The following chapters document the evolution of the V4L2 API, errata or extensions. They are also intended to help application and driver writers to port or update their code.

The Video For Linux API was first introduced in Linux 2.1 to unify and replace various TV and radio device related interfaces, developed independently by driver writers in prior years. Starting with Linux 2.5 the much improved V4L2 API replaces the V4L API. The support for the old V4L calls were removed from Kernel, but the library supports the conversion of a V4L API system call into a V4L2 one.

For compatibility reasons the character device file names recommended for V4L2 video capture, overlay, radio and raw vbi capture devices did not change from those used by V4L. They are listed in and below in . The teletext devices (minor range 192-223) have been removed in V4L2 and no longer exist. There is no hardware available anymore for handling pure teletext. Instead raw or sliced VBI is used. The V4L videodev module automatically assigns minor numbers to drivers in load order, depending on the registered device type. We recommend that V4L2 drivers by default register devices with the same numbers, but the system administrator can assign arbitrary minor numbers using driver module options. The major device number remains 81. Device Type File Name Minor Numbers Video capture and overlay /dev/video and /dev/bttv0 According to Documentation/devices.txt these should be symbolic links to /dev/video0. Note the original bttv interface is not compatible with V4L or V4L2. , /dev/video0 to /dev/video63 0-63 Radio receiver /dev/radio According to Documentation/devices.txt a symbolic link to /dev/radio0. , /dev/radio0 to /dev/radio63 64-127 Raw VBI capture /dev/vbi, /dev/vbi0 to /dev/vbi31 224-255 V4L prohibits (or used to prohibit) multiple opens of a device file. V4L2 drivers may support multiple opens, see for details and consequences. V4L drivers respond to V4L2 ioctls with an &EINVAL;.

The V4L VIDIOCGCAP ioctl is equivalent to V4L2's &VIDIOC-QUERYCAP;. The name field in struct video_capability became card in &v4l2-capability;, 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 for an introduction. struct video_capability type &v4l2-capability; capabilities flags Purpose VID_TYPE_CAPTURE V4L2_CAP_VIDEO_CAPTURE The video capture interface is supported. VID_TYPE_TUNER V4L2_CAP_TUNER The device has a tuner or modulator. VID_TYPE_TELETEXT V4L2_CAP_VBI_CAPTURE The raw VBI capture interface is supported. VID_TYPE_OVERLAY V4L2_CAP_VIDEO_OVERLAY The video overlay interface is supported. VID_TYPE_CHROMAKEY V4L2_FBUF_CAP_CHROMAKEY in field capability of &v4l2-framebuffer; Whether chromakey overlay is supported. For more information on overlay see . VID_TYPE_CLIPPING V4L2_FBUF_CAP_LIST_CLIPPING and V4L2_FBUF_CAP_BITMAP_CLIPPING in field capability of &v4l2-framebuffer; Whether clipping the overlaid image is supported, see . VID_TYPE_FRAMERAM V4L2_FBUF_CAP_EXTERNOVERLAY not set in field capability of &v4l2-framebuffer; Whether overlay overwrites frame buffer memory, see . VID_TYPE_SCALES - This flag indicates if the hardware can scale images. The V4L2 API implies the scale factor by setting the cropping dimensions and image size with the &VIDIOC-S-CROP; and &VIDIOC-S-FMT; ioctl, respectively. The driver returns the closest sizes possible. For more information on cropping and scaling see . VID_TYPE_MONOCHROME - Applications can enumerate the supported image formats with the &VIDIOC-ENUM-FMT; ioctl to determine if the device supports grey scale capturing only. For more information on image formats see . VID_TYPE_SUBCAPTURE - 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;. For more information on cropping and scaling see . VID_TYPE_MPEG_DECODER - Applications can enumerate the supported image formats with the &VIDIOC-ENUM-FMT; ioctl to determine if the device supports MPEG streams. VID_TYPE_MPEG_ENCODER - See above. VID_TYPE_MJPEG_DECODER - See above. VID_TYPE_MJPEG_ENCODER - See above. The audios field was replaced by capabilities flag V4L2_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 . 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, taking into account the current video standard, cropping and scaling limitations.

V4L provides the VIDIOCGCHAN and VIDIOCSCHAN ioctl using struct video_channel to enumerate the video inputs of a V4L device. The equivalent V4L2 ioctls are &VIDIOC-ENUMINPUT;, &VIDIOC-G-INPUT; and &VIDIOC-S-INPUT; using &v4l2-input; as discussed in . The channel field counting inputs was renamed to index, the video input types were renamed as follows: struct video_channel type &v4l2-input; type VIDEO_TYPE_TV V4L2_INPUT_TYPE_TUNER VIDEO_TYPE_CAMERA V4L2_INPUT_TYPE_CAMERA Unlike the tuners field expressing the number of tuners of this input, V4L2 assumes each video input is connected to at most one tuner. However a tuner can have more than one input, &ie; RF connectors, and a device can have multiple tuners. The index number of the tuner associated with the input, if any, is stored in field tuner of &v4l2-input;. Enumeration of tuners is discussed in . The redundant VIDEO_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 between them see . The norm field describing the supported video standards was replaced by std. The V4L 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 for more information.

The V4L VIDIOCGTUNER and VIDIOCSTUNER ioctl and struct video_tuner can be used to enumerate the tuners of a V4L TV or radio device. The equivalent V4L2 ioctls are &VIDIOC-G-TUNER; and &VIDIOC-S-TUNER; using &v4l2-tuner;. Tuners are covered in . 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 &v4l2-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 . 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_MODE_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 &v4l2-tuner; for details. Presently no replacement exists for the VIDEO_TUNER_RDS_ON and VIDEO_TUNER_MBS_ON flags. The VIDEO_TUNER_LOW flag was renamed to V4L2_TUNER_CAP_LOW in the &v4l2-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 &v4l2-frequency; instead of an unsigned long integer.

V4L2 has no equivalent of the VIDIOCGPICT and VIDIOCSPICT ioctl and struct video_picture. The following fields where replaced by V4L2 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. The V4L2 API permits arbitrary limits and defaults which can be queried with the &VIDIOC-QUERYCTRL; ioctl. For general information about controls see . 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 &v4l2-pix-format;: struct video_picture palette &v4l2-pix-format; pixfmt VIDEO_PALETTE_GREY V4L2_PIX_FMT_GREY VIDEO_PALETTE_HI240 V4L2_PIX_FMT_HI240 This is a custom format used by the BTTV driver, not one of the V4L2 standard formats. VIDEO_PALETTE_RGB565 V4L2_PIX_FMT_RGB565 VIDEO_PALETTE_RGB555 V4L2_PIX_FMT_RGB555 VIDEO_PALETTE_RGB24 V4L2_PIX_FMT_BGR24 VIDEO_PALETTE_RGB32 V4L2_PIX_FMT_BGR32 Presumably all V4L RGB formats are little-endian, although some drivers might interpret them according to machine endianness. V4L2 defines little-endian, big-endian and red/blue swapped variants. For details see . VIDEO_PALETTE_YUV422 V4L2_PIX_FMT_YUYV VIDEO_PALETTE_YUYV VIDEO_PALETTE_YUV422 and VIDEO_PALETTE_YUYV are the same formats. Some V4L drivers respond to one, some to the other. V4L2_PIX_FMT_YUYV VIDEO_PALETTE_UYVY V4L2_PIX_FMT_UYVY VIDEO_PALETTE_YUV420 None VIDEO_PALETTE_YUV411 V4L2_PIX_FMT_Y41P Not to be confused with V4L2_PIX_FMT_YUV411P, which is a planar format. VIDEO_PALETTE_RAW None V4L explains this as: "RAW capture (BT848)" VIDEO_PALETTE_YUV422P V4L2_PIX_FMT_YUV422P VIDEO_PALETTE_YUV411P V4L2_PIX_FMT_YUV411P Not to be confused with V4L2_PIX_FMT_Y41P, which is a packed format. VIDEO_PALETTE_YUV420P V4L2_PIX_FMT_YVU420 VIDEO_PALETTE_YUV410P V4L2_PIX_FMT_YVU410 V4L2 image formats are defined in . The image format can be selected with the &VIDIOC-S-FMT; ioctl.

The VIDIOCGAUDIO and VIDIOCSAUDIO ioctl and struct video_audio are used to enumerate the audio inputs of a V4L device. The equivalent V4L2 ioctls are &VIDIOC-G-AUDIO; and &VIDIOC-S-AUDIO; using &v4l2-audio; as discussed in . 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_LANG1 or VIDEO_SOUND_LANG2 audio demodulation modes. When the current audio standard is BTSC VIDEO_SOUND_LANG2 refers to SAP and VIDEO_SOUND_LANG1 is meaningless. Also undocumented in the V4L 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 V4L2 API this information is stored in the &v4l2-tuner; rxsubchans and audmode fields, respectively. See for more information on tuners. Related to audio modes &v4l2-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 volume V4L2_CID_AUDIO_VOLUME bass V4L2_CID_AUDIO_BASS treble V4L2_CID_AUDIO_TREBLE balance V4L2_CID_AUDIO_BALANCE To determine which of these controls are supported by a driver V4L provides the flags 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 .

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 defines a flag to indicate non-destructive overlays instead of a NULL pointer. All other fields moved into the &v4l2-pix-format; fmt substructure of &v4l2-framebuffer;. The depth field was replaced by pixelformat. See for a list of RGB formats and their respective color depths. Instead of the special ioctls VIDIOCGWIN and VIDIOCSWIN V4L2 uses the general-purpose data format negotiation ioctls &VIDIOC-G-FMT; and &VIDIOC-S-FMT;. They take a pointer to a &v4l2-format; as argument. Here the win member of the fmt union is used, a &v4l2-window;. The x, y, width and height fields of struct video_window moved into &v4l2-rect; substructure w of struct v4l2_window. The chromakey, clips, and clipcount fields remained unchanged. Struct video_clip was renamed to &v4l2-clip;, also containing a struct v4l2_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 &v4l2-framebuffer;, under the new name V4L2_FBUF_FLAG_CHROMAKEY. In V4L, storing a bitmap pointer in clips and setting clipcount to VIDEO_CLIP_BITMAP (-1) requests bitmap clipping, using a fixed size bitmap of 1024 × 625 bits. Struct v4l2_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;.

To capture only a subsection of the full picture V4L defines the VIDIOCGCAPTURE and VIDIOCSCAPTURE ioctls using struct video_capture. The equivalent V4L2 ioctls are &VIDIOC-G-CROP; and &VIDIOC-S-CROP; using &v4l2-crop;, and the related &VIDIOC-CROPCAP; ioctl. This is a rather complex matter, see for details. The x, y, width and height fields moved into &v4l2-rect; substructure c of struct v4l2_crop. The decimation field was dropped. In the V4L2 API 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 field of &v4l2-pix-format; and &v4l2-window;. These structures are used to select a capture or overlay format with the &VIDIOC-S-FMT; ioctl.

There is no essential difference between reading images from a V4L or V4L2 device using the &func-read; function, however V4L2 drivers are not required to support this I/O method. Applications can determine if the function is available with the &VIDIOC-QUERYCAP; ioctl. All V4L2 devices exchanging data with applications must support the &func-select; and &func-poll; functions. To select an image format and size, V4L provides the VIDIOCSPICT and VIDIOCSWIN ioctls. V4L2 uses the general-purpose data format negotiation ioctls &VIDIOC-G-FMT; and &VIDIOC-S-FMT;. They take a pointer to a &v4l2-format; as argument, here the &v4l2-pix-format; named pix of its fmt union is used. For more information about the V4L2 read interface see .

Applications can read from V4L 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 copying 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. Applications cannot change the number of buffers. The it is built into the driver, unless it has a module option to change the number when the driver module is loaded. The &VIDIOC-REQBUFS; ioctl allocates the desired number of buffers, this is a required step in the initialization sequence. Drivers map all buffers as one contiguous range of 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 for the &func-mmap; function. Buffers are individually mapped. The offset and size of each buffer can be determined with the &VIDIOC-QUERYBUF; ioctl. The VIDIOCMCAPTURE ioctl prepares a buffer for capturing. It also determines the image format for this buffer. The ioctl returns immediately, eventually with an &EAGAIN; 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-DQBUF; ioctl. To wait until filled buffers become available this function, &func-select; or &func-poll; can be used. The &VIDIOC-STREAMON; ioctl must be called once after enqueuing one or more buffers to start capturing. Its counterpart &VIDIOC-STREAMOFF; 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 .

Originally the V4L API did not specify a raw VBI capture interface, only the device file /dev/vbi was reserved for this purpose. The only driver supporting this interface was the BTTV driver, de-facto defining the V4L VBI interface. Reading from the device yields a raw VBI image with the following parameters: &v4l2-vbi-format; V4L, BTTV driver sampling_rate 28636363 Hz NTSC (or any other 525-line standard); 35468950 Hz PAL and SECAM (625-line standards) offset ? samples_per_line 2048 sample_format V4L2_PIX_FMT_GREY. The last four bytes (a machine endianness integer) contain a frame counter. start[] 10, 273 NTSC; 22, 335 PAL and SECAM count[] 16, 16Old driver versions used different values, eventually the custom BTTV_VBISIZE ioctl was added to query the correct values. flags 0 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 . An offset field does not exist, sample_format is supposed to be VIDEO_PALETTE_RAW, equivalent to V4L2_PIX_FMT_GREY. The remaining fields are probably equivalent to &v4l2-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 &func-open; and VIDIOCSVBIFMT always returns an &EINVAL; if the parameters are invalid.

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 and requesting VBI data. For details see . No replacement exists for VIDIOCKEY, and the V4L functions for microcode programming. A new interface for MPEG compression and playback devices is documented in .

Soon after the V4L API was added to the kernel it was criticised as too inflexible. In August 1998 Bill Dirks proposed a number of improvements and began to work on documentation, example drivers and applications. With the help of other volunteers this eventually became the V4L2 API, not just an extension but a replacement for the V4L 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.

1998-08-20: First version. 1998-08-27: The &func-select; function was introduced. 1998-09-10: New video standard interface. 1998-09-18: The VIDIOC_NONCAP ioctl was replaced by the otherwise meaningless O_TRUNC &func-open; flag, and the aliases O_NONCAP and O_NOIO were defined. Applications can set this flag if they intend to access controls only, as opposed to capture applications which need exclusive access. The VIDEO_STD_XXX identifiers are now ordinals instead of flags, and the video_std_construct() helper function takes id and transmission arguments. 1998-09-28: Revamped video standard. Made video controls individually enumerable. 1998-10-02: The id field was removed from struct video_standard and the color subcarrier fields were renamed. The &VIDIOC-QUERYSTD; ioctl was renamed to &VIDIOC-ENUMSTD;, &VIDIOC-G-INPUT; to &VIDIOC-ENUMINPUT;. A first draft of the Codec API was released. 1998-11-08: Many minor changes. Most symbols have been renamed. Some material changes to &v4l2-capability;. 1998-11-12: The read/write directon of some ioctls was misdefined. 1998-11-14: V4L2_PIX_FMT_RGB24 changed to V4L2_PIX_FMT_BGR24, and V4L2_PIX_FMT_RGB32 changed to V4L2_PIX_FMT_BGR32. Audio controls are now accessible with the &VIDIOC-G-CTRL; and &VIDIOC-S-CTRL; ioctls under names starting with V4L2_CID_AUDIO. The V4L2_MAJOR define was removed from videodev.h since it was only used once in the videodev kernel module. The YUV422 and YUV411 planar image formats were added. 1998-11-28: A few ioctl symbols changed. Interfaces for codecs and video output devices were added. 1999-01-14: A raw VBI capture interface was added. 1999-01-19: The VIDIOC_NEXTBUF ioctl was removed.

1999-01-27: There is now one QBUF ioctl, VIDIOC_QWBUF and VIDIOC_QRBUF are gone. VIDIOC_QBUF takes a v4l2_buffer as a parameter. Added digital zoom (cropping) controls.

Added a v4l to V4L2 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.

1999-03-18: Fill in the category and catname fields of v4l2_queryctrl objects before passing them to the driver. Required a minor change to the VIDIOC_QUERYCTRL handlers in the sample drivers. 1999-03-31: Better compatibility for v4l 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 V4L2_PIX_FMT_YUV422P 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.

Version 0.20 introduced a number of changes which were not backward compatible with 0.19 and earlier versions. Purpose of these changes was to simplify the API, while making it more extensible and following common Linux driver API conventions. Some typos in V4L2_FMT_FLAG symbols were fixed. &v4l2-clip; was changed for compatibility with v4l. (1999-08-30) V4L2_TUNER_SUB_LANG1 was added. (1999-09-05) All ioctl() commands that used an integer argument now take a pointer to an integer. Where it makes sense, ioctls will return the actual new value in the integer pointed to by the argument, a common convention in the V4L2 API. The affected ioctls are: VIDIOC_PREVIEW, VIDIOC_STREAMON, VIDIOC_STREAMOFF, VIDIOC_S_FREQ, VIDIOC_S_INPUT, VIDIOC_S_OUTPUT, VIDIOC_S_EFFECT. For example err = ioctl (fd, VIDIOC_XXX, V4L2_XXX); becomes int a = V4L2_XXX; err = ioctl(fd, VIDIOC_XXX, &a); All the different get- and set-format commands were swept into one &VIDIOC-G-FMT; and &VIDIOC-S-FMT; ioctl taking a union and a type field selecting the union member as parameter. Purpose is to simplify the API by eliminating several ioctls and to allow new and driver private data streams without adding new ioctls. This change obsoletes the following ioctls: VIDIOC_S_INFMT, VIDIOC_G_INFMT, VIDIOC_S_OUTFMT, VIDIOC_G_OUTFMT, VIDIOC_S_VBIFMT and VIDIOC_G_VBIFMT. The image format structure v4l2_format was renamed to &v4l2-pix-format;, while &v4l2-format; is now the envelopping structure for all format negotiations. Similar to the changes above, the VIDIOC_G_PARM and VIDIOC_S_PARM ioctls were merged with VIDIOC_G_OUTPARM and VIDIOC_S_OUTPARM. A type field in the new &v4l2-streamparm; selects the respective union member. This change obsoletes the VIDIOC_G_OUTPARM and VIDIOC_S_OUTPARM ioctls. Control enumeration was simplified, and two new control flags were introduced and one dropped. The catname field was replaced by a group field. Drivers can now flag unsupported and temporarily unavailable controls with V4L2_CTRL_FLAG_DISABLED and V4L2_CTRL_FLAG_GRABBED respectively. The group name indicates a possibly narrower classification than the category. In other words, there may be 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 may even appear in separate windows. The &v4l2-buffer; timestamp was changed to a 64 bit integer, containing the sampling or output time of the frame in nanoseconds. Additionally timestamps will be in absolute system time, not starting from zero at the beginning of a stream. 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://web.archive.org/web/*/http://reality.sgi.com /cpirazzi_engr/lg/time/intro.html. 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-bit integer, and I will change the v4l2_masterclock_gettime() function (used only by drivers) to return a 64-bit integer. A sequence field was added to &v4l2-buffer;. The sequence field counts captured frames, it is ignored by output devices. When a capture driver drops a frame, the sequence number of that frame is skipped.

1999-12-23: In &v4l2-vbi-format; the reserved1 field became offset. Previously drivers were required to clear the reserved1 field. 2000-01-13: The V4L2_FMT_FLAG_NOT_INTERLACED flag was added. 2000-07-31: The linux/poll.h header is now included by videodev.h for compatibility with the original videodev.h file. 2000-11-20: V4L2_TYPE_VBI_OUTPUT and V4L2_PIX_FMT_Y41P were added. 2000-11-25: V4L2_TYPE_VBI_INPUT was added. 2000-12-04: A couple typos in symbol names were fixed. 2001-01-18: To avoid namespace conflicts the fourcc macro defined in the videodev.h header file was renamed to v4l2_fourcc. 2001-01-25: A possible driver-level compatibility problem between the videodev.h file in Linux 2.4.0 and the videodev.h file included in the videodevX patch was fixed. Users of an earlier version of videodevX on Linux 2.4.0 should recompile their V4L and V4L2 drivers. 2001-01-26: A possible kernel-level incompatibility between the videodev.h file in the videodevX patch and the videodev.h file in Linux 2.2.x with devfs patches applied was fixed. 2001-03-02: Certain V4L ioctls which pass data in both direction although they are defined with read-only parameter, did not work correctly through the backward compatibility layer. [Solution?] 2001-04-13: Big endian 16-bit RGB formats were added. 2001-09-17: New YUV formats and the &VIDIOC-G-FREQUENCY; and &VIDIOC-S-FREQUENCY; ioctls were added. (The old VIDIOC_G_FREQ and VIDIOC_S_FREQ ioctls did not take multiple tuners into account.) 2000-09-18: V4L2_BUF_TYPE_VBI was added. This may break compatibility as the &VIDIOC-G-FMT; and &VIDIOC-S-FMT; ioctls may fail now if the struct v4l2_fmt type field does not contain V4L2_BUF_TYPE_VBI. In the documentation of the &v4l2-vbi-format; offset field the ambiguous phrase "rising edge" was changed to "leading edge".

A number of changes were made to the raw VBI interface. Figures clarifying the line numbering scheme were added to the V4L2 API specification. The start[0] and start[1] fields no longer count line numbers beginning at zero. Rationale: a) The previous definition was unclear. b) The start[] values are ordinal numbers. c) There is no point in inventing a new line numbering scheme. We now use line number as defined by ITU-R, period. Compatibility: Add one to the start values. Applications depending on the previous semantics may not function correctly. The restriction "count[0] > 0 and count[1] > 0" has been relaxed to "(count[0] + count[1]) > 0". Rationale: Drivers may allocate resources at scan line granularity and some data services are transmitted only on the first field. The comment that both count values will usually be equal is misleading and pointless and has been removed. This change breaks compatibility with earlier versions: Drivers may return EINVAL, applications may not function correctly. Drivers are again permitted to return negative (unknown) start values as proposed earlier. Why this feature was dropped is unclear. This change may break compatibility with applications depending on the start values being positive. The use of EBUSY and EINVAL error codes with the &VIDIOC-S-FMT; ioctl was clarified. The &EBUSY; was finally documented, and the reserved2 field which was previously mentioned only in the videodev.h header file. New buffer types V4L2_TYPE_VBI_INPUT and V4L2_TYPE_VBI_OUTPUT were added. The former is an alias for the old V4L2_TYPE_VBI, the latter was missing in the videodev.h file.

Added sliced VBI interface proposal.

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. As specified in , drivers must make related device functions available under all minor device numbers. The &func-open; function requires access mode O_RDWR regardless of the device type. All V4L2 drivers exchanging data with applications must support the O_NONBLOCK flag. The O_NOIO flag, a V4L2 symbol which aliased the meaningless O_TRUNC to indicate accesses without data exchange (panel applications) was dropped. Drivers must stay in "panel mode" until the application attempts to initiate a data exchange, see . The &v4l2-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; to the new &VIDIOC-QUERYCAP; ioctl. There are new fields to identify the driver, a new RDS device function V4L2_CAP_RDS_CAPTURE, the V4L2_CAP_AUDIO flag indicates if the device has any audio connectors, another I/O capability V4L2_CAP_ASYNCIO can be flagged. In response to these changes the type field became a bit set and was merged into the flags field. V4L2_FLAG_TUNER was renamed to V4L2_CAP_TUNER, V4L2_CAP_VIDEO_OVERLAY replaced V4L2_FLAG_PREVIEW and V4L2_CAP_VBI_CAPTURE and V4L2_CAP_VBI_OUTPUT replaced V4L2_FLAG_DATA_SERVICE. V4L2_FLAG_READ and V4L2_FLAG_WRITE were merged into V4L2_CAP_READWRITE. The redundant fields inputs, outputs and audios were removed. These properties can be determined as described in and . The somewhat volatile and therefore barely useful fields maxwidth, maxheight, minwidth, minheight, maxframerate were removed. This information is available as described in and . V4L2_FLAG_SELECT was removed. We believe the select() function is important enough to require support of it in all V4L2 drivers exchanging data with applications. The redundant V4L2_FLAG_MONOCHROME flag was removed, this information is available as described in . In &v4l2-input; the assoc_audio field and the capability field and its only flag V4L2_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 &v4l2-output; lost its capability and assoc_audio fields. audioset, modulator and std where added instead. The &v4l2-audio; field audio was renamed to index, for consistency with other structures. A new capability flag V4L2_AUDCAP_STEREO was added to indicated if the audio input in question supports stereo sound. 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.) Again for consistency the &v4l2-audioout; field audio was renamed to index. The &v4l2-tuner; input field was replaced by an index field, permitting devices with multiple tuners. The link between video inputs and tuners is now reversed, inputs point to their tuner. The std substructure became a simple set (more about this below) and moved into &v4l2-input;. A type field was added. Accordingly in &v4l2-modulator; the output was replaced by an index field. In &v4l2-frequency; the port field was replaced by a tuner field containing the respective tuner or modulator index number. A tuner type field was added and the reserved field became larger for future extensions (satellite tuners in particular). 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. Instead of enumerating supported standards with an ioctl applications can now refer to standards by &v4l2-std-id; and symbols defined in the videodev2.h header file. For details see . The &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, if the hardware has this capability. In &v4l2-standard; an index field was added for &VIDIOC-ENUMSTD;. A &v4l2-std-id; field named id was added as machine readable identifier, also replacing the transmission field. The misleading framerate field was renamed to frameperiod. The now obsolete colorstandard information, originally needed to distguish between variations of standards, were removed. Struct v4l2_enumstd ceased to be. &VIDIOC-ENUMSTD; now takes a pointer to a &v4l2-standard; directly. The information which standards are supported by a particular video input or output moved into &v4l2-input; and &v4l2-output; fields named std, respectively. The &v4l2-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 &v4l2-format; the fmt union was extended to contain &v4l2-window;. All image format negotiations are now possible with VIDIOC_G_FMT, VIDIOC_S_FMT and VIDIOC_TRY_FMT; ioctl. The VIDIOC_G_WIN and VIDIOC_S_WIN ioctls to prepare for a video overlay were removed. The type field changed to type &v4l2-buf-type; and the buffer type names changed as follows. Old defines &v4l2-buf-type; V4L2_BUF_TYPE_CAPTURE V4L2_BUF_TYPE_VIDEO_CAPTURE V4L2_BUF_TYPE_CODECIN Omitted for now V4L2_BUF_TYPE_CODECOUT Omitted for now V4L2_BUF_TYPE_EFFECTSIN Omitted for now V4L2_BUF_TYPE_EFFECTSIN2 Omitted for now V4L2_BUF_TYPE_EFFECTSOUT Omitted for now V4L2_BUF_TYPE_VIDEOOUT V4L2_BUF_TYPE_VIDEO_OUTPUT - V4L2_BUF_TYPE_VIDEO_OVERLAY - V4L2_BUF_TYPE_VBI_CAPTURE - V4L2_BUF_TYPE_VBI_OUTPUT - V4L2_BUF_TYPE_SLICED_VBI_CAPTURE - V4L2_BUF_TYPE_SLICED_VBI_OUTPUT V4L2_BUF_TYPE_PRIVATE_BASE V4L2_BUF_TYPE_PRIVATE In &v4l2-fmtdesc; a &v4l2-buf-type; field named type was added as in &v4l2-format;. The VIDIOC_ENUM_FBUFFMT 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 &v4l2-pix-format; the depth field was removed, assuming applications which recognize the format by its four-character-code already know the color depth, and others do not care about it. The same rationale lead to the removal of the V4L2_FMT_FLAG_COMPRESSED flag. The V4L2_FMT_FLAG_SWCONVECOMPRESSED flag was removed because drivers are not supposed to convert images in kernel space. A user library of conversion functions should be provided instead. The V4L2_FMT_FLAG_BYTESPERLINE flag was redundant. Applications can set the bytesperline field to zero to get a reasonable default. Since the remaining flags were replaced as well, the flags field itself was removed. The interlace flags were replaced by a &v4l2-field; value in a newly added field field. Old flag &v4l2-field; V4L2_FMT_FLAG_NOT_INTERLACED ? V4L2_FMT_FLAG_INTERLACED = V4L2_FMT_FLAG_COMBINED V4L2_FIELD_INTERLACED V4L2_FMT_FLAG_TOPFIELD = V4L2_FMT_FLAG_ODDFIELD V4L2_FIELD_TOP V4L2_FMT_FLAG_BOTFIELD = V4L2_FMT_FLAG_EVENFIELD V4L2_FIELD_BOTTOM - V4L2_FIELD_SEQ_TB - V4L2_FIELD_SEQ_BT - V4L2_FIELD_ALTERNATE The color space flags were replaced by a &v4l2-colorspace; value in a newly added colorspace field, where one of V4L2_COLORSPACE_SMPTE170M, V4L2_COLORSPACE_BT878, V4L2_COLORSPACE_470_SYSTEM_M or V4L2_COLORSPACE_470_SYSTEM_BG replaces V4L2_FMT_CS_601YUV. In &v4l2-requestbuffers; the type field was properly defined as &v4l2-buf-type;. Buffer types changed as mentioned above. A new memory field of type &v4l2-memory; was added to distinguish between I/O methods using buffers allocated by the driver or the application. See for details. In &v4l2-buffer; the type field was properly defined as &v4l2-buf-type;. Buffer types changed as mentioned above. A field field of type &v4l2-field; was added to indicate if a buffer contains a top or bottom field. The old field flags were removed. Since no unadjusted system time clock was added to the