# Changes

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.

# Differences between V4L 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, 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.

## Opening and Closing Devices

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.

### V4L Device Types, Names and Numbers

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;.

## Querying Capabilities

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.

## Video Sources

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.

## Tuning

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.

## Image Properties

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.

## Audio

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 .

## 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 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;.

## Cropping

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.

## Reading Images, Memory Mapping

### Capturing using the read method

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 .

### Capturing using memory mapping

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 .

## Reading Raw VBI Data

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, 16 Old 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.

## 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 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 .

# Changes of the V4L2 API

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.

## Early Versions

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.

## V4L2 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 v4l2_buffer as a parameter. Added digital zoom (cropping) controls.

## V4L2 Version 0.18 1999-03-16

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.

## V4L2 Version 0.19 1999-06-05

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.

## V4L2 Version 0.20 (1999-09-10)

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.

1. Some typos in `V4L2_FMT_FLAG` symbols were fixed. &v4l2-clip; was changed for compatibility with v4l. (1999-08-30)

2. `V4L2_TUNER_SUB_LANG1` was added. (1999-09-05)

3. 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);

4. 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.

5. 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.

6. 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.

7. 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.

8. 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.

## V4L2 Version 0.20 incremental changes

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".

## V4L2 Version 0.20 2000-11-23

A number of changes were made to the raw VBI interface.

1. 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.

2. 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.

3. 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.

4. 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.

## V4L2 Version 0.20 2002-07-25

Added sliced VBI interface proposal.

## 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 , drivers must make related device functions available under all minor device numbers.

2. 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 .

3. 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 .

4. 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.

5. 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.

6. 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).

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. 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.

8. The &v4l2-queryctrl; fields category and group did not catch on and/or were not implemented as expected and therefore removed.

9. 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`

10. 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`.

11. 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`.

12. 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.

13. 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 kernel as planned, the timestamp field changed back from type stamp_t, an unsigned 64 bit integer expressing the sample time in nanoseconds, to struct timeval. With the addition of a second memory mapping method the offset field moved into union m, and a new memory field of type &v4l2-memory; was added to distinguish between I/O methods. See for details.

    The `V4L2_BUF_REQ_CONTIG` flag was used by the V4L compatibility layer, after changes to this code it was no longer needed. The `V4L2_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 was removed.

14. In &v4l2-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 `V4L2_FBUF_CAP_LIST_CLIPPING` and `V4L2_FBUF_CAP_BITMAP_CLIPPING`.

15. In &v4l2-clip; the x, y, width and height field moved into a c substructure of type &v4l2-rect;. The x and y fields were renamed to left and top, &ie; offsets to a context dependent origin.

16. In &v4l2-window; the x, y, width and height field moved into a w substructure as above. A field field of type %v4l2-field; was added to distinguish between field and frame (interlaced) overlay.

17. The digital zoom interface, including struct v4l2_zoomcap, struct v4l2_zoom, `V4L2_ZOOM_NONCAP` and `V4L2_ZOOM_WHILESTREAMING` was replaced by a new cropping and scaling interface. The previously unused struct v4l2_cropcap and v4l2_crop where redefined for this purpose. See for details.

18. In &v4l2-vbi-format; the SAMPLE_FORMAT field now contains a four-character-code as used to identify video image formats and `V4L2_PIX_FMT_GREY` replaces the `V4L2_VBI_SF_UBYTE` define. The reserved field was extended.

19. In &v4l2-captureparm; the type of the timeperframe field changed from unsigned long to &v4l2-fract;. This allows the accurate expression of multiples of the NTSC-M frame rate 30000 / 1001. A new field readbuffers was added to control the driver behaviour in read I/O mode.

    Similar changes were made to &v4l2-outputparm;.

20. The struct v4l2_performance and `VIDIOC_G_PERF` ioctl were dropped. Except when using the read/write I/O method, which is limited anyway, this information is already available to applications.

21. The example transformation from RGB to YCbCr color space in the old V4L2 documentation was inaccurate, this has been corrected in .

## 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 solely by having exactly one tuner whose type field reads `V4L2_TUNER_RADIO`.

2. An optional driver access priority mechanism was added, see 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 inputs. 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 was removed on Kernel 2.6.39. The &VIDIOC-ENUMAUDIO; 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 between the old and new ioctls, but drivers and applications must be updated to successfully compile again.

4. The &VIDIOC-OVERLAY; ioctl was incorrectly defined with write-read parameter. It was changed to write-only, while the write-read version was renamed to `VIDIOC_OVERLAY_OLD`. The old ioctl was removed on Kernel 2.6.39. Until further the "videodev" kernel module will automatically translate to the new version, so drivers must be recompiled, but not applications.

5. 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; ioctls were defined with write-only parameter, inconsistent with other ioctls modifying their argument. They were changed to write-read, while a `_OLD` suffix was added to the write-only versions. The old ioctls were removed on Kernel 2.6.39. Drivers and applications assuming a constant parameter need an update.

## V4L2 2003-11-05

1. In the following pixel formats were incorrectly transferred from Bill Dirks' V4L2 specification. Descriptions below refer to bytes in memory, in ascending address order.

   Symbol | In this document prior to revision 0.5 | Corrected
   --- | --- | ---
   `V4L2_PIX_FMT_RGB24` | B, G, R | R, G, B
   `V4L2_PIX_FMT_BGR24` | R, G, B | B, G, R
   `V4L2_PIX_FMT_RGB32` | B, 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 the mapping of the V4L `VIDEO_PALETTE_RGB24` and `VIDEO_PALETTE_RGB32` formats to V4L2 pixel formats was accordingly corrected.

2. 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 .

## V4L2 in Linux 2.6.6, 2004-05-09

1. The &VIDIOC-CROPCAP; ioctl was incorrectly defined with read-only parameter. It is now defined as write-read ioctl, while the read-only version was renamed to `VIDIOC_CROPCAP_OLD`. The old ioctl was removed on Kernel 2.6.39.

## V4L2 in Linux 2.6.8

1. A new field input (former reserved[0]) was added to the &v4l2-buffer; structure. Purpose of this field is to alternate between video inputs (&eg; cameras) in step with the video capturing process. This function must be enabled with the new `V4L2_BUF_FLAG_INPUT` flag. The flags field is no longer read-only.

## V4L2 spec erratum 2004-08-01

1. The return value of the function was incorrectly documented.

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 documentation of the &VIDIOC-QBUF; and &VIDIOC-DQBUF; ioctls did not mention the &v4l2-buffer; memory field. It was also missing from examples. Also on the `VIDIOC_DQBUF` page the &EIO; was not documented.

## V4L2 in Linux 2.6.14

1. A new sliced VBI interface was added. It is documented in and replaces the interface first proposed in V4L2 specification 0.8.

## V4L2 in Linux 2.6.15

1. The &VIDIOC-LOG-STATUS; ioctl was added.

2. New video standards `V4L2_STD_NTSC_443`, `V4L2_STD_SECAM_LC`, `V4L2_STD_SECAM_DK` (a set of SECAM D, K and K1), and `V4L2_STD_ATSC` (a set of `V4L2_STD_ATSC_8_VSB` and `V4L2_STD_ATSC_16_VSB`) were defined. Note the `V4L2_STD_525_60` set now includes `V4L2_STD_NTSC_443`. See also .

3. The `VIDIOC_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 v4l2_mpeg_compression pointer. (The `VIDIOC_G_MPEGCOMP` and `VIDIOC_S_MPEGCOMP` ioctls where removed in Linux 2.6.25.)

## V4L2 spec erratum 2005-11-27

The capture example in called the &VIDIOC-S-CROP; ioctl without checking if cropping is supported. In the video standard selection example in the &VIDIOC-S-STD; call used the wrong argument type.

## V4L2 spec erratum 2006-01-10

1. The `V4L2_IN_ST_COLOR_KILL` flag in &v4l2-input; not only indicates if the color killer is enabled, but also if it is active. (The color killer disables color decoding when it detects no color in the video signal to improve the image quality.)

2. &VIDIOC-S-PARM; is a write-read ioctl, not write-only as stated on its reference page. The ioctl changed in 2003 as noted above.

## V4L2 spec erratum 2006-02-03

1. In &v4l2-captureparm; and &v4l2-outputparm; the timeperframe field gives the time in seconds, not microseconds.

## V4L2 spec erratum 2006-02-04

1. The clips field in &v4l2-window; must point to an array of &v4l2-clip;, not a linked list, because drivers ignore the struct v4l2_clip.next pointer.

## V4L2 in Linux 2.6.17

1. New video standard macros were added: `V4L2_STD_NTSC_M_KR` (NTSC M South Korea), and the sets `V4L2_STD_MN`, `V4L2_STD_B`, `V4L2_STD_GH` and `V4L2_STD_DK`. The `V4L2_STD_NTSC` and `V4L2_STD_SECAM` sets now include `V4L2_STD_NTSC_M_KR` and `V4L2_STD_SECAM_LC` respectively.

2. A new `V4L2_TUNER_MODE_LANG1_LANG2` was defined to record both languages of a bilingual program. The use of `V4L2_TUNER_MODE_STEREO` for this purpose is deprecated now. See the &VIDIOC-G-TUNER; section for details.

## V4L2 spec erratum 2006-09-23 (Draft 0.15)

1. In various places `V4L2_BUF_TYPE_SLICED_VBI_CAPTURE` and `V4L2_BUF_TYPE_SLICED_VBI_OUTPUT` of the sliced VBI interface were not mentioned along with other buffer types.

2. In it was clarified that the &v4l2-audio; mode field is a flags field.

3. did not mention the sliced VBI and radio capability flags.

4. In it was clarified that applications must initialize the tuner type field of &v4l2-frequency; before calling &VIDIOC-S-FREQUENCY;.

5. The reserved array in &v4l2-requestbuffers; has 2 elements, not 32.

6. In and the device file names `/dev/vout` which never caught on were replaced by `/dev/video`.

7. With Linux 2.6.15 the possible range for VBI device minor numbers was extended from 224-239 to 224-255. Accordingly device file names `/dev/vbi0` to `/dev/vbi31` are possible now.

## V4L2 in Linux 2.6.18

1. New ioctls &VIDIOC-G-EXT-CTRLS;, &VIDIOC-S-EXT-CTRLS; and &VIDIOC-TRY-EXT-CTRLS; were added, a flag to skip unsupported controls with &VIDIOC-QUERYCTRL;, new control types `V4L2_CTRL_TYPE_INTEGER64` and `V4L2_CTRL_TYPE_CTRL_CLASS` (), and new control flags `V4L2_CTRL_FLAG_READ_ONLY`, `V4L2_CTRL_FLAG_UPDATE`, `V4L2_CTRL_FLAG_INACTIVE` and `V4L2_CTRL_FLAG_SLIDER` (). See for details.

## V4L2 in Linux 2.6.19

1. In &v4l2-sliced-vbi-cap; a buffer type field was added replacing a reserved field. Note on architectures where the size of enum types differs from int types the size of the structure changed. The &VIDIOC-G-SLICED-VBI-CAP; ioctl was redefined from being read-only to write-read. Applications must initialize the type field and clear the reserved fields now. These changes may break the compatibility with older drivers and applications.

2. The ioctls &VIDIOC-ENUM-FRAMESIZES; and &VIDIOC-ENUM-FRAMEINTERVALS; were added.

3. A new pixel format `V4L2_PIX_FMT_RGB444` () was added.

## V4L2 spec erratum 2006-10-12 (Draft 0.17)

1. `V4L2_PIX_FMT_HM12` () is a YUV 4:2:0, not 4:2:2 format.

## V4L2 in Linux 2.6.21

1. The `videodev2.h` header file is now dual licensed under GNU General Public License version two or later, and under a 3-clause BSD-style license.

## V4L2 in Linux 2.6.22

1. Two new field orders `V4L2_FIELD_INTERLACED_TB` and `V4L2_FIELD_INTERLACED_BT` were added. See for details.

2. Three new clipping/blending methods with a global or straight or inverted local alpha value were added to the video overlay interface. See the description of the &VIDIOC-G-FBUF; and &VIDIOC-S-FBUF; ioctls for details.

   A new global_alpha field was added to v4l2_window, extending the structure. This may break compatibility with applications using a struct v4l2_window directly. However the VIDIOC_G/S/TRY_FMT ioctls, which take a pointer to a v4l2_format parent structure with padding bytes at the end, are not affected.

3. The format of the chromakey field in &v4l2-window; changed from "host order RGB32" to a pixel value in the same format as the framebuffer. This may break compatibility with existing applications. Drivers supporting the "host order RGB32" format are not known.

## V4L2 in Linux 2.6.24

1. The pixel formats `V4L2_PIX_FMT_PAL8`, `V4L2_PIX_FMT_YUV444`, `V4L2_PIX_FMT_YUV555`, `V4L2_PIX_FMT_YUV565` and `V4L2_PIX_FMT_YUV32` were added.

## V4L2 in Linux 2.6.25

1. The pixel formats `V4L2_PIX_FMT_Y16` and `V4L2_PIX_FMT_SBGGR16` were added.

2. New controls `V4L2_CID_POWER_LINE_FREQUENCY`, `V4L2_CID_HUE_AUTO`, `V4L2_CID_WHITE_BALANCE_TEMPERATURE`, `V4L2_CID_SHARPNESS` and `V4L2_CID_BACKLIGHT_COMPENSATION` were added. The controls `V4L2_CID_BLACK_LEVEL`, `V4L2_CID_WHITENESS`, `V4L2_CID_HCENTER` and `V4L2_CID_VCENTER` were deprecated.

3. A Camera controls class was added, with the new controls `V4L2_CID_EXPOSURE_AUTO`, `V4L2_CID_EXPOSURE_ABSOLUTE`, `V4L2_CID_EXPOSURE_AUTO_PRIORITY`, `V4L2_CID_PAN_RELATIVE`, `V4L2_CID_TILT_RELATIVE`, `V4L2_CID_PAN_RESET`, `V4L2_CID_TILT_RESET`, `V4L2_CID_PAN_ABSOLUTE`, `V4L2_CID_TILT_ABSOLUTE`, `V4L2_CID_FOCUS_ABSOLUTE`, `V4L2_CID_FOCUS_RELATIVE` and `V4L2_CID_FOCUS_AUTO`.

4. The `VIDIOC_G_MPEGCOMP` and `VIDIOC_S_MPEGCOMP` ioctls, which were superseded by the extended controls interface in Linux 2.6.18, where finally removed from the `videodev2.h` header file.

## V4L2 in Linux 2.6.26

1. The pixel formats `V4L2_PIX_FMT_Y16` and `V4L2_PIX_FMT_SBGGR16` were added.

2. Added user controls `V4L2_CID_CHROMA_AGC` and `V4L2_CID_COLOR_KILLER`.

## V4L2 in Linux 2.6.27

1. The &VIDIOC-S-HW-FREQ-SEEK; ioctl and the `V4L2_CAP_HW_FREQ_SEEK` capability were added.

2. The pixel formats `V4L2_PIX_FMT_YVYU`, `V4L2_PIX_FMT_PCA501`, `V4L2_PIX_FMT_PCA505`, `V4L2_PIX_FMT_PCA508`, `V4L2_PIX_FMT_PCA561`, `V4L2_PIX_FMT_SGBRG8`, `V4L2_PIX_FMT_PAC207` and `V4L2_PIX_FMT_PJPG` were added.

## V4L2 in Linux 2.6.28

1. Added `V4L2_MPEG_AUDIO_ENCODING_AAC` and `V4L2_MPEG_AUDIO_ENCODING_AC3` MPEG audio encodings.

2. Added `V4L2_MPEG_VIDEO_ENCODING_MPEG_4_AVC` MPEG video encoding.

3. The pixel formats `V4L2_PIX_FMT_SGRBG10` and `V4L2_PIX_FMT_SGRBG10DPCM8` were added.

## V4L2 in Linux 2.6.29

1. The `VIDIOC_G_CHIP_IDENT` ioctl was renamed to `VIDIOC_G_CHIP_IDENT_OLD` and &VIDIOC-DBG-G-CHIP-IDENT; was introduced in its place. The old struct v4l2_chip_ident was renamed to v4l2_chip_ident_old.

2. The pixel formats `V4L2_PIX_FMT_VYUY`, `V4L2_PIX_FMT_NV16` and `V4L2_PIX_FMT_NV61` were added.

3. Added camera controls `V4L2_CID_ZOOM_ABSOLUTE`, `V4L2_CID_ZOOM_RELATIVE`, `V4L2_CID_ZOOM_CONTINUOUS` and `V4L2_CID_PRIVACY`.

## V4L2 in Linux 2.6.30

1. New control flag `V4L2_CTRL_FLAG_WRITE_ONLY` was added.

2. New control `V4L2_CID_COLORFX` was added.

## V4L2 in Linux 2.6.32

1. In order to be easier to compare a V4L2 API and a kernel version, now V4L2 API is numbered using the Linux Kernel version numeration.

2. Finalized the RDS capture API. See for more information.

3. Added new capabilities for modulators and RDS encoders.

4. Add description for libv4l API.

5. Added support for string controls via new type `V4L2_CTRL_TYPE_STRING`.

6. Added `V4L2_CID_BAND_STOP_FILTER` documentation.

7. Added FM Modulator (FM TX) Extended Control Class: `V4L2_CTRL_CLASS_FM_TX` and their Control IDs.

8. Added Remote Controller chapter, describing the default Remote Controller mapping for media devices.

## V4L2 in Linux 2.6.33

1. Added support for Digital Video timings in order to support HDTV receivers and transmitters.

## V4L2 in Linux 2.6.34

1. Added `V4L2_CID_IRIS_ABSOLUTE` and `V4L2_CID_IRIS_RELATIVE` controls to the Camera controls class.

## V4L2 in Linux 2.6.37

1. Remove the vtx (videotext/teletext) API. This API was no longer used and no hardware exists to verify the API. Nor were any userspace applications found that used it. It was originally scheduled for removal in 2.6.35.

## V4L2 in Linux 2.6.39

1. The old VIDIOC_*_OLD symbols and V4L1 support were removed.

2. Multi-planar API added. Does not affect the compatibility of current drivers and applications. See multi-planar API for details.

## V4L2 in Linux 3.1

1. VIDIOC_QUERYCAP now returns a per-subsystem version instead of a per-driver one.

   Standardize an error code for invalid ioctl.

   Added V4L2_CTRL_TYPE_BITMASK.

## V4L2 in Linux 3.2

1. V4L2_CTRL_FLAG_VOLATILE was added to signal volatile controls to userspace.

2. Add selection API for extended control over cropping and composing. Does not affect the compatibility of current drivers and applications. See selection API for details.

## V4L2 in Linux 3.3

1. Added `V4L2_CID_ALPHA_COMPONENT` control to the User controls class.

2. Added the device_caps field to struct v4l2_capabilities and added the new V4L2_CAP_DEVICE_CAPS capability.

## V4L2 in Linux 3.4

1. Added JPEG compression control class.

## Relation of V4L2 to other Linux multimedia APIs

### 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 This is not implemented in XFree86. . 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 V4L2 video overlay interface. The driver can easily determine the overlay target, &ie; visible graphics memory or off-screen buffers for a destructive overlay. It can program the RAMDAC for a non-destructive overlay, scaling or color-keying, or the clipping functions of the video capture hardware, always in sync with drawing operations or windows moving or changing their stacking order.

To combine the advantages of Xv and V4L a special Xv driver exists in XFree86 and XOrg, just programming any overlay capable Video4Linux device it finds. To enable it `/etc/X11/XF86Config` must contain these lines:

    Section "Module"
        Load "v4l"
    EndSection

As of XFree86 4.2 this driver still supports only V4L 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 are discussed in 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 API is useful to display images captured with V4L2 devices.

### Digital Video

V4L2 does not support digital terrestrial, cable or satellite broadcast. A separate project aiming at digital receivers exists. You can find its homepage at http://linuxtv.org. The Linux DVB API has no connection to the V4L2 API except that drivers for hybrid hardware may support both.

### Audio Interfaces

[to do - OSS/ALSA]

## Experimental API Elements

The following V4L2 API elements are currently experimental and may change in the future.

- Video Output Overlay (OSD) Interface, .

- `V4L2_BUF_TYPE_VIDEO_OUTPUT_OVERLAY`, &v4l2-buf-type;, .

- `V4L2_CAP_VIDEO_OUTPUT_OVERLAY`, &VIDIOC-QUERYCAP; ioctl, .

- &VIDIOC-ENUM-FRAMESIZES; and &VIDIOC-ENUM-FRAMEINTERVALS; ioctls.

- &VIDIOC-G-ENC-INDEX; ioctl.

- &VIDIOC-ENCODER-CMD; and &VIDIOC-TRY-ENCODER-CMD; ioctls.

- &VIDIOC-DBG-G-REGISTER; and &VIDIOC-DBG-S-REGISTER; ioctls.

- &VIDIOC-DBG-G-CHIP-IDENT; ioctl.

- Flash API.

- &VIDIOC-CREATE-BUFS; and &VIDIOC-PREPARE-BUF; ioctls.

- Selection API.

## Obsolete API Elements

The following V4L2 API elements were superseded by new interfaces and should not be implemented in new drivers.

- `VIDIOC_G_MPEGCOMP` and `VIDIOC_S_MPEGCOMP` ioctls. Use Extended Controls, .