or planes The Y plane is first The Y plane has one byte per pixel The Cb plane immediately follows the Y plane in memory The Cb plane is 1 4 the width of the Y plane and of the image Each Cb belongs to 4 pixels all on the same row For example Cb belongs to Y Yor Yo and Y Following the Cb plane is the Cr plane just like the Cb plane If the Y plane has pad bytes after each row then the Cr and Cb planes have 4 as many pad bytes after their rows In other words four C x rows including p
197. o aa et gap 122 ioctl VIDIOC G STD VIDIOC S STD eese eene eee eene eo etos to eene ene sete esee en eene eo s eae eese neta 124 ioctl VIDIOC G TUNER VIDIOC S TUNER e crece eee eee eo eeo eene ene s teet to etos tns ea setae eee saneta 125 ioctl VIDIOC LOG STATUS eee retta traen ai one oar rl aea rea Fe torba epo ena ben ela ei oen aoo los count engan 129 ioctl VIDIOC OVERLAY eeeeee eee boost rotta reto n one oen rl aea song etur ba ep oi en eE Pega Sla ei oen aeo les coUa engan 130 ioctl VIDIOC QBUF VIDIOC DQBUF eere ee eee eee eene toe tn oto e tasse stent so eene en aeos eae eese neta 131 ioctl VIDIOC QUERY BUN eee eee tt rotta rae tno Ga oae eene rla aea senator ea os tas en ba bea Sla ei oen a eo ios ve sssri sisis 133 ioctl VIDIOC QUERY CAP wvcississssssessensnsosvasnssecsetasecsevasnsinecsbasesvonssbadssdebsesedssssbnsentossnsesendessssesonveds 135 ioctl VIDIOC QUERYCTRL VIDIOC_QUERYMENU scscsssssssssscsscsscssssssssscsesssessocseeees 138 ioctl VIDIOC QUERYSTD wivcicsssssssesssensnscsesnesecsetaseesevesnsinecsbacessonsssetesdebeesnsesesbncenioesssnaesdesseseseniebe 141 ioctl VIDIOC _REQBUES wiscscisssssssseessensnsosvosnssesvedasecsovssnsivecsbacessonssselesdebeesesesesincenioesssesendessesesenvees 143 ioctl VIDIOC STREAMON VIDIOC STREAMO PF eee eee ee eee eoe eere eene tn seno ense tne ene sinet 145 MIA
198. octl is optional and not all drivers support it It was introduced in Linux 2 6 15 Return Value On success 0 is returned on error 1 and the errno variable is set appropriately EINVAL The driver does not support this ioctl 129 ioctl VIDIOC OVERLAY Name VIDIOC OVERLAY Start or stop Synopsis int ioctl int fd Arguments fd int request video overlay File descriptor returned by open request VIDIOC OVERLAY argp Description This ioctl is part of the video overlay I O method Applications call VIDIOC_OV const int xargp ERLAY to start or stop the overlay It takes a pointer to an integer which must be set to zero by the application to stop overlay to one to start Drivers do not support VIDIOC STRI VAL2 BUF TYPE VIDEO OVERLAY Return Value EAMON Or VIDIOC STR EAMOFF with On success 0 is returned on error 1 and the errno variable is set appropriately EINVAL Video overlay is not supported or the parameters have not been set up See Section 4 2 for the necessary steps 130 ioctl VIDIOC QBUF VIDIOC DQBUF Name VIDIOC QBUF VIDIOC DOBUF Exchange a buffer with the driver Synopsis int ioctl int fd int request struct v412 buffer xargp Arguments fd File descriptor returned by open request VIDIOC_QBUF VIDIOC_DQBUF argp Description Applications call the vIDIOC OBUF ioctl to enqueue an empty ca
199. octl request has encoded in it whether the argument is an input output or read write parameter and the size of the argument argp in bytes Macros and defines specifying VAL2 ioctl requests are located in the videodev h header file Applications should use their own copy not include the version in the kernel sources on the system they compile on All V4L2 ioctl requests their respective function and parameters are specified in Reference I Function Reference Return Value On success the ioct1 function returns 0 and does not reset the errno variable On failure 1 is returned when the ioctl takes an output or read write parameter it remains unmodified and the errno Variable is set appropriately See below for possible error codes Generic errors like EBADF or EFAULT are not listed in the sections discussing individual ioctl requests Note ioctls may return undefined error codes Since errors may have side effects such as a driver reset applications should abort on unexpected errors 73 V4L2 ioctl EBADF dis not a valid open file descriptor EBUSY The property cannot be changed right now Typically this error code is returned when I O is in progress or the driver supports multiple opens and another process locked the property EFAULT argp references an inaccessible memory area ENOTTY fd is not associated with a character special device EINVAL The request or the data pointed to by argp is not valid This is a ve
200. ocumentation License C170 PREAXMBLE ror territi e FE ren vH es C2 1 APPLICABILITY AND DEFINITIONS eeeeeeeeeeeetreen nene nennen 212 C 3 2 VERBATIM COPYING uu 0 cccccccccccccesceeeseecesseceseececseccsesseccsseecesaecessseeecnseeeeaeecssseeens 213 CA 3 COPYINGIN OVAN iae i ete e e RR a ood eke 213 C 5 4 MODIFICATIONS sesseeeseeeeeeeene en nnne nennen nennen nee te setae se tenen nennen tene enne neni 214 C 6 5 COMBINING DOCUMENTS esses eren enne EE E enne n nnne nennt 215 C 7 6 COLLECTIONS OF DOCUMENTS esses eene eren nennen etre n tnnt 215 C 8 7 AGGREGATION WITH INDEPENDENT WORKS essere 216 978 TRANSLATION tetti re eee aee ea te eR Rees 216 10 9 TERMINATION eiecti etr E ERR Gee PEE EE b Te EE Pe NRO tess 216 C 11 10 FUTURE REVISIONS OF THIS LICENSE eese 216 CA Addendum irai Seats Ned a inge 217 Ioui 218 vi List of Tables IE eii HIP H m 10 2 1 struct vAI2 pix Torm t eor eth em epa ede en RETE t EE ent 21 2 2 enun v4l2 colorsSpace i eoe e eere biete te imei coii dette E x ve eee p duh 24 2 3 Packed RGB Image Formats eese eren enhen nennen enne nnen rennen entres 25 2 4 Reserved Image Formalts e rei erg e PEE PRU PORE PETENTE EO Ete reign 36 3 1 Str uct VAI buffer ua ee ertet ethcen cte oie 42 3 2 enunr v412 but type
201. oes VIDIOC TRY FMT is optional 4 1 4 Reading Images A video capture device may support the read function and or streaming memory mapping or user pointer I O See Chapter 3 gt for details 4 2 Video Overlay Interface Video overlay devices have the ability to genlock TV video into the VGA video signal of a graphics card or to store captured images directly in video memory of a graphics card typically with clipping This can be considerable more efficient than capturing images and displaying them by other means In the old days when only nuclear power plants needed cooling towers this used to be the only way to put live video into a window Video overlay devices are accessed through the same character special files as video capture devices Note the default function of a dev video device is video capturing The overlay function is only available after calling the VIDIOC_S_FMT ioctl The driver may support simultaneous overlay and capturing using the read write and streaming I O methods If so operation at the nominal frame rate of the video standard is not guaranteed Frames may be directed away from overlay to capture or one field may be used for overlay and the other for capture if the capture parameters permit this Applications should use different file descriptors for capturing and overlay This must be supported by all drivers capable of simultaneous capturing and overlay Optionally these drivers may also permit capturin
202. of device type All VAL2 drivers exchanging data with applications must support the O NONBLOCK flag The o_NOTO flag alias of meaningless O_TRUNC to indicate accesses without data exchange panel applications was dropped Drivers must assume panel mode until the application attempts to initiate data exchange see Section 1 1 171 Chapter 6 History 3 The struct v412 capability changed dramatically Note that also the size of the structure changed which is encoded in the ioctl request code thus older V4L2 devices will respond with an EINVAL error code to the new VIDIOC_QUERYCAP ioctl There are new fields to identify the driver a new as of yet unspecified device function VAL2 CAP RDS CAPTURE the VAL2 CAP AUDIO flag indicates if the device has any audio connectors another I O capability v4AL2 CAP ASYNCIO can be flagged Field type became a set in response to the change above and was merged with flags VAL2 FLAG TUNER was renamed to VAL2 CAP TUNER VAL2 CAP VIDEO OVERLAY replaced V4L2 FLAG PREVIEW and V4L2 CAP VBI CAPTURE and VAL2 CAP VBI OUTPUT replaced V4AL2 FLAG DATA SERVICE V4L2 FLAG READ and V4L2 FLAG WRITE merged to VAL2 CAP READWRITE Redundant fields inputs outputs audios were removed these can be determined as described in Section 1 4 and Section 1 5 The somewhat volatile and therefore barely useful fields maxwidth maxhei
203. of horizontal and vertical offset width and height In particular the driver must round the vertical offset of the cropping rectangle to frame lines modulo two such that the field order cannot be confused Second the driver adjusts the image size the opposite rectangle of the scaling process source or target depending on the data direction to the closest size possible while maintaining the current horizontal and vertical scaling factor Finally the driver programs the hardware with the actual cropping and image parameters VIDIOC S CROP is a write only ioctl it does not return the actual parameters To query them applications must call vIDIOC G CROP and VIDIOC G FMT When the parameters are unsuitable 95 ioctl VIDIOC G CROP VIDIOC S CROP the application may modify the cropping or image parameters and repeat the cycle until satisfactory parameters have been negotiated When cropping is not supported then no parameters are changed and VIDIOC S CROP returns the EINVAL error code Table 1 struct v4l2 crop enum v412 buf type type Type of the data stream set by the application Only these types are valid here V4L2 BUF TYPE VIDEO CAPTURE V4L2 BUF TYPE VIDEO OUTPUT V4L2 BUF TYPE VIDEO OVERLAY and custom driver defined types with code VAL2 BUF struct v4I2 rect c UP E_PRIVATE and higher Cropping rectangle The same co ordinate system as for struc
204. oid init mmap malloc start f stderr buffer size Out of memory Nn EXIT FAILURE void 205 Appendix B Video Capture Example struct v412 requestbuffers req CLEAR req req count 4 req type V4L2_BUF_TYPE_VIDEO_CAPTURE req memory V4L2_MEMORY_MMAP if 1 xioctl fd VIDIOC_REQBUFS amp reqg if EINVAL errno fprintf stderr Ss does not support Ww memory mapping n dev name exit EXIT FAILURE else errno exit VIDIOC REQBUFS if req count 2 fprintf stderr Insufficient buffer memory on s n dev name exit EXIT FAILURE buffers calloc req count sizeof xbuffers if buffers fprintf stderr Out of memory n exit EXIT FAILURE for n buffers 0 n buffers lt req count n buffers struct v412 buffer buf CLEAR buf buf type VA4L2 BUF TYPE VIDEO CAPTURE buf memory V4L2 MEMORY MMAP buf index n buffers if 1 xioctl fd VIDIOC QUERYBUF amp buf errno exit VIDIOC QUERYBUF buffers n buffers length buf length buffers n buffers start mmap NULL start anywhere buf length PROT READ PROT WRITE required x MAP SHARED recommended fd buf m offset if MAP FAILED buffers n_buffers start errno exit mmap 206 static
205. ome ele utet eene 68 4 9 1 Querying Capabilities ssoi terreri inos reas e ES re Ree iei 68 4 9 2 Supplemental Functions testet ee eare tiet e eier ioa 68 4 93 Programming oet eaten ee Er ete E EE 68 4 10 RDS Interface epe eet epp ta PO iet deren tempore Pari eed 68 L Function 70 VALE2 close eve dre rrr Etre ees dero Hee ia be eee REC CHE 72 VEA 73 ioctl VIDIOC CROPCAPD rete e e e eet e OR HE Ren 75 10ctl VIDIOC SENUM AUDIO 4 6 ei eite t e Rete d te deri i edis 77 ioctl VIDIOC ENUMAUDOUT Thi enn eE a E ener en nennen retener A nennen enne nenne 78 ioctl VIDIOC ENUM FM Tra n et tette eve reet et Ue epe dete ordin 79 ioctl VIDIOC ENUMINDPUT Ta nennen erinnere A A tee enne eterne entres 81 ioctl VIDIOC ENUMONNTP UT ideo petiere t iere P HERR E i rto pens 84 loct VIDIOC ENUMS TD 3 owe Pane eee 86 ioctl VIDIOC G AUDIO VIDIOC S AUDIO eerte 90 ioctl VIDIOC_G_AUDOUT VIDIOC S AUDOUT eren 92 ioctl VIDIOC G MPEGCOMP VIDIOC_S_MPEGCOMP eeeeeee eee 94 ioctl VIDIOC G CROP VIDIOC S CROP eese enne en nennen nene 95 ioctl VIDIOC G CTRE VIDIOC S CTR reinan nees erret 97 ioctl VIDIOC G FBUF VIDIOC S FBUF eere enne 99 ioctl VIDIOC G FMT VIDIOC 5 FMT VIDIOC TRY RMT nm 102 ioctl VIDIOC G FREQUENCY VIDIOC 5 FREQUENCY eee 105 ioctl VIDIOC G INPUT VID
206. omplete picture The source rectangle is set to the default when the driver is first loaded but not later The target rectangle is given either by the width and height fields of struct v412 pix format or the width and height fields of the struct v412 rect w substructure of struct v412 window In principle cropping and scaling always happens When the device supports scaling but not cropping applications will be unable to change the cropping rectangle It remains at the defaults all the time When the device supports cropping but not scaling changing the image size will also affect 15 Chapter 1 Common API Elements the cropping size in order to maintain a constant scaling factor The position of the cropping rectangle is only adjusted to move the rectangle completely inside the capture window When cropping and scaling is supported applications can change both the source and target rectangle Various hardware limitations must be expected for example discrete scaling factors different scaling abilities in horizontal and vertical direction limitations of the image size or the cropping alignment Therefore as usual drivers adjust the requested parameters against hardware capabilities and return the actual values selected An important difference because two rectangles are defined is that the last rectangle changed shall take priority and the driver may also adjust the opposite rectangle Suppose scaling is restricted to a factor 1 1 or 2
207. on field Storing strings in fixed sized arrays is bad practice but unavoidable here Drivers and applications should take precautions to never read or write beyond the end of the array and to properly terminate the strings 135 u8 card 32 u8 bus info 32 u32 version define KERNEL VERSION a b c a lt lt 16 b lt lt 8 c u32 version u32 capabilities u32 reserved 4 Table 2 Device Capabilities Flags VA4L2 CAP VIDEO CAPTURE V4L2 CAP VIDEO OUTPUT VA4L2 CAP VIDEO OVERLAY VA4L2 CAP VBI CAPTURE V4L2 CAP VBI OUTPUT VAL2 CAP RDS CAPTURE VAL2 CAP TUNER n ry ioctl VIDIOC_QUERYCAP Name of the device a NUL terminated ASCII string For example Yoyodyne TV FM Remember that one driver may support different brands or models of video hardware This information can be used to build a menu of available devices for a device select user interface Since drivers may support multiple installed devices this name should be combined with the bus_info string to avoid ambiguities Location of the device in the system a NUL terminated ASCII string For example PCI Slot 4 This information is intended for the user to distinguish multiple identical devices If no such information is available the field may simply count the devices controlled by the driver or contain the empty string bus_info 0 0 pci_dev gt slot_name example
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209. only a region of the picture and or scaled from a source image of different size To crop and scale this API defines a source and target rectangle On a video capture and overlay device the source is the received video picture the target is the captured or overlaid image On a video output device the source is the image passed by the application and the target is the generated video picture The remainder of this section refers only to video capture drivers the definitions apply to output drivers accordingly Figure 1 1 Cropping and Scaling v4I2 cropcap defrect ee v4l2_crop c v4l2_format v4l2_cropcap bounds It is assumed the driver can capture a subsection of the picture within an arbitrary capture window Its bounds are defined by struct v412_cropcap giving the coordinates of the top left corner and width and height of the window in pixels Origin and units of the coordinate system in the analog domain are arbitrarily chosen by the driver writer The source rectangle is defined by struct v412 crop giving the coordinates of its top left corner width and height using the same coordinate system as struct v412_cropcap The source rectangle must lie completely within the capture window Further each driver defines a default source rectangle The center of this rectangle shall align with the center of the active picture area of the video signal and cover what the driver writer considers the c
210. ons here focus on video capturing and output for overlay frame buffer formats see also VIDIOC G FBUF Table 2 1 struct v4l2 pix format u32 width Image width in pixels u32 height Image height in pixels Applications set these fields to request an image size drivers return the closest possible values In case of planar forma u32 pixelformat The pixel format or type of compression set by the application This is a little endian four character code VAL2 defines standard RGB formats in Table 2 3 YUV formats in Section 2 4 and reserved codes in Table 2 4 enum v412 field field Video images are typically interlaced Applications can request to capture or output only the top or bottom field or both fields interlaced or sequentially stored in one buffer or alternating in separate buffers Drivers return the actual field order selected For details see Section 3 6 u32 bytesperline Distance in bytes between the leftmost pixels in two adjacent lines Both applications and drivers can set this field to request padding bytes at the end of each line Drivers however may ig u32 sizeimage Size in bytes of the buffer to hold a complete image set by the driver Usually this is bytesperline times height When the image consists of variable length compressed data this is the maximum number of bytes required to hold an image enum v4l2 colorspace colorspace This information supplements the pixel format and must be set by the
211. onstant parameter need an update 175 6 2 11 V4L2 2003 11 05 Chapter 6 History 1 In Section 2 35 the following pixel formats were incorrectly transferred from Bill Dirks V4L2 specification Descriptions refer to bytes in memory in ascending address order Symbol In this document prior to Correct revision 0 5 VAL2 PIX FMT RGB24 B G R R G B V4L2_PIX_FMT_BGR24 R G B B G R V4L2_PIX_FMT_RGB32 IB G R X R G B X V4L2_PIX_FMT_BGR32 R G B X B G R X The v4L2_PIX_FMT_BGR24 example was always correct In Section 6 1 5 gt the mapping of VIDEO_PALETTE_RGB24 and VIDEO_PALETTE_RGB32 to V4L2 pixel formats was accordingly corrected N Unrelated to the fixes above drivers may still interpret some V4L2 RGB pixel formats differently These issues have yet to be addressed for details see Section 2 3 gt 6 2 12 V4L2 in Linux 2 6 6 2004 05 09 1 The VIDIOC_CROPCAP ioctl was incorrectly defined with read only parameter It was changed to read write while the read only version was renamed to VIDIOC_CROPCAP_OLD This function will be removed in the future 6 2 13 V4L2 in Linux 2 6 8 1 A new field input former reserved 0 was added to the struct v412_buffer structure It must be enabled with the new Vv4L2 BUF FLAG INPUT flag The flags field is no longer read only 6 2 14 V4L2 spec erratum 2004 08 01 1 The return value of the V4L2 open 2
212. open request VIDIOC G JPEGCOMP VIDIOC 5 JPEGCOMP argp Description to do Ronald Bultje elaborates APP is some application specific information The application can set it itself and it ll be stored in the JPEG encoded fields e g interlacing information for in an AVI or so COM is the same but it s comments like encoded by me or so jpeg markers describes whether the huffman tables quantization tables and the restart interval information all JPEG specific stuff should be stored in the JPEG encoded fields These define how the JPEG field is encoded If you omit them applications assume you ve used standard encoding You usually do want to add them Table 1 struct v412_jpegcompression int quality int APPn int APP len char APP data 60 109 int char u32 Table 2 JPEG Markers Flags COM len ioctl VIDIOC G JPEGCOMP VIDIOC S JPEGCOMP COM data 60 jpeg markers VAL2 JP VAL2 JP EG MARK ER DH EG MARK ER DQ VAL2 JP EG MARK ER DRI VAL2 JP EG MARK ER COM VAL2 JP EG MARK ER APP Return Value 1 3 1 4 1 5 1 lt lt 6 1 7 See Table 2 gt Define Huffman Tables Define Quantization Tables Define Restart Interval Comment segment App segment driver will always use APPO On success 0 is returned on error 1 and the errno variable is set appropriately EINVAL This ioctl is not supporte
213. or example Cr belongs to Y Yor Y ip and Y Following the Cr plane is the Cb plane just like the Cr plane v4L2_P1X_FMT_YUV420 is the same except the Cb plane comes first then the Cr plane If the Y plane has pad bytes after each row then the Cr and Cb planes have half as many pad bytes after their rows In other words two Cx rows including padding is exactly as long as one Y row including padding Example 2 1 vVAL2 PIX FMT YVU4204 x 4 pixel image Byte Order Each cell is one byte start 4 0 Y oo Y oi Y o Y os start 4 Y io Yu Yr Y 13 start 8 Y 20 Y n Y Y start 4 12 Y 30 Y s Y Y 33 start 16 Croo Croi start 18 Crio Cru start 20 Cboo Cbo start 22 Cbio Cbii Color Sample Location 0 1 2 0 Y C C 1 Y Y Y 2 Y Y Y C C 3 Y Y Y 31 VAL2 PIX FMT YVUA410 YVU9 V4L2 PIX FMT YUV410 YUV9 Name VAL2 PIX FMT YVU410 VA4L2 PIX FMT YUV410 Planar formats with 4 horizontal and vertical chroma resolution also known as YUV 4 1 0 Description These are planar formats as opposed to a packed format The three components are separated into three sub images or planes The Y plane is first The Y plane has one byte per pixel For VAL2 PIX FMT YVU410 the Cr plane immediately follows the Y plane in memory The Cr plane is 14 the width and the height of the Y plane and of the image Each Cr belongs to 16 pixels a four by four square of the image Following the Cr plane is
214. org bttv VAL2 PIX FMT MJPEG MJPG Used by the Zoran driver V4L2_PIX_FMT_JPEG JPEG unknown V4L2_PIX_FMT_DV dysd unknown V4L2_PIX_FMT_MPEG MPEG unknown VAL2 PIX FMT WNVA WNVA Used by the Winnov Videum driver http www thedirks org winnov 36 Chapter 3 Input Output The V4L2 API defines several different methods to read from or write to a device All drivers exchanging data with applications must support at least one of them The classic I O method using the read and write function is automatically selected after opening a V4L2 device When the driver does not support this method attempts to read or write will fail at any time Other methods must be negotiated To select the streaming I O method with memory mapped or user buffers applications call the VIDIOC_REQBUFS ioctl The asynchronous I O method is not defined yet Video overlay can be considered another I O method although the application does not directly receive the image data It is selected by initiating video overlay with the VIDIOC_S_FMT ioctl For more information see Section 4 2 gt Generally exactly one I O method including overlay is associated with each file descriptor The only exceptions are applications not exchanging data with a driver panel applications see Section 1 1 gt and drivers permitting simultaneous video capturing and overlay using the same file descriptor for compatibility with V4L and earlier v
215. ortant to be optional The rest should be evident 49 Chapter 3 Input Output 6 We expect that frequently used buffers are typically not swapped out Anyway the process of swapping locking or generating scatter gather lists may be time consuming The delay can be masked by the depth of the incoming buffer queue and perhaps by maintaining caches assuming a buffer will be soon enqueued again On the other hand to optimize memory usage drivers can limit the number of buffers locked in advance and recycle the most recently used buffers first Of course the pages of empty buffers in the incoming queue need not be saved to disk Output buffers must be saved on the incoming and outgoing queue because an application may share them with other processes 7 At the driver level select and po11 are the same and select is too important to be optional The rest should be evident 8 Since no other Linux multimedia API supports unadjusted time it would be foolish to introduce here We must use a universally supported clock to synchronize different media hence time of day 50 Chapter 4 Device Types 4 1 Video Capture Interface Video capture devices sample an analog video signal and store the digitized images in memory Today nearly all devices can capture at full 25 or 30 frames second With this interface applications can control the capture process and move images from the driver into user space Conventionally VAL2 video capture
216. orted the driver ignores this field its contents after calling VIDIOC S FMT are undefined When clip lists are supported but no clipping is desired this field must be set to zero When chroma keying has not been negotiated and VIDIOC G FBUF indicated this capability applications can set this field to point to a clipping bit mask It must be of the same size as the window w width and w height Each bit corresponds to a pixel in the overlaid im Notes Table 4 2 struct v4l2 clip 54 Chapter 4 Device Types struct v412 rect c Coordinates of the clipping rectangle relative to the top left corner of the frame buffer Only window pixels outside all clipping rectangles are displayed struct v4I2 clip next Pointer to the next clipping rectangle in the list NULL when this is the last rectangle Table 4 3 struct v412 rect s32 left Horizontal offset of the top left corner of the rectangle in pixels 32 top Vertical offset of the top left corner of the rectangle in pixels Offsets increase to the right and down __ 32 width Width of the rectangle in pixels __ 32 height Height of the rectangle in pixels Width and height cannot be negative the fields are signed for hysterical reasons 4 2 5 Enabling Overlay To start or stop the frame buffer overlay applications call the VIDIOC_OVERLAY ioctl 4 3 Video Output Interface Video output devices encode stills or image sequences as analog video si
217. other four Y s The Cb and Cr components have one fourth the horizontal resolution of the Y component Do not confuse this format with V4L2_PIX_FMT_YUV411P Y41P is derived from YUV 4 1 1 packed possibly in reference to a Windows FOURCC while YUV411P stands for YUV 4 1 1 planar Example 2 1 v4L2_PIX_FMT_Y41P 8 x 4 pixel image Byte Order Each cell is one byte start 0 Cbo Y o Cro Y or Cbo Y o start 12 Cbo Yr Cro Yu Cbu Y o start 24 Cbo Yo Cro You Chai Y start 36 Cb30 Y 30 Cro Ys Cbsi Yo Color Sample Location Uo N e O KKK KO KKK KR AAA KKK KN KKK Kw Croi Cru Cri Cri KKK KA Y os YB Y 5 Y a Y o4 Y u Y 54 Y a Mo oM M Y os Y is Y 25 Y ss CY OOi C 03 Y 06 Y 16 Y 26 Y 36 KKK KO Y o Yu Y n Y 37 30 KKK KN V4L2 PIX FMT YVU420 YV12 V4L2 PIX FMT YUV420 YU12 Name VA4L2 PIX FMT YVU420 VA4L2 PIX FMT YUV420 Planar formats with horizontal and vertical chroma resolution also known as YUV 4 2 0 Description These are planar formats as opposed to a packed format The three components are separated into three sub images or planes The Y plane is first The Y plane has one byte per pixel For VAL2 PIX FMT YVU420 the Cr plane immediately follows the Y plane in memory The Cr plane is half the width and half the height of the Y plane and of the image Each Cr belongs to four pixels a two by two square of the image F
218. output devices These ioctls are optional drivers need not implement them If so they return the EINVAL error code 18 Notes 10 11 Chapter 1 Common API Elements Access permissions are associated with character device special files we must ensure device numbers cannot change with load order To this end minor numbers are no longer automatically assigned by the videodev module as in V4L but requested by the driver The defaults will suffice for most people unless two drivers are used which compete for the same minor numbers In earlier versions of the V4L2 API the module options where named after the device special file with a unit prefix expressing the minor number itself not an offset Rationale for this change is unknown Lastly the naming and semantics are just a convention among driver writers the point to note is that minor numbers are not supposed to be hardcoded into drivers Given a device file name one cannot reliable find related devices For once names are arbitrary they can be chosen freely by the system administrator Also when there are multiple devices and only some support VBI capturing say dev video2 is not necessarily related to dev vbi2 We already noted finding devices by name or minor number is unreliable accordingly useful is the ioctl offered by V4L to query the minor numbers of related devices Drivers could recognize the O_EXCL open flag Presently this is not required so application canno
219. p Pointer to an enum v4l2 priority type Description To query the current access priority applications call the VIDIOC_G_PRIORITY ioctl with a pointer to an enum v4l2 priority variable where the driver stores the current priority To request an access priority applications store the desired priority in an enum v412 priority variable and call VIDIOC_S_PRIORITY ioctl with a pointer to this variable Table 1 enum v4l2 priority V4L2 PRIORITY UNSET 0 V4L2 PRIORITY BACKGROUND 1 Lowest priority usually applications running in background for example monitoring VBI transmissions A proxy application running in user space will be necessary if multiple applications want to read from a device at this priority V4L2_PRIORITY_INTERACTIVE 2 120 ioctl VIDIOC G PRIORITY VIDIOC S PRIORITY V4L2 PRIORITY DEFAULT 2 Medium priority usually applications started and interactively controlled by the user For example TV viewers Teletext browsers or just panel applications to change the channel or video controls This is the default priority unless an application requests another V4L2 PRIORITY RECORD 3 Highest priority Only one file descriptor can have this priority it blocks any other fd from changing device properties Usually applications which must not be interrupted like video recording Return Value On success 0 is returned on error 1 and the errno variable is set appropriately EINVAL The r
220. peg audiotype struct v412 bitrate st bitrate ts pid pmt ts pid audio ts pid video ts pid pcr ps size reserved 1 x align x au type au bitrate 186 2032 us u8 video enum v412 mpeg videotype enum v412 mpeg aspectratio struct v412 bitrate 1032 ul6 ue us dd misc flags Appendix A Video For Linux Two Header File au sample rate au pesig reserved 2 3 vi type vi aspect ratio vi bitrate vi frame rate vi frames per g vi bframes coun vi pesid reserved 3 3 closed gops 1 pulldown 1 reserved 4 30 20432 u32 u32 I don t expect the abov u32 i fendif struct v412 jpegcompression int quality int APPn int APP len char APP data 60 int COM len char COM data 60 u32 jpeg markers define V4L2 JPEG MARKER DHT 1 3 define V4L2 JPEG MARKER DQT 1 4 define V4L2 JPEG MARKER DRI 1 lt lt 5 define V4L2 JPEG MARKER COM 1 lt lt 6 define V4L2 JPEG MARKER APP 1 lt lt 7 M E MO R Y M AT P ING being perfect yet reserved 5 8 Number of APP segmen must be 0 15 Length of data in JP Data in the JP Length of data in JP Da EG CO ta in JP Which markers should output you do Inluding less marker leave t resulting code smaller be fewer aplications The presenc is
221. pendix or a front matter section of the Document that deals exclusively with the relationship of the publishers or authors of the Document to the Document s overall subject or to related matters and contains nothing that could fall directly within that overall subject For example if the Document is in part a textbook of mathematics a Secondary Section may not explain any mathematics The relationship could be a matter of historical connection with the subject or with related matters or of legal commercial philosophical ethical or political position regarding them The Invariant Sections are certain Secondary Sections whose titles are designated as being those of Invariant Sections in the notice that says that the Document is released under this License The Cover Texts are certain short passages of text that are listed as Front Cover Texts or Back Cover Texts in the notice that says that the Document is released under this License A Transparent copy of the Document means a machine readable copy represented in a format whose specification is available to the general public whose contents can be viewed and edited directly and straightforwardly with generic text editors or for images composed of pixels generic paint programs or for drawings some widely available drawing editor and that is suitable for input 212 Appendix C GNU Free Documentation License to text formatters or for automatic translation to a variety of for
222. pixel aspect ratio can be obtained with the VIDIOC_CROPCAP ioctl To get or set the current cropping rectangle applications call the VIDIOC G CROP or VIDIOC S CROP ioctl respectively All video capture and output devices must support the VIDIOC CROPCAP ioctl The VIDIOC_G_CROP and VIDIOC S CROP ioctls only when the cropping rectangle can be changed Note as usual the cropping parameters remain unchanged across closing and reopening a device Applications should ensure the parameters are suitable before starting I O Example 1 10 Resetting the cropping parameters A video capture device is assumed struct v412 cropcap cropcap struct v412 crop crop memset amp cropcap 0 sizeof cropcap cropcap type V4L2_BUF_TYPE_VIDEO_CAPTURE if 1 ioctl fd VIDIOC CROPCAP amp cropcap perror VIDIOC CROPCAP exit EXIT FAILURE memset amp crop 0 sizeof crop crop type V4L2_BUF_TYPE_VIDEO_CAPTURE crop c cropcap defrect Ignore if cropping is not supported EINVAL x 16 Chapter 1 Common API Elements if 1 ioctl fd VIDIOC S CROP amp crop amp amp errno EINVAL perror VIDIOC_S_CROP exit EXIT FAILURE Example 1 11 Simple downscaling A video capture device is assumed struct v412 cropcap cropcap struct v412 format format reset cropping parameters Scale down to 1 4 size of full picture mem
223. preliminary proc videodev file First draft of CODEC driver API spec 1998 11 08 Updating for many minor changes to the V4L2 spec Most symbols have been renamed Some material changes to v412 capability 1998 11 12 bugfix some of the VIDIOC symbols were not constructed with the right macros which could lead to errors on what should have been valid ioctl calls 1998 11 14 VAL2 PIX FMT RGB24 changed to V4L2_PIX_FMT_BGR24 Same for RGB32 Audio UI controls moved to VIDIOC S CTRL system and assigned VAL2 CID AUDIO symbols Removed VAL2 MAJOR from videodev h since it is only used at one place in videodev Added YUV422 and YUV411 planar formats 1998 11 28 Changed a few ioctl symbols Added stuff for codec and video output devices 167 Chapter 6 History 1999 01 14 Added raw VBI interface 1999 01 19 Removed VIDIOC_NEXTBUF ioctl 6 2 2 VAL2 Version 0 16 1999 01 31 1999 01 27 There is now one QBUF ioctl VIDIOC QWBUF and VIDIOC QRBUF are gone VIDIOC QBUF takes a v412 buffer as a parameter Added digital zoom cropping controls 6 2 3 VAL2 Version 0 18 1999 03 16 Added a v4l to VAL2 ioctl compatibility layer to videodev c Driver writers this changes how you implement your ioctl handler See the Driver Writer s Guide Added some more control id codes 6 2 4 V4L2 Version 0 19 1999 06 05 1999 03 18 Fill in the category and catname fields of v412 queryctrl objects before passing them to the driver Required a mino
224. ptor returned by open request VIDIOC G INPUT VIDIOC S INPUT argp Description To query the current video input applications call the VIDIOC_G_INPUT ioctl with a pointer to an integer where the driver stores the number of the input as in the struct v412 input index field This ioctl will fail only when there are no video inputs returning EINVAL To select a video input applications store the number of the desired input in an integer and call the VIDIOC S INPUT ioctl with a pointer to this integer Side effects are possible For example inputs may support different video standards so the driver may implicitly switch the current standard It is good practice to select an input before querying or negotiating any other parameters Information about video inputs is available using the VIDIOC_ENUMINPUT ioctl Return Value On success 0 is returned on error 1 and the errno variable is set appropriately EINVAL The number of the video input is out of bounds or there are no video inputs at all and this ioctl is not supported 107 ioctl VIDIOC G INPUT VIDIOC S INPUT EBUSY I O is in progress the input cannot be switched 108 ioctl VIDIOC G JPEGCOMP VIDIOC S JPEGCOMP Name VIDIOC G JPEGCOMP VIDIOC S JPEGCOMP Synopsis int ioctl int fd int request v412 jpegcompression argp int ioctl int fd int request const v412 jpegcompression xargp Arguments fd File descriptor returned by
225. pturing or filled output buffer in the driver s incoming queue The semantics depend on the selected I O method To enqueue a memory mapped buffer applications set the t ype field of a struct v412_buffer to the same buffer type as previously struct v412_format t ype and struct v412_requestbuffers type the memory field to V4L2_MEMORY_MMAP and the index field Valid index numbers range from zero to the number of buffers allocated with VIDIOC_REQBUFS struct v412 requestbuffers count minus one The contents of the struct v412_buffer returned by a VIDIOC_QUERYBUF ioctl will do as well When the buffer is intended for output t ype is V4L2_BUF_TYPE_VIDEO_OUTPUT or V4L2_BUF_TYPE_VBI_OUTPUT applications must also initialize the bytesused field and timestamp fields See Section 3 5 for details When VIDIOC_QBUF is called with a pointer to this structure the driver sets the vVAL2 BUF FLAG MAPPED and VAL2 BUF FLAG QUEUED flags and clears the VAL2 BUF FLAG DONE flag in the flags field or it returns an EINVAL error code To enqueue a user pointer buffer applications set the type field of a struct v412 buffer to the same buffer type as previously struct v412 format t ype and struct v412 requestbuffers t ype the memory field to vaL2 MEMORY USERPTR and the m userptr field to the address of the buffer and length to its size When the buffer is intended for output additional fields must be set as above W
226. r 3 Input Output Size of the buffer not the payload in bytes Some video capture drivers support rapid and synchronous video input changes a function useful for example in video surveillance applications For this purpose applications set the VAL2 BUF FLAG INPUT flag and this field to the number of a video input as in struct v4I2 input field index A place holder for future extensions and custom driver defined buffer types VAL2 BUF TYPE PRIVATE and higher Buffer of a video capture stream see Section 4 1 Buffer of a video output stream see Section 4 3 Buffer for video overlay see Section 4 2 Buffer of a raw VBI capture stream see Section 4 6 Buffer of a raw VBI output stream see Section 4 6 This and higher values are reserved for custom driver defined buffer types The buffer resides in device memory and has been mapped into the application s address space see Section 3 2 for details Drivers set or clear this flag when the VIDIOC QUERYBUF VIDIOC QBUF or VIDIOC DQBUF ioctl is called Set by the driver Internally drivers maintain two buffer queues an incoming and outgoing queue When this flag is set the buffer is currently on the incoming queue It automatically moves to the outgoing queue after the buffer has been filled capture devices or displayed output devices Drivers set or clear this flag when the VIDIOC_QUERYBUF ioctl is called After successful calling the V
227. r change to the VIDIOC QUERYCTRL handlers in the sample drivers 1999 03 31 Better compatibility for v41 memory capture ioctls Requires changes to drivers to fully support new compatibility features see Driver Writer s Guide and v4l2cap c Added new control IDs V4L2_CID_HFLIP _VFLIP Changed V4AL2 PIX FMT YUVA422P to _YUV422P and _YUV411P to_YUV411P 1999 04 04 Added a few more control IDs 1999 04 07 Added the button control type 1999 05 02 Fixed a typo in videodev h and added the V4L2_CTRL_FLAG_GRAYED later V4L2_CTRL_FLAG_GRABBED flag 1999 05 20 Definition of VIDIOC_G_CTRL was wrong causing a malfunction of this ioctl 1999 06 05 Changed the value of V4L2_CID_WHITENESS 6 2 5 V4L2 Version 0 20 1999 09 10 Version 0 20 introduced a number of changes not backward compatible with 0 19 and earlier The purpose was to simplify the API while at the same time make it more extensible and follow common Linux driver API conventions 1 Fixed typos in some V4L2_FMT_FLAG symbols Changed struct v412_clip to be compatible with v41 1999 08 30 Added VAL2 TUNER SUB LANGI 1999 09 05 oom All ioctl commands that took an integer argument before will now take a pointer to an integer Where it makes sense the driver will return the actual value used in the integer pointed to by the argument This is a common convention and also makes certain things easier in libv412 and other system code when the parameter to ioctl is al
228. r to an integer where the driver stores the number of the output as in the struct v412 output index field This ioctl will fail only when there are no video outputs returning the EINVAL error code To select a video output applications store the number of the desired output in an integer and call the VIDIOC S OUTPUT ioctl with a pointer to this integer Side effects are possible For example outputs may support different video standards so the driver may implicitly switch the current standard It is good practice to select an output before querying or negotiating any other parameters Information about video outputs is available using the VIDIOC_ENUMOUTPUT ioctl Return Value On success 0 is returned on error 1 and the errno variable is set appropriately EINVAL The number of the video output is out of bounds or there are no video outputs at all and this ioctl is not supported 114 ioctl VIDIOC G OUTPUT VIDIOC S OUTPUT EBUSY I O is in progress the output cannot be switched 115 ioctl VIDIOC G PARM VIDIOC S PARM Name VIDIOC G PARM VIDIOC S PARM Get or set streaming parameters Synopsis int ioctl int fd int request v412 streamparm argp Arguments fd File descriptor returned by open request VIDIOC G PARM VIDIOC S8 PARM argp Description The current video standard determines a nominal number of frames per second If less than this number of frames is to be captured or output
229. rd can be sensed with the VIDIOC_QUERYSTD ioctl Note parameter of all these ioctls is a pointer to a v412 std id type a standard set not an index into the standard enumeration Drivers must implement all video standard ioctls when the device has one or more video inputs or outputs Special rules apply to USB cameras where the notion of video standards makes little sense More generally any capture device output devices accordingly which is incapable of capturing fields or frames at the nominal rate of the video standard or where timestamps refer to the instant the field or frame was received by the driver not the capture time or Chapter 1 Common API Elements where sequence numbers refer to the frames received by the driver not the captured frames Here the driver shall set the std field of struct v412 input and struct v412 output to zero the VIDIOC G STD VIDIOC S STD VIDIOC_QUERYSTD and VIDIOC_ENUMSTD ioctls shall return the EINVAL error code Example 1 5 Information about the current video standard v412 std id std id struct v412 standard standard if 1 ioctl fd VIDIOC G STD amp std id Note when VIDIOC ENUMSTD always returns EINVAL this is no video device or it falls under the USB exception and VIDIOC G STD returning EINVAL is no error x perror VIDIOC G STD exit EXIT FAILURE memset amp standard 0 sizeof standargad standard index 0
230. re is no notion of doing anything now on a multitasking system if an application needs to synchronize with another event it should examine the struct v4I2 buffer timestamp of captured buffers or set the field before enqueuing buffers for output Drivers implementing user pointer I O must support the VIDIOC REOBUFS VIDIOC OBUF VIDIOC_DQBUF VIDIOC_STREAMON and VIDIOC STREAMOFF ioctl the select and poll function 3 4 Asynchronous I O This method is not defined yet 3 5 Buffers A buffer contains data exchanged by application and driver using one of the Streaming I O methods Only pointers to buffers are exchanged the data itself is not copied These pointers together with meta information like timestamps or field parity are stored in a struct v412_buffer argument to the VIDIOC_QUERYBUF VIDIOC_QBUF and VIDIOC DOBUF ioctl Nominally timestamps refer to the first data byte transmitted In practice however the wide range of hardware covered by the V4L2 API limits timestamp accuracy Often an interrupt routine will sample the system clock shortly after the field or frame was stored completely in memory So applications must expect a constant difference up to one field or frame period plus a small few scan lines random error The delay and error can be much larger due to compression or transmission over an external bus when the frames are not properly stamped by the sender This is frequently the case with 41
231. re work than using two fds in applications which do not Also two fd s fit the general concept of one file descriptor for each logical stream Hence as a complexity trade off drivers must support two file descriptors and may support single fd operation 2 The X Window system defines regions which are vectors of struct BoxRec short x1 yl x2 y2 with width x2 x1 and height y2 y1 so one cannot pass X11 clip lists directly 3 ASK Amplitude Shift Keying A high signal level represents a 1 bit a low level a 0 bit 69 I Function Reference Table of Contents ME bTI E 72 EB 73 ioctl VIDIO TEN B1 9 407 V n M 75 iei BI COTES D LBS EENBID CU tsa 77 iei BI COTES ENUMAUDOUT n M 78 ioctl VIDIOC ENUM OL M LR Mn 79 ioctl VIDIOC ENUMINPUT e 81 ioctl VIDIOC ENUMOVUTPUT eceoi sss foin sake seta eu ooo koi ee vo obra toes seek ae Po Pio eta sess Eee eS nb Sek se epe ee era DEOS 84 ioctl VIDIOC CE NU MS ED oi ccics sas coved casSuasselocsesdena kopiert eon eee PE Ya Eee eee epe Ee ako Nee evo anas eder sedesedectocvensaes 86 ioctl VIDIOC G AUDIO VIDIOC S AUDIO eee eeeen een ettet en eene tone tosta sens tasso sense te sns 90 ioctl VIDIOC G AUDOUT VIDIOC_S_AUDOUT cerne eee eee en eene to stato sen sen etas eo sense te sns 92 ioctl VIDIOC G MPEGCOMP VID
232. receiving stereo ai MONO STEREO receiving mono ot LANG1 LANG2 receiving bilingua MONO STEREO LANG1 receiving mono S LANG2 When the V4L2 TUNER CAP STEREO _LANG1 I The selected audio mode see Table 5 for valid val The signal strength if known ranging from 0 to 655 Automatic frequency control When the afc value i Reserved for future extensions Drivers and applicat When set tuning frequencies are expressed in units of 62 5 Hz otherwise in units of 62 5 kHz This is a multi standard tuner the video standard can or must be switched B G PAL tuners for example are typically not considered multi standard because the video standard is automatically determined from the frequency band The set of supported video standards is V4L2 TUNER CAP LOW 0x0001 V4L2 TUNER CAP NORM 0x0002 V4L2 TUNER CAP STEREO 0x0010 V4L2 TUNER CAP LANG1 0x0040 available from the struct v412_input pointing to this tuner see the description of ioctl VIDIOC ENUMINPUT for details Only V4L2 TUNER ANALOG TV tuners can have this capability Stereo audio reception is supported Reception of the primary language of a bilingual audio program is supported Bilingual audio is a feature of two channel systems transmitting the primary language monaural on the main audio carrier and a secondary language monaural on a second carrier Only V4L2 TUNER ANALOG TV tuners can have this capability
233. recorded on video tapes but also embedded in compressed formats like MPEG This field is independent of the timestamp and sequence fields u32 sequence Set by the driver counting the frames in the sequence In VAL2 FIELD ALTERNATE mode the top and bottom field have the same sequence number The count starts at zer enum v4l2 memorymemory This field must be set by applications and or drivers in accordance with the selected I O method union m u32 offset When memory is VAL2 MEMORY MMAP this is the offset of the buffer from the start of the device memory The value is returned by the driver and apart of serving as parameter to the mmap function not useful for applications See Section 3 2 for details unsigned long userptr When memory is V4L2 MEMORY USERPTR this is a pointer to the buffer casted to unsigned long type in virtual memory set by the application See Section 3 3 for details 43 u32 length u32 input u32 reserved Table 3 2 enum v4l2 buf type V4L2 BUF TYPE VID EO CAPTURE V4L2 BUF TYPE VID V4L2 BUF TYPE VID V4L2 BUF TYPE VBI CAPTURE V4L2 BUF TYPE VBI OUTPUT V4L2 BU Hj m U PE PRIVATE Table 3 3 Buffer Flags VAL2 BUF FLAG MAPP ED V4L2 BUF FLAG QUE UE EO OUTPUT 2 EO OVERLAY 3 4 0x80 0x0001 0x0002 Chapte
234. rlay window is described by a struct v412 window It defines the size of the image its position over the graphics surface and the clipping to be applied To get the current parameters applications set the type field of a struct v412_format to V4L2 BUF TYPE VIDEO OVERLAY and call the VIDIOC_G_FMT ioctl The driver fills the v412 window substructure named win Retrieving a previously programmed clipping list or bitmap is not possible To program the overlay window applications set the t ype field of a struct v4I2 format to VA4L2 BUF TYPE VIDEO OVERLAY initialize the win substructure and call the VIDIOC S FMT ioctl The driver adjusts the parameters against hardware limits and returns the actual parameters as VIDIOC G FMT does Like VIDIOC S FMT the VIDIOC TRY FMT ioctl can be used to learn about driver capabilities without actually changing driver state Unlike VIDIOC S FMT this also works after the overlay has been enabled The scaling factor of the overlaid image is implied by the width and height given in struct v41I2 window and the size of the cropping rectangle For more information see Section 1 10 53 Chapter 4 Device Types When simultaneous capturing and overlay is supported and the hardware prohibits different image and window sizes the size requested first takes precedence The attempt to capture or overlay as well VIDIOC_S_FMT may fail with an EBUSY error code or return accordingly modi
235. rn an EINVAL error code when applications violate this rule They must also return an EINVAL error code when applications pass an incorrect field or line number or a combination of field line and id which has not been negotiated with the VIDIOC G FMT or VIDIOC_S_FMT ioctl When the line numbers are unknown the driver must pass the packets in transmitted order The driver can insert empty packets with id set to zero anywhere in the packet array To assure synchronization and to distinguish from frame dropping when a captured frame does not carry any of the requested data services drivers must pass one or more empty packets When an application fails to pass VBI data in time for output the driver must output the last VPS and WSS packet again and disable the output of Closed Caption and Teletext data or output data which is ignored by Closed Caption and Teletext decoders A sliced VBI device may support read write and or streaming memory mapping and or user pointer I O The latter bears the possibility of synchronizing video and VBI data by using buffer timestamps 4 8 Teletext Interface This interface aims at devices receiving and demodulating Teletext data TELETEXT gt evaluating the Teletext packages and storing formatted pages in cache memory Such devices are usually 67 Chapter 4 Device Types implemented as microcontrollers with serial interface 1 C and can be found on older TV cards dedicated Teletext decoding cards and ho
236. rom the start of the device memory the length field its size The driver may or may not set the remaining fields and flags they are meaningless in this context The v412 buffer structure is specified in Section 3 5 Return Value On success 0 is returned on error 1 and the errno variable is set appropriately 133 ioctl VIDIOC QUERYBUF EINVAL The buffer t ype is not supported or the index is out of bounds 134 ioctl VIDIOC QUERYCAP Name VIDIOC_QUERYCAP Query device capabilities Synopsis int ioctl int fd int request struct v412 capability xargp Arguments fd File descriptor returned by open request VIDIOC QUERYCAP argp Description All V4L2 devices support the VIDIOC_QUERYCAP ioctl It is used to identify kernel devices compatible with this specification and to obtain information about individual hardware capabilities The ioctl takes a pointer to a struct v412 capability which is filled by the driver When the driver is not compatible with this specification the ioctl returns the EINVAL error code Table 1 struct v412 capability u8 driver 16 Name of the driver a unique NUL terminated ASCII string For example bttv Driver specific applications shall use this information to verify the driver identity It is also useful to work around known bugs or to print the driver name and version in an error report to aid debugging The driver version is stored in the versi
237. rptr or length are invalid ENOMEM Insufficient memory to enqueue a user pointer buffer EIO VIDIOC DOBUF failed due to an internal error Can also indicate temporary problems like signal loss Note the driver might dequeue an empty buffer despite returning an error or even stop capturing 132 ioctl VIDIOC QUERYBUF Name VIDIOC_QUERYBUF Query the status of a buffer Synopsis int ioctl int fd int request struct v412 buf Arguments fd File descriptor returned by open request VIDIOC_QUERYBUF argp Description fer xargp This ioctl is part of the memory mapping I O method It can be used to query the status of a buffer at any time after buffers have been allocated with the VIDIOC RI EQBUFS ioctl Applications set the type field of a struct v412 buffer to the same buffer type as previously struct v412_format t ype and struct v412 requestbuffers t ype and the index field Valid index numbers range from zero to the number of buffers allocated with VIDIOC_REQBUFS struct v412_requestbuffers count minus one After calling v this structure drivers return an error code or fill the rest of the structure IDIOC QUERYBUF With a pointer to In the flags field the V4L2_BUF_FLAG_MAPPED V4L2 BUF FLAG QUEUED and V4L2 BUF FLAG DONE flags will be valid The memory field will be set to V4L2_MEMORY_MMAP the m offset contains the offset of the buffer f
238. rt packets of fixed size covering one scan line each The number of packets per video frame is variable Sliced VBI capture and output devices are accessed through the same character special files as raw VBI devices When a driver supports both interfaces the default function of a dev vbi device is raw VBI capturing or output and the sliced VBI function is only available after calling the VIDIOC_S_FMT ioctl as defined below Different file descriptors must be used to pass raw and sliced VBI data simultaneously if this is supported by the driver 4 7 1 Querying Capabilities Devices supporting the sliced VBI capturing or output API set the V4L2_CAP_SLICED_VBI_CAPTURE or V4L2_CAP_SLICED_VBI_OUTPUT flag respectively in the capabilities field of struct v412 capability returned by the VIDIOC_QUERYCAP ioctl At least 64 Chapter 4 Device Types one of the read write streaming or asynchronous I O methods must be supported Sliced VBI devices may have a tuner or modulator 4 7 2 Supplemental Functions Sliced VBI devices shall support video input or output and tuner or modulator ioctls if they have these capabilities and they may support control ioctls The video standard ioctls provide information vital to program a sliced VBI device therefore must be supported 4 7 3 Sliced VBI Format Negotiation To find out which data services are supported by the hardware applications can call the VIDIOC G SLICED VBI CAP ioctl All
239. ry common error code see the individual ioctl requests listed in Reference I Function Reference for actual causes ENOMEM Insufficient memory to complete the request ERANGE The application attempted to set a control with the vIDIOC S CTRL ioctl to a value which is out of bounds 74 ioctl VIDIOC CROPCAP Name VIDIOC CROPCAP Information about the video cropping and scaling abilities Synopsis int ioctl int fd int request struct v412 cropcap xargp Arguments fd File descriptor returned by open request VIDIOC CROPCAP argp Description Applications use this function to query the cropping limits the pixel aspect of images and to calculate scale factors They set the type field of a v412_cropcap structure to the respective buffer stream type and call the VIDIOC_CROPCAP ioctl with a pointer to this structure Drivers fill the rest of the structure The results are constant except when switching the video standard Remember this switch can occur implicit when switching the video input or output Table 1 struct v4l2 cropcap enum v4 2 buf type type Type of the data stream set by the application Only these types are valid here V4L2 BUE YPE VIDEO CAPTURE V4L2 BUE YPE VIDEO OUTPUT V4L2 BUE YPE VIDEO_OVERLAY and custom driver defined types with code V4L2_BUF_ YP E_PRIVATE and higher 75 struct v4I2 rect bou
240. s extern int v412 video std construct struct v412 standard x vs int id prority handling struct v412 prio state atomic t prios 4 H char xname int v412 prio init struct v412 prio state xglobal int v412 prio change struct v412 prio state global enum v412 priority local enum v412 priority new int v412 prio open struct v412 prio state global enum v412 priority x local int v412 prio close struct v412 prio state global enum v412 priority local enum v412 priority v412 prio max struct v412 prio state global int v412 prio check struct v412 prio state global enum v412 priority x local 198 Appendix A Video For Linux Two Header File names for fancy debug output extern char v412 field names extern char v412 type names extern char v412 ioctl names Compatibility layer interfac v4ll compat module x typedef int v412 kioctl struct inode xinode struct file file unsigned int cmd void xarg int v4l compat translate ioctl struct inode xinode struct file file int cmd void arg v412 kioctl driver ioctl dendif KERNEL x endif _ LINUX VIDEODEV2 H Local variables x C basic offset 8 x End 199 Appendix B Video Capture Example x V4L2 video capture example x This program can be used and distributed without restrictions include lt stdio h gt include lt stdlib h
241. s int ioctl int fd int request v412 mpeg compression argp Arguments fd File descriptor returned by open request VIDIOC G MPEGCOMP VIDIOC 5 MPEGCOMP argp Description to do Table 1 struct v4l2 mpeg compression to do Return Value On success 0 is returned on error 1 and the errno variable is set appropriately EINVAL This ioctl is not supported 94 ioctl VIDIOC G CROP VIDIOC S CROP Name VIDIOC G CROP VIDIOC S CROP Get or set the current cropping rectangle Synopsis int ioctl int fd int request struct v412 crop argp int ioctl int fd int request const struct v412 crop xargp Arguments fd File descriptor returned by open request VIDIOC G CROP VIDIOC 5 CROP argp Description To query the cropping rectangle size and position applications set the type field of a vAI2 crop structure to the respective buffer stream type and call the vzib1oc G CROP ioctl with a pointer to this structure The driver fills the rest of the structure or returns the EINVAL error code if cropping is not supported To change the cropping rectangle applications initialize the t ype and struct v412 rect substructure named c of a v412 crop structure and call the vIDIOC S CROP ioctl with a pointer to this structure The driver first adjusts the requested dimensions against hardware limits i e the bounds given by the capture output window and it rounds to the closest possible values
242. s a buffer for capturing It also determines the image format for this buffer The ioctl returns immediately eventually with an EAGAIN error code if no video signal had been detected When the driver supports more than one buffer applications can call the ioctl multiple times and thus have multiple outstanding capture requests The VIDIOCSYNC ioctl suspends execution until a particular buffer has been filled Drivers maintain an incoming and outgoing queue VIDIOC_QBUF enqueues any empty buffer into the incoming queue Filled buffers are dequeued from the outgoing queue with the VIDIOC DOBUF ioctl To wait until filled buffers become available this function select or poll can be used The VIDIOC STREAMON ioctl must be called once after enqueuing one or more buffers to start capturing Its counterpart VIDIOC STREAMOEFF stops capturing and dequeues all buffers from both queues Applications can query the signal status if known with the VIDIOC ENUMINPUT ioctl For a more in depth discussion of memory mapping and examples see Section 3 2 6 1 10 Reading Raw VBI Data Originally the V4L API did not specify a raw VBI capture interface merely the device file dev vbi was reserved for this purpose The only driver supporting this interface was the BTTV driver de facto defining the VAL VBI interface Reading from the device yields a raw VBI image with the following parameters struct v4l2 vbi format V4L B
243. s applied videodev Changed fourcc to v412 fourcc to avoid namespace pollution Some other cleanup 2001 03 02 Certain v4l ioctls that really pass data both ways but whose types are read only did not work correctly through the backward compatibility layer Solution 2001 04 13 Added big endian 16 bit RGB formats 2001 09 17 Added new YUV formats Added VIDIOC G FREQUENCY and VIDIOC S FREQUENCY The VIDIOC G S FREQ ioctls did not take multiple tuners into account 170 Chapter 6 History 2000 09 18 Added VAL2 BUF TYPE VBI Raw VBI VIDIOC G FMT and VIDIOC S FMT may fail if field type is not VAL2 BUF TYPE VBI Changed the ambiguous phrase rising edge to leading edge in the definition of struct v412 vbi format field offset 6 2 7 VAL2 Version 0 20 2000 11 23 A number of changes were made to the raw VBI interface 1 Added figures clarifying the line numbering scheme The description of start 0 and start 1 as base 0 offset has been dropped Rationale a The previous definition was unclear b The start values are not an offset into anything as a means of identifying scanning lines it can only be counterproductive to deviate from common numbering conventions Compatibility Add one to the start values Applications depending on the previous semantics of start values may not function correctly N The restriction count 0 gt 0 and count 1 gt 0 has been relaxed to count 0 count 1 gt 0 Rationale
244. se return r yl 255 219 0 Y1 16 pb 255 224 0 Cb 128 pr 255 224 0 Cr 128 r 1 0 yl 0 pb 1 402 pr g 1 0 yl 0 344 x pb 0 714 pr b 1 0 yl 1 772 pb 0 pr ER clamp r 255 x EG clamp g 255 EB clamp b 255 Table 2 2 enum v4l2 colorspace Chapter 2 Image Formats imit yl pb pr Bt878 lextentsb ITU601 gt H 0 587 B c 0 114 B s Identifier Value DescriptionChromaticities WhiteGamma Lumi Point Correc inance Red Green Blue Y Cb Cr tion Ev l V4L2_CQLORISPACNTSIG PAL 0M E accord x 0 630x 0 310x 0 155 0 3124 5 I for I G 29018 x2 19 E v 226 Per 128 ingto ly 0 340y 0 595y 0 070y 0 3290 099 Io 43 0 587 E G SMPTEI70M Illumi 0 099 for 0 18 4H ITU601 gt Inant Des V4L2 CQLORSPAGEI2SMP TE 240M EF Line x 0 630 0 310 0 155ik 0 3124 1 for I ODZ 2219 E v 206 Psr 128 US y 0 340y 0 595y 0 070y 0 3290 1115 Io450 701 B c HDTV Illumi 0 1115 far Q 0 87 8E SI see nant Des SMPTE240M V4L2 COLORS PACH DAE 7 0 9 EF and x 0 640 0 300 0 150 0 3124 5 I for IGCDIQ 587 219 E v 206 Psr 128 modern ly 0 330y 0 600y 0 060y 0 32900 099 Io 43 0 7154 E c devices Illumi 0 099 for 0 0 08 XE s See Inant Des ITU709 gt V4L2 caLoRBPAQdBrokesm78 0 299 E R237 E v 204 Psr 1
245. service lines array explicitly The vIDIOC_S_FMT ioctl returns an EINVAL error code only when the given parameters are ambiguous otherwise it modifies the parameters according to hardware capabilities When the driver allocates resources at this point it may return an EBUSY error code if the required resources are temporarily unavailable Other resource allocation points which may return EBUSY can be the VIDIOC STREAMON ioctl and the first read write and select call Table 4 6 struct v412 sliced vbi format u32 service set If service setis non zero when passed with VIDIOC S FMT or V ul6 service lines 2 24 Applications initialize this array with sets of data services the driver Element 525 line systems 625 line systems service lines 0 l 1 1 service lines 0 2323 23 service lines l 164 314 65 Chapter 4 Device Types service lines l 23 56 336 Drivers must set service lines 0 0 and service 1ines 1 0 u32 io size Maximum number of bytes passed by one read or write call u32 reserved 2 This array is reserved for future extensions Applications and drivers Notes Table 4 7 Sliced VBI services Symbol Value Reference Lines usually Payload VAL2 SLICED TELETEXUx0901 TELETEXTPAL SECAM line 7 22 Last 42 of the 45 byte Teletext System B 320 335 second field Teletext packet that is 7 22 without clock run in and framing code lsb first transmitted V4L2_SLICED_VP
246. set amp format 0 sizeof format defaults format type V4L2_BUF_TYPE_VIDEO_CAPTURE format fmt pix width cropcap defrect width gt gt 1 format fmt pix height cropcap defrect height gt gt 1 format fmt pix pixelformat VA4L2 PIX FMT YUYV if 1 ioctl fd VIDIOC S FMT amp format perror VIDIOC S FORMAT exit EXIT FAILURE We could check now what we got the exact scaling factor or if the driver can scale at all At mere 2 1 the cropping rectangle was probably not changed x Example 1 12 Current scaling factor and pixel aspect A video capture device is assumed struct v412 cropcap cropcap struct v412 crop crop struct v412 format format double hscale vscale double aspect int dwidth dheight memset amp cropcap 0 sizeof cropcap cropcap type VA4L2 BUF TYPE VIDEO CAPTURE if 1 ioctl fd VIDIOC CROPCAP amp cropcap perror VIDIOC CROPCAP exit EXIT_FAILURE memset amp crop 0 sizeof crop 17 Chapter 1 Common API Elements crop type VA4L2 BUF TYPE VIDEO CAPTURE if 1 ioctl fd VIDIOC_G_CROP amp crop if errno EINVAL perror VIDIOC G CROP exit EXIT FAILURE Cropping not supported x crop c cropcap defrect memset amp format 0 sizeof format format fmt type V4L2_BUF_TYPE_VIDEO_CAPTURE E
247. sion 0 7 2004 09 19 Revised by mhs Fixed video standard selection control enumeration downscaling and aspect example Added read and user pointer i o to video cag Revision 0 6 2004 08 01 Revised by mhs v4l2_buffer changes added video capture example various corrections Revision 0 5 2003 11 05 Revised by mhs Pixel format erratum Revision 0 4 2003 09 17 Revised by mhs Corrected source and Makefile to generate a PDF SGML fixes Added latest API changes Closed gaps in the history chapter Revision 0 3 2003 02 05 Revised by mhs Another draft more corrections Revision 0 2 2003 01 15 Revised by mhs Second draft with corrections pointed out by Gerd Knorr Revision 0 1 2002 12 01 Revised by mhs First draft based on documentation by Bill Dirks and discussions on the VAL mailing list Table of Contents Introduction 1 Common API Elements eese eese ee reete stent ntn sn ata sn status tatnen tns ta on en sensn statu sensns tatnen sns ta nenas 1 1 1 Opening and Closing Devices sess eei eed to needed iden erede 1 1 1 1 Device Naming iere deer ER TRE En es Redes 1 151 2 Related Devices e one ett eee eet eee cbe e Sha EA E 2 1 13 Multiple Opens irre der erento esee eret debe hber dores tte 2 IS E BOIETCESRDEIEENTISMDEI P 3 L5 Bunctions 5 0533 depo RE Penn eue arte eh ROG 3 1 2 Queryang Capabilities tee o eiie elu vette idest 3 1 3 Application Priority iie eene eene
248. struct v412 input does not only indicate if the color killer is enabled but also if it is active disabling color decoding because it detects no color modulation 2 VIDIOC S PARMis a read write ioctl not write only as stated on the respective function reference page The ioctl changed in 2003 as noted above 6 2 19 VAL2 spec erratum 2006 02 03 1 In struct v412_captureparm and struct v412_outputparm the t imeperframe field gives the time in seconds not microseconds 177 Chapter 6 History 6 3 Relation of V4L2 to other Linux multimedia APIs 6 3 1 X Video Extension The X Video Extension abbreviated XVideo or just Xv is an extension of the X Window system implemented for example by the XFree86 project Its scope is similar to V4L2 an API to video capture and output devices for X clients Xv allows applications to display live video in a window send window contents to a TV output and capture or output still images in XPixmaps With their implementation XFree86 makes the extension available across many operating systems and architectures Because the driver is embedded into the X server Xv has a number of advantages over the VAL2 video overlay interface The driver can easily determine the overlay target i e visible graphics memory or off screen buffers for non destructive overlay It can program the RAMDAC for overlay scaling or color keying or the clipping functions of the video capture hardware always in sync with dr
249. t set by the application u8 name 32 Name of the video output a NUL terminated ASCII string for example Vout This information is intended for the user preferably the connector label on the device itself u32 type Type of the output see Table 2 gt 84 u32 audioset u32 modulator v412 std id std u32 reserved 4 Table 2 Output Type VA4L2 OUTPUT TYPE MODULATOR 1 V4L2 OUTPUT TYPE ANALOG 2 VA4L2 OUTPUT TYPE ANALOGVGAOV RLAY Return Value ioctl VIDIOC ENUMOUTPUT Video outputs combine with zero or more audio outputs For example one composite video connectors may exist but two audio connectors On the other hand video to a modulator will likely combine only with audio to the same modulator Devices with N audio outputs number them 0 N 1 with N x 32 Each bit position of audioset represents one audio output For details on audio outputs and how to switch see Section 1 5 Output devices can have zero or more RF modulators When the type is V4L2 OUTPUT TYPE MODULATOR this is an RF connector and this field identifies the modulator It corresponds to struct v4 2 modulator field index For details on modulators see Section 1 6 Every video output supports one or more different video standards This field is a set of all supported standards For details on video standards and how to switch see Section 1 7 Reserved for future extensions Drivers must set the array
250. t additional access privileges using the priority mechanism described in Section 1 35 1 1 4 Shared Data Streams VAL2 drivers should not support multiple applications reading or writing the same data stream on a device by copying buffers time multiplexing or similar means This is better handled by a proxy application in user space When the driver supports stream sharing anyway it must be implemented transparently The VAL2 API does not specify how conflicts are solved 1 1 5 Functions To open and close V4L2 devices applications use the open and c1ose function respectively Devices are programmed using the ioct1 function as explained in the following sections 1 2 Querying Capabilities Because V4L2 covers a wide variety of devices not all aspects of the API are equally applicable to all types of devices Furthermore devices of the same type have different capabilities and this specification permits the omission of a few complicated and less important parts of the API The VIDIOC_QUERYCAP ioctl is available to check if the kernel device is compatible with this specification and to query the functions and I O methods supported by the device Other features can be queried by calling the respective ioctl for example VIDIOC_ENUMINPUT to learn about the number types and names of video connectors on the device Although abstraction is a major objective of this API the ioctl also allows driver specific applications to reliable id
251. t as if it was a plain file Well written V4L2 applications ensure they really get what they want including cropping and scaling Cropping initialization at minimum requires to reset the parameters to defaults An example is given in Section 1 10 To query the current image format applications set the t ype field of a struct v4I2 format to V4L2 BUF TYPE VIDEO CAPTURE and call the viDIOC G FMT ioctl with a pointer to this structure Drivers fill the struct v412 pix format pix member of the fmt union To request different parameters applications set the type field of a struct v412 format as above and initialize all fields of the struct v412 pix format vbi member of the fmt union or better just modify the results of VIDIOC_G_FMT and call the VIDIOC_S_FMT ioctl with a pointer to this structure Drivers may adjust the parameters and finally return the actual parameters as VIDIOC G FMT does Like VIDIOC S rFMT the VIDIOC TRY FMT ioctl can be used to learn about hardware limitations without disabling I O or possibly time consuming hardware preparations 51 Chapter 4 Device Types The contents of struct v4l2 pix format are discussed in Chapter 2 See also the specification of the VIDIOC G FMT VIDIOC S FMT and VIDIOC TRY FWT ioctls for details Video capture devices must implement both the VIDIOC_G_FMT and VIDIOC S FMT ioctl even if VIDIOC S FMT ignores all requests and always returns default parameters as VIDIOC G FMT d
252. t different ones for VBI Experience showed this approach has several problems and to make things worse the V4L videodev module used to prohibit multiple opens of a device As a remedy the present version of the V4L2 API relaxed the concept of device types with specific names and minor numbers For compatibility with old applications drivers must still register different minor numbers to assign a default function to the device But if related functions are supported by the driver they must be available under all registered minor numbers The desired function can be selected after opening the device as described in Chapter 4 gt Imagine a driver supporting video capturing video overlay raw VBI capturing and FM radio reception It registers three devices with minor number 0 64 and 224 this numbering scheme is inherited from the VAL API Regardless if dev video 81 0 or dev vbi 81 224 is opened the application can select any one of the video capturing overlay or VBI capturing functions Without programming e g reading from the device with dd or cat dev video captures video images while dev vbi captures raw VBI data dev radio 81 64 is invariable a radio device unrelated to the video functions Being unrelated does not imply the devices can be used at the same time however The open function may very well return an EBUSY error code Besides video input or output the hardware may also support audio sampling or playback If s
253. t know if it really works Actually struct v412_audio ought to have a tuner field like struct v412 input not only making the API more consistent but also permitting radio devices with multiple tuners Some users are already confused by technical terms PAL NTSC and SECAM There is no point asking them to distinguish between B G D or K when the software or hardware can do that automatically An alternative to the current scheme is to use pointers to indices as arguments of VIDIOC G STD and VIDIOC S STD the struct v412 input and struct v412 output std field would be a set of indices like audioset Indices are consistent with the rest of the API and identify the standard unambiguously In the present scheme of things an enumerated standard is looked up by v412 std id Now the standards supported by the inputs of a device can overlap Just assume the tuner and composite input in the example above both exist on a device An enumeration of PAL B G PAL H I suggests a choice which does not exist We cannot merge or omit sets because applications would be unable to find the standards reported by vIDIOC G STD That leaves separate enumerations for each input Also selecting a standard by v412 std id can be ambiguous Advantage of this method is that applications need not identify the standard indirectly after enumerating So in summary the lookup itself is unavoidable The difference is only whether the lookup is necessary to find an e
254. t v412_cropcap bounds is used Return Value On success 0 is returned on error 1 and the errno variable is set appropriately EINVAL Cropping is not supported 96 ioctl VIDIOC G CTRL VIDIOC S CTRL Name VIDIOC G CTRL VIDIOC S CTRL Get or set the value of a control Synopsis int ioctl int fd int request struct v412 control xargp Arguments fd File descriptor returned by open request VIDIOC G CTRL VIDIOC 5 CTRL argp Description To get the current value of a control applications initialize the id field of a struct v4l2 control and call the vIDIOC G CTRL ioctl with a pointer to this structure To change the value of a control applications initialize the id and value fields of a struct v412 control and call the vIDIOC S CTRL ioctl When the id is invalid drivers return an EINVAL error code When the value is out of bounds drivers can choose to take the closest valid value or return an ERANGE error code whatever seems more appropriate However VIDIOC_S_CTRL is a write only ioctl it does not return the actual new value Table 1 struct v412_ control u32 id Identifies the control set by the application 832 value New value or current value Return Value On success 0 is returned on error 1 and the errno variable is set appropriately 97 ioctl VIDIOC G CTRL VIDIOC S CTRL EINVAL The struct v412 control id is invalid ERANGE The struct v412 control value is out of
255. ter version applies to it you have the option of following the terms and conditions either of that specified version or of any later version that has 216 Appendix C GNU Free Documentation License been published not as a draft by the Free Software Foundation If the Document does not specify a version number of this License you may choose any version ever published not as a draft by the Free Software Foundation C 12 Addendum To use this License in a document you have written include a copy of the License in the document and put the following copyright and license notices just after the title page Copyright O YEAR YOUR NAME Permission is granted to copy distribute and or modify this document under the terms of the GNU Free Documentation License Version 1 1 or any later version published by the Free Software Foundation with the Invariant Sections being LIST THEIR TITLES with the Front Cover Texts being LIST and with the Back Cover Texts being LIST A copy of the license is included in the section entitled GNU Free Documentation License If you have no Invariant Sections write with no Invariant Sections instead of saying which ones are invariant If you have no Front Cover Texts write no Front Cover Texts instead of Front Cover Texts being LIST likewise for Back Cover Texts If your document contains nontrivial examples of program code we recommend releasing these examples in parallel under your choic
256. ters are not reset at open time to permit Unix tool chains programming a device and then writing to it as if it was a plain file Well written V4L2 applications ensure they really get what they want including cropping and scaling Cropping initialization at minimum requires to reset the parameters to defaults An example is given in Section 1 10 To query the current image format applications set the t ype field of a struct v4I2 format to V4L2 BUF TYPE VIDEO OUTPUT and call the VIDIOC_G_FMT ioctl with a pointer to this structure Drivers fill the struct v412 pix format pix member of the fmt union To request different parameters applications set the type field of a struct v412 format as above and initialize all fields of the struct v412 pix format vbi member of the fmt union or better just modify the results of VIDIOC_G_FMT and call the VIDIOC_S_FMT ioctl with a pointer to this structure Drivers may adjust the parameters and finally return the actual parameters as VIDIOC G FMT does Like VIDIOC S rFMT the VIDIOC TRY FMT ioctl can be used to learn about hardware limitations without disabling I O or possibly time consuming hardware preparations The contents of struct v4l2 pix format are discussed in Chapter 2 See also the specification of the VIDIOC G FMT VIDIOC S FMT and VIDIOC TRY FMT ioctls for details Video output devices must implement both the VIDIOC_G_FMT and VIDIOC S FMT ioctl even if VIDIOC S FMT ignores
257. the Cb plane just like the Cr plane V4L2 PIX FMT YUV410 is the same except the Cb plane comes first then the Cr plane If the Y plane has pad bytes after each row then the Cr and Cb planes have 4 as many pad bytes after their rows In other words four Cx rows including padding are exactly as long as one Y row including padding Example 2 1 v4L2_PIX_FMT_yvu410 4 x 4 pixel image Byte Order Each cell is one byte start 0 Y 00 Y oi Y o Y os start 4 Y io Yu Yr Y 13 start 8 Y o Y Y 2 Y start 12 Y 30 Y s Y Y 33 start 16 Croo start 17 Cboo Color Sample Location 0 1 2 0 Y 1 Y Y Y C 2 Y Y Y 3 Y Y Y 32 VA4L2 PIX FMT YUV422P 422P Name VAL2 PIX FMT YUV422P Format with 2 horizontal chroma resolution also known as YUV 4 2 2 Planar layout as opposed to VAL2 PIX FMT YUYV Description This format is not commonly used This is a planar version of the YUYV format The three components are separated into three sub images or planes The Y plane is first The Y plane has one byte per pixel The Cb plane immediately follows the Y plane in memory The Cb plane is half the width of the Y plane and of the image Each Cb belongs to two pixels For example Cb belongs to Y Y 9 Following the Cb plane is the Cr plane just like the Cb plane 00 If the Y plane has pad bytes after each row then the Cr and Cb planes have half as many pad bytes after their rows In other words tw
258. the VIDIOC_ENUMAUDIO ioctl also contains signal status information applicable when the current audio input is queried The VIDIOC_G_AUDIO and VIDIOC_G_AUDOUT ioctl report the current audio input and output respectively Note that unlike VIDIOC_G_INPUT and VIDIOC_G_OUTPUT these ioctls return a structure as VIDIOC_ENUMAUDIO and VIDIOC ENUMAUDOUT do not just an index To select an audio input and change its properties applications call the vIDIOC S AUDIO ioctl To select an audio output which presently has no changeable properties applications call the VIDIOC S AUDOUT ioctl Drivers must implement all input ioctls when the device has one or more inputs all output ioctls when the device has one or more outputs When the device has any audio inputs or outputs the driver must set the V4L2 CAP AUDIO flag in the struct v412 capability returned by the VIDIOC_QUERYCAP ioctl Example 1 3 Information about the current audio input struct v412 audio audio memset amp audio 0 sizeof audio if 1 ioctl fd VIDIOC G AUDIO amp audio perror VIDIOC G AUDIO exit EXIT_FAILURE Chapter 1 Common API Elements printf Current input s n audio name Example 1 4 Switching to the first audio input struct v412 audio audio memset amp audio 0 sizeof audio clear audio mode audio reserved audio index 0 if 1 ioctl fd VIDIOC S AUDIO amp audio perror VIDIOC S AUDI
259. the VIDIOC_G_FMT and VIDIOC_S_FMT ioctl When the requested buffer type is not supported drivers return an EINVAL error code on a VIDIOC S rFMT attempt When I O is already in progress or the resource is not available for other reasons drivers return the EBUSY error code The VIDIOC_TRY_FMT ioctl is equivalent to VIDIOC_S_FMT with one exception it does not change driver state It can also be called at any time never returning EBUSY This function is provided to negotiate parameters to learn about hardware limitations without disabling I O or possibly time consuming hardware preparations Although strongly recommended drivers are not required to implement this ioctl Table 1 struct v412_ format enum v4 2 buf type type union fmt struct v41l2 pix format pix struct v412_ window win struct v4l2 vbi format vbi struct v412_sliced_vbi_fosmated u8 raw data 200 Return Value Type of the data stream see Table 3 2 Definition of an image format see Chapter 2 used by video capture and output devices Definition of an overlaid image see Section 4 2 used by video overlay devices Raw VBI capture or output parameters This is discussed in more detail in Section 4 62 Used by raw VBI capture and output devices Sliced VBI capture or output parameters See Section 4 7 for details Used by sliced VBI capture and output devices Place holder for future extensions and custom driver defined formats with
260. thout actually selecting a new data format The data formats supported by the VAL2 API are covered in the respective device section in Chapter 4 For a closer look at image formats see Chapter 2 gt The vIDIOC_S_FMT ioctl is a major turning point in the initialization sequence Prior to this point multiple panel applications can access the same device concurrently to select the current input change controls or modify other properties The first vIDIOC S FMT assigns a logical stream video data VBI data etc exclusively to one file descriptor Exclusive means no other application more precisely no other file descriptor can grab this stream or change device properties inconsistent with the negotiated parameters A video standard change for example when the new standard uses a different number of scan lines can invalidate the selected image format Therefore only the file descriptor owning the stream can make invalidating changes Accordingly multiple file descriptors which grabbed different logical streams prevent each other from interfering with their settings When for example video overlay is about to start or already in progress simultaneous video capturing may be restricted to the same cropping and image size When applications omit the vIDIOC S FMT ioctl its locking side effects are implied by the next step the selection of an I O method with the vVIDIOC_REQBUFS ioctl or implicit with the first read or write call Generally onl
261. tions requires special permission from their copyright holders but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections You may include a translation of this License provided that you also include the original English version of this License In case of a disagreement between the translation and the original English version of this License the original English version will prevail C 10 9 TERMINATION You may not copy modify sublicense or distribute the Document except as expressly provided for under this License Any other attempt to copy modify sublicense or distribute the Document is void and will automatically terminate your rights under this License However parties who have received copies or rights from you under this License will not have their licenses terminated so long as such parties remain in full compliance C 11 10 FUTURE REVISIONS OF THIS LICENSE The Free Software Foundation http www gnu org fsf fsf html may publish new revised versions of the GNU Free Documentation License from time to time Such new versions will be similar in spirit to the present version but may differ in detail to address new problems or concerns See http www gnu org copyleft http www gnu org copyleft Each version of the License is given a distinguishing version number If the Document specifies that a particular numbered version of this License or any la
262. to zero This output is an analog TV modulator Analog baseband output for example Composite CVBS S Video RGB On success 0 is returned on error 1 and the errno variable is set appropriately EINVAL The struct v412 output index is out of bounds 85 ioctl VIDIOC ENUMSTD Name VIDIOC_ENUMSTD Enumerate supported video standards Synopsis int ioctl int fd int request struct v412 standard xargp Arguments fd File descriptor returned by open request VIDIOC ENUMSTD argp Description To query the attributes of a video standard especially a custom driver defined one applications initialize the index field of struct v412 standard and call the VIDIOC_ENUMSTD ioctl with a pointer to this structure Drivers fill the rest of the structure or return an EINVAL error code when the index is out of bounds To enumerate all standards applications shall begin at index zero incrementing by one until the driver returns EINVAL Drivers may enumerate a different set of standards after switching the video input or output Table 1 struct v4l2 standard u32 index Number of the video standard set by the application v4l2 std id id The bits in this field identify the standard as one of the common standards listed in Table 3 or if bits 32 to 63 are set as custom standards Multiple bits can be set if the hardware does not distinguish between these standards however separate indices do
263. top __s32 width __s32 height struct v412 fract u32 numerator 38 denominator E DRIVER CAPABILITIES struct v412 capability u8 driver 16 i e bttv 7 u8 card 32 i e Hauppauge WinTV x u8 bus info 32 PCI pci name pci dev u32 version should use KERNEL VERSION 032 capabilities Device capabilities x u32 reserved 4 Values for capabilities field define V4L2_CAP_VIDEO_CAPTURE 0x00000001 Is a video capture device x define VA4L2 CAP VIDEO OUTPUT 0x00000002 x Is a video output device define V4L2 CAP VIDEO OVERLAY 0x00000004 Can do video overlay define V4L2 CAP VBI CAPTURE 0x00000010 Is a raw VBI capture device define V4L2 CAP VBI OUTPUT 0x00000020 Is a raw VBI output device if 1 KEEP define V4L2 CAP SLICED VBI CAPTURE 0x00000040 x Is a sliced VBI capture device x define V4L2 CAP SLICED VBI OUTPUT 0x00000080 x Is a sliced VBI output device endif define V4L2 CAP RDS CAPTURE 0x00000100 RDS data capture define V4L2 CAP TUNER 0x00010000 has a tuner define V4L2 CAP AUDIO 0x00020000 has audio support define V4L2 CAP RADIO 0x00040000 is a radio device x define V4L2 CAP READWRITE 0x01000000 x read write systemcalls define V4L2_CAP_ASYNCIO 0x02000000 async I O define V4L2_CAP_STREAMING 0x04000000 x streaming I O ioctls 183 Appendix A Video For Linux Two Header F
264. ts An ioctl to determine the current audio input if more than one combines with the current video input did not exist So VIDIOC G AUDIO was renamed to VIDIOC G AUDIO OLD this ioctl will be removed in the future The VIDIOC_ENUMAUDTO ioctl was added to enumerate audio inputs while VIDIOC G AUDIO now reports the current audio input The same changes were made to VIDIOC G AUDOUT and VIDIOC ENUMAUDOUT Until further the videodev module will automatically translate to the new versions drivers and applications must be updated when they are recompiled 4 The VIDIOC_OVERLAY ioctl was incorrectly defined with read write parameter It was changed to write only while the read write version was renamed to VIDIOC OVERLAY OLD This function will be removed in the future Until further the videodev module will automatically translate to the new version so drivers must be recompiled but not applications 5 Section 4 2 incorrectly stated that clipping rectangles define regions where the video can be seen Correct is that clipping rectangles define regions where no video shall be displayed and so the graphics surface can be seen 6 The VIDIOC_S_PARM and VIDIOC S CTRL were defined with write only parameter inconsistent with other ioctls modifying their argument They were changed to read write while a OLD suffix was added to the write only version These functions will be removed in the future Drivers and applications assuming a c
265. ture hardware is disabled and no input buffers are filled if there are any empty buffers in the incoming queue until VIDIOC_STREAMON has been called Accordingly the output hardware is disabled no video signal is produced until VIDIOC_STREAMON has been called The ioctl will succeed only when at least one output buffer is in the incoming queue The VIDIOC_STREAMOFF ioctl apart of aborting or finishing any DMA in progress unlocks any user pointer buffers locked in physical memory and it removes all buffers from the incoming and outgoing queues That means all images captured but not dequeued yet will be lost likewise all images enqueued for output but not transmitted yet I O returns to the same state as after calling VIDIOC_REQBUFS and can be restarted accordingly Both ioctls take a pointer to an integer the desired buffer or stream type This is the same as struct v412_requestbuffers type 145 ioctl VIDIOC STREAMON VIDIOC STREAMOFF Note applications can be preempted for unknown periods right before or after the VIDIOC STRI EAMON Or VIDIOC STRI EAMOFF calls there is no notion of starting or stopping now Buffer timestamps can be used to synchronize with other events Return Value On success 0 is returned on error 1 and the errno variable is set appropriately EINVAL Streaming I O is not supported the buffer t ype is not supported or no buffers have been allocated memory mapping or enqueued o
266. ty flags set by the driver see Table 2 u32 flags Overlay control flags set by application and driver see Table 3 gt 99 void base struct v412_pix_formatt u32 width u32 height u32 pixelformat enum v412_ field field u32 bytesperline ioctl VIDIOC_G_FBUF VIDIOC S8 FBUF Physical base address of the frame buffer the address of the pixel at coordinates 0 0 in the frame buffer This field is not used when VIDIOC G FBUF sets the V4L2 FBUF CAP EXTERNOVERLAY flag in the capability field Physical layout of the frame buffer The v412_pix_format structure is defined in Chapter 2 for clarification the fields and expected values are listed below Width of the frame buffer in pixels Height of the frame buffer in pixels When the driver clears VAL2 FBUF CAP EXTERNOVERLAY the visible portion of the frame buffer can be smaller than width and height The pixel format of the graphics surface set by the application Usually this is an RGB format for example RGB 5 6 5 but YUV formats are also permitted The behavior of the driver when requesting a compressed format is undefined See Chapter 2 for information on pixel formats This field is not used when the driver sets VAL2 FBUF CAP EXTERNOVERLAY Ignored The field order is selected with the VIDIOC_S_FMT ioctl using struct v412_ window Distance in bytes between the leftmost pixels in two adjacent l
267. uct v412 fract timeperframe x Time per frame in lus units u32 extendedmode Driver specific extensions x u32 readbuffers of buffers for read u32 reserved 4 i Flags for capability and capturemode fields define V4L2 MODE HIGHQUALITY 0x0001 High quality imaging mode define V4L2 CAP TIMEPERFRAME 0x1000 x timeperframe field is supported struct v412 outputparm u32 capability Supported modes x u32 outputmode Current mode struct v412 fract timeperframe Time per frame in seconds x 32 extendedmode Driver specific extensions u32 writebuffers of buffers for write u32 reserved 4 INPUT IMAGE CR PB NG struct v412 cropcap enum v412_buf_type struct v412 rect struct v412 rect type bounds defrect 189 struct v412 fract HH struct v412 crop enum v412 buf type struct v412 rect HH ANALOG VLD define V4 define V4 define V4 define V4 define V4 define V4 define V4 define V4 define V4 define V4 define V4 define V4 define V4 define V4 define V4 define V4 define V4 define V4 define V4 define V4 define V4 define V4 define V4 define VAI define V4I some define V4 define V4 define V4 L2 S L2 S L2 S L2 S L2 S L2 S L2 S L2_5 L2_S L2_S L2_S L2_S1 L2 S L2 S L2 S typedef u64 v412 std ig one bit for each x L2 S1 L2 S1 L2 S1 L2 S1 L2 S1 L2 S1 L2
268. upporting the radio interface set the vVAL2 CAP RADIO and VAL2 CAP TUNER flag in the capabilities field of struct v412 capability returned by the VIDIOC_QUERYCAP ioctl Other combinations of capability flags are reserved for future extensions 4 9 2 Supplemental Functions Radio devices can support controls and must support the tuner ioctls They do not support the video input or output audio input or output video standard cropping and scaling compression and streaming parameter or overlay ioctls All other ioctls and I O methods are reserved for future extensions 4 9 3 Programming Radio devices may have a couple audio controls as discussed in Section 1 8 such as a volume control possibly custom controls Further all radio devices have one tuner these are discussed in Section 1 6 with index number zero to select the radio frequency and to determine if a monaural or FM stereo program is received Drivers switch automatically between AM and FM depending on the selected frequency The VIDIOC_G_TUNER ioctl reports the supported frequency range 68 Chapter 4 Device Types 4 10 RDS Interface Notes The Radio Data System transmits supplementary information in binary format for example the station name or travel information on a inaudible audio subcarrier of a radio program This interface aims at devices capable of receiving and decoding RDS information The VAL API defines its RDS API as follows From radio dev
269. ust set it to zero This flag indicates hardware which does not properly distinguish between fields Normally the VBI image stores the first field lower scanning line numbers first in memory This may be a top or bottom field depending on the video standard When this flag is set the first or second field may be stored first however the fields are still in correct temporal order with the older field first in memory a By default the two field images will be passed sequentially all lines of the first field followed by all lines of the second field compare Section 3 6 gt V4L2_FIELD_SEQ_TB and V4L2_FIELD_SEQ_BT whether the top or bottom field is first in memory depends on the video standard When this flag is set the two fields are interlaced cf V4L2_FIELD_INTERLACED The first line of the first field followed by the first line of the second field then the two second lines and so on Such a layout may be necessary when the hardware has been programmed to capture or output interlaced video images and is unable to separate the fields for VBI capturing at the same time For simplicity setting this flag implies that both count values are equal and non zero Notes a Most VBI services transmit on both fields but some have different semantics depending on the field number 59 Figure 4 1 Line synchronization offset Line synchr pulse Line blanking White Lev
270. utput yet 146 V4L2 mmap Name v412 mmap Map device memory into application address space Synopsis include lt unistd h gt include lt sys mman h gt void mmap void start size_t length int prot int flags int fd off t offset Arguments start Map the buffer to this address in the application s address space When the MAP FIXED flag is specified start must be a multiple of the pagesize and mmap will fail when the specified address cannot be used Use of this option is discouraged applications should just specify a NULL pointer here length Length of the memory area to map This must be the same value as returned by the driver in the struct v412 buffer length field prot The prot argument describes the desired memory protection It must be set to PROT READ PROT WRITE indicating pages may be read and written This is a technicality independent of the device type and direction of data exchange Note device memory accesses may incur a performance penalty It can happen when writing to capture buffers when reading from output buffers or always When the application intends to modify buffers other I O methods may be more efficient flags The flags parameter specifies the type of the mapped object mapping options and whether modifications made to the mapped copy of the page are private to the process or are to be shared with other references MAP FIXED requests that the driver selects
271. ways a pointer The ioctl commands affected are VIDIOC PREVIEW VIDIOC STREAMON VIDIOC_STREAMOFF VIDIOC S FREQ VIDIOC S INPUT VIDIOC S8 OUTPUT VIDIOC S EFFECT For example where before you might have had code like 168 CA oO Chapter 6 History err ioctl fd VIDIOC XXX V4L2_XXX that becomes int a V4L2 XXX err ioctl fd VIDIOC XXX amp a All the different set format ioctl commands are swept into a single set format command whose parameter consists of an integer value indicating the type of format followed by the format data The same for the get format commands of course This will simplify the API by eliminating several ioctl codes and also make it possible to add additional kinds of data streams or driver private kinds of streams without having to add more set format ioctls The parameter to VIDIOC S FMT is as follows The first field is a VAL2 BUF TYPE XXX value that indicates which stream the set format is for and implicitly what type of format data After that is a union of the different format structures More can be added later without breaking backward compatibility Nonstandard driver private formats can be used by casting raw data struct v412 format u32 type union struct v412 pix format pix struct v412 vbi format vbi and so on u8 raw data 200 fmt For a get format the application fills in the type field and the driver fills in the rest What was before the ima
272. y one logical stream can be assigned to a file descriptor the exception being drivers permitting simultaneous video capturing and overlay using the same file descriptor for compatibility with V4L and earlier versions of VAL2 Switching the logical stream or returning into panel mode is possible by closing and reopening the device Drivers may support a switch using VIDIOC S FMT All drivers exchanging data with applications must support the VIDIOC G FMT and VIDIOC S FMT ioctl Implementation of the VIDIOC_TRY_FMT is highly recommended but optional 1 9 2 Image Format Enumeration Apart of the generic format negotiation functions a special ioctl to enumerate all image formats supported by video capture overlay or output devices is available The VIDIOC_ENUM_FMT ioctl must be supported by all drivers exchanging image data with applications Important Drivers are not supposed to convert image formats in kernel space They must enumerate only formats directly supported by the hardware If necessary driver writers should publish an example conversion routine or library for integration into applications 14 Chapter 1 Common API Elements 1 10 Cropping and Scaling Some video capture devices can take a subsection of the complete picture and shrink or enlarge to an image of arbitrary size We call these abilities cropping and scaling Not quite correct cropping shall also refer to the inverse process output devices showing an image in
273. yctrl id VA4L2 CID PRIVATE BASE queryctrl id if 0 ioctl fd VIDIOC QUERYCTRL amp queryctrl if queryctrl flags amp V4L2 CTRL FLAG DISABLED continue printf Control s n queryctrl name if queryctrl type V4L2 CTRL TYPE MENU enumerate menu else if errno EINVAL break perror VIDIOC_QUERYCTRL exit EXIT FAILURE M 12 Chapter 1 Common API Elements Example 1 9 Changing controls struct v412 queryctrl queryctrl struct v412 control control memset amp queryctrl 0 sizeof queryctrl queryctrl id V4L2_CID_BRIGHTNESS if 1 ioctl fd VIDIOC QUERYCTRL amp queryctrl if errno EINVAL perror VIDIOC_QUERYCTRL exit EXIT FAILURE else printf V4L2_CID_BRIGHTNESS is not supported n else if queryctrl flags amp V4L2_CTRL_FLAG_DISABLED printf V4L2_CID_BRIGHTNESS is not supported n else memset amp control 0 sizeof control control id V4L2_CID_BRIGHTNESS control value queryctrl default_value if 1 ioctl fd VIDIOC S CTRL amp control perror VIDIOC_S_CTRL exit EXIT_FAILURE memset amp control 0 sizeof control control id V4L2_CID_CONTRAST if 0 ioctl fd VIDIOC G CTRL amp control control value 1 ERANG ignored here
274. ype field of the respective struct v412 output returned by the VIDIOC_ENUMOUTPUT is set to V4L2 OUTPUT TYPE MODULATOR and its modulator field contains the index number of the modulator This specification does not define radio output devices To query and change modulator properties applications use the VIDIOC_G_MODULATOR and VIDIOC S MODULATOR ioctl Note that VIDIOC S MODULATOR does not switch the current modulator when there is more than one at all The modulator is solely determined by the current video output Drivers must support both ioctls and set the v4L2 CAP TUNER sic flag in the Chapter 1 Common API Elements struct v4I2 capability returned by the VIDIOC_QUERYCAP ioctl when the device has one or more modulators 1 6 3 Radio Frequency To get and set the tuner or modulator radio frequency applications use the VIDIOC G FREQUENCY and VIDIOC S FREQUENCY ioctl which both take a pointer to a struct v4I2 frequency These ioctls are used for TV and radio devices alike Drivers must support both ioctls when the tuner or modulator ioctls are supported or when the device is a radio device 1 6 4 Satellite Receivers To be discussed See also proposals by Peter Schlaf video4linux list 9 redhat com on 23 Oct 2002 subject Re VAL Re v412 api 1 7 Video Standards Video devices typically support one or more different video standards or variations of standards Each video input and output

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