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.. Permission is granted to copy, distribute and/or modify this
.. document under the terms of the GNU Free Documentation License,
.. Version 1.1 or any later version published by the Free Software
.. Foundation, with no Invariant Sections, no Front-Cover Texts
.. and no Back-Cover Texts. A copy of the license is included at
.. Documentation/media/uapi/fdl-appendix.rst.
.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections
.. _hist-v4l2:
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 :ref:`select() <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`` :ref:`open() <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
1998-10-02: The ``id`` field was removed from struct
struct ``video_standard`` and the color subcarrier fields were
renamed. The :ref:`VIDIOC_QUERYSTD` ioctl was
renamed to :ref:`VIDIOC_ENUMSTD`,
:ref:`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 struct :c:type:`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
:ref:`VIDIOC_S_CTRL <VIDIOC_G_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
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. struct
:c:type:`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,
.. code-block:: c
err = ioctl (fd, VIDIOC_XXX, V4L2_XXX);
.. code-block:: c
int a = V4L2_XXX; err = ioctl(fd, VIDIOC_XXX, &a);
4. All the different get- and set-format commands were swept into one
:ref:`VIDIOC_S_FMT <VIDIOC_G_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_S_VBIFMT`` and ``VIDIOC_G_VBIFMT``. The image format
structure struct :c:type:`v4l2_format` was renamed to struct
:c:type:`v4l2_pix_format`, while struct
:c:type:`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 struct
:c:type:`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
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 struct :c:type:`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\*/
/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 struct
:c:type:`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 struct :c:type:`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
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
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
:ref:`VIDIOC_S_FREQUENCY <VIDIOC_G_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 :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` and
:ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctls may fail now if the struct
struct ``v4l2_fmt`` ``type`` field does not contain
``V4L2_BUF_TYPE_VBI``. In the documentation of the struct
:c:type:`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 :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl was
clarified. The ``EBUSY`` error code 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 :ref:`related`, drivers must make related device
functions available under all minor device numbers.
2. The :ref:`open() <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 struct :c:type:`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`` error code to the new
:ref:`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_READ`` and ``V4L2_FLAG_WRITE`` were merged into
The redundant fields ``inputs``, ``outputs`` and ``audios`` were
removed. These properties can be determined as described in
:ref:`video` and :ref:`audio`.
The somewhat volatile and therefore barely useful fields
``maxwidth``, ``maxheight``, ``minwidth``, ``minheight``,
``maxframerate`` were removed. This information is available as
described in :ref:`format` and :ref:`standard`.
``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 :ref:`format`.
4. In struct :c:type:`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 struct :c:type:`v4l2_output` lost its
``capability`` and ``assoc_audio`` fields. ``audioset``,
``modulator`` and ``std`` where added instead.
5. The struct :c:type:`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 struct
:c:type:`v4l2_audioout` field ``audio`` was renamed
to ``index``.
6. The struct :c:type:`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 struct
:c:type:`v4l2_input`. A ``type`` field was added.
Accordingly in struct :c:type:`v4l2_modulator` the
``output`` was replaced by an ``index`` field.
In struct :c:type:`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 :ref:`v4l2_std_id <v4l2-std-id>` and symbols
defined in the ``videodev2.h`` header file. For details see
:ref:`standard`. The :ref:`VIDIOC_G_STD <VIDIOC_G_STD>` and
:ref:`VIDIOC_S_STD <VIDIOC_G_STD>` now take a pointer to this
type as argument. :ref:`VIDIOC_QUERYSTD` was
added to autodetect the received standard, if the hardware has this
capability. In struct :c:type:`v4l2_standard` an
``index`` field was added for
:ref:`v4l2_std_id <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
Struct ``v4l2_enumstd`` ceased to be.
:ref:`VIDIOC_ENUMSTD` now takes a pointer to a
struct :c:type:`v4l2_standard` directly. The
information which standards are supported by a particular video
input or output moved into struct :c:type:`v4l2_input`
and struct :c:type:`v4l2_output` fields named ``std``,
8. The struct :ref:`v4l2_queryctrl <v4l2-queryctrl>` fields
``category`` and ``group`` did not catch on and/or were not
implemented as expected and therefore removed.
9. The :ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` ioctl was added to
negotiate data formats as with
:ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`, but without the overhead of
programming the hardware and regardless of I/O in progress.
In struct :c:type:`v4l2_format` the ``fmt`` union was
extended to contain struct :c:type:`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 enum
:c:type:`v4l2_buf_type` and the buffer type names
changed as follows.
.. flat-table::
:header-rows: 1
:stub-columns: 0
* - Old defines
- enum :c:type:`v4l2_buf_type`
- Omitted for now
- Omitted for now
- Omitted for now
- Omitted for now
- Omitted for now
* - ``-``
* - ``-``
* - ``-``
* - ``-``
* - ``-``
- ``V4L2_BUF_TYPE_PRIVATE`` (but this is deprecated)
10. In struct :c:type:`v4l2_fmtdesc` a enum
:c:type:`v4l2_buf_type` field named ``type`` was
added as in struct :c:type:`v4l2_format`. The
``VIDIOC_ENUM_FBUFFMT`` ioctl is no longer needed and was removed.
These calls can be replaced by
:ref:`VIDIOC_ENUM_FMT` with type
11. In struct :c:type:`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_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 enum
:c:type:`v4l2_field` value in a newly added ``field``
.. flat-table::
:header-rows: 1
:stub-columns: 0
* - Old flag
- enum :c:type:`v4l2_field`
- ?
- ``V4L2_FIELD_TOP``
* - ``-``
* - ``-``
* - ``-``
The color space flags were replaced by a enum
:c:type:`v4l2_colorspace` value in a newly added
``colorspace`` field, where one of ``V4L2_COLORSPACE_SMPTE170M``,
``V4L2_COLORSPACE_470_SYSTEM_BG`` replaces ``V4L2_FMT_CS_601YUV``.
12. In struct :c:type:`v4l2_requestbuffers` the
``type`` field was properly defined as enum
:c:type:`v4l2_buf_type`. Buffer types changed as
mentioned above. A new ``memory`` field of type enum
:c:type:`v4l2_memory` was added to distinguish between
I/O methods using buffers allocated by the driver or the
application. See :ref:`io` for details.
13. In struct :c:type:`v4l2_buffer` the ``type`` field was
properly defined as enum :c:type:`v4l2_buf_type`.
Buffer types changed as mentioned above. A ``field`` field of type
enum :c: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 :c:type:`timeval`. With the addition
of a second memory mapping method the ``offset`` field moved into
union ``m``, and a new ``memory`` field of type enum
:c:type:`v4l2_memory` was added to distinguish between
I/O methods. See :ref:`io` 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 struct :c:type:`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
15. In struct :c:type:`v4l2_clip` the ``x``, ``y``,
``width`` and ``height`` field moved into a ``c`` substructure of
type struct :c:type:`v4l2_rect`. The ``x`` and ``y``
fields were renamed to ``left`` and ``top``, i. e. offsets to a
context dependent origin.
16. In struct :c:type:`v4l2_window` the ``x``, ``y``,
``width`` and ``height`` field moved into a ``w`` substructure as
above. A ``field`` field of type :c:type:`v4l2_field` was added to
distinguish between field and frame (interlaced) overlay.
17. The digital zoom interface, including struct
struct ``v4l2_zoomcap``, struct
struct ``v4l2_zoom``, ``V4L2_ZOOM_NONCAP`` and
``V4L2_ZOOM_WHILESTREAMING`` was replaced by a new cropping and
scaling interface. The previously unused struct
struct :c:type:`v4l2_cropcap` and struct :c:type:`v4l2_crop`
where redefined for this purpose. See :ref:`crop` for details.
18. In struct :c:type:`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
19. In struct :c:type:`v4l2_captureparm` the type of
the ``timeperframe`` field changed from unsigned long to struct
:c:type:`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 struct
20. The struct ``v4l2_performance`` and
``VIDIOC_G_PERF`` ioctl were dropped. Except when using the
:ref:`read/write I/O method <rw>`, 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
:ref:`app-pri` for details.
3. The audio input and output interface was found to be incomplete.
Previously the :ref:`VIDIOC_G_AUDIO <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
:ref:`VIDIOC_ENUMAUDIO` ioctl was added to
enumerate audio inputs, while
:ref:`VIDIOC_G_AUDIO <VIDIOC_G_AUDIO>` now reports the current
audio input.
The same changes were made to
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 :ref:`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. :ref:`overlay` 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 :ref:`VIDIOC_S_PARM <VIDIOC_G_PARM>` and
:ref:`VIDIOC_S_CTRL <VIDIOC_G_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 :ref:`pixfmt-rgb` the following pixel formats were incorrectly
transferred from Bill Dirks' V4L2 specification. Descriptions below
refer to bytes in memory, in ascending address order.
.. flat-table::
:header-rows: 1
:stub-columns: 0
* - 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 :ref:`v4l-image-properties` 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 :ref:`pixfmt-rgb`.
V4L2 in Linux 2.6.6, 2004-05-09
1. The :ref:`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
struct :c:type:`v4l2_buffer` structure. Purpose of this
field is to alternate between video inputs (e. g. 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 :ref:`func-open` function was incorrectly
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 :ref:`VIDIOC_QBUF` and
:ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctls did not mention the
struct :c:type:`v4l2_buffer` ``memory`` field. It was
also missing from examples. Also on the ``VIDIOC_DQBUF`` page the ``EIO``
error code was not documented.
V4L2 in Linux 2.6.14
1. A new sliced VBI interface was added. It is documented in
:ref:`sliced` and replaces the interface first proposed in V4L2
specification 0.8.
V4L2 in Linux 2.6.15
1. The :ref:`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 :ref:`capture-example` called the
:ref:`VIDIOC_S_CROP <VIDIOC_G_CROP>` ioctl without checking if
cropping is supported. In the video standard selection example in
:ref:`standard` the :ref:`VIDIOC_S_STD <VIDIOC_G_STD>` call used
the wrong argument type.
V4L2 spec erratum 2006-01-10
1. The ``V4L2_IN_ST_COLOR_KILL`` flag in struct
:c:type:`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. :ref:`VIDIOC_S_PARM <VIDIOC_G_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 struct :c:type:`v4l2_captureparm` and struct
:c:type:`v4l2_outputparm` the ``timeperframe``
field gives the time in seconds, not microseconds.
V4L2 spec erratum 2006-02-04
1. The ``clips`` field in struct :c:type:`v4l2_window`
must point to an array of struct :c:type:`v4l2_clip`, not
a linked list, because drivers ignore the struct
struct :c:type:`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 :ref:`VIDIOC_G_TUNER <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 :ref:`VIDIOC_G_AUDIO <VIDIOC_G_AUDIO>` it was clarified that the struct
:c:type:`v4l2_audio` ``mode`` field is a flags field.
3. :ref:`VIDIOC_QUERYCAP` did not mention the sliced VBI and radio
capability flags.
4. In :ref:`VIDIOC_G_FREQUENCY <VIDIOC_G_FREQUENCY>` it was clarified that applications
must initialize the tuner ``type`` field of struct
:c:type:`v4l2_frequency` before calling
5. The ``reserved`` array in struct
:c:type:`v4l2_requestbuffers` has 2 elements,
not 32.
6. In :ref:`output` and :ref:`raw-vbi` 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
flag to skip unsupported controls with
:ref:`VIDIOC_QUERYCTRL`, new control types
(:c:type:`v4l2_ctrl_type`), and new control flags
(:ref:`control-flags`). See :ref:`extended-controls` for details.
V4L2 in Linux 2.6.19
1. In struct :c:type:`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
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
2. The ioctls :ref:`VIDIOC_ENUM_FRAMESIZES`
were added.
3. A new pixel format ``V4L2_PIX_FMT_RGB444`` (:ref:`pixfmt-rgb`) was
V4L2 spec erratum 2006-10-12 (Draft 0.17)
1. ``V4L2_PIX_FMT_HM12`` (:ref:`reserved-formats`) 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 :c:type:`v4l2_field` for
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 :ref:`VIDIOC_G_FBUF <VIDIOC_G_FBUF>`
and :ref:`VIDIOC_S_FBUF <VIDIOC_G_FBUF>` ioctls for details.
A new ``global_alpha`` field was added to
:c:type:`v4l2_window`, extending the structure. This
may *break compatibility* with applications using a struct
struct :c:type:`v4l2_window` directly. However the
:ref:`VIDIOC_G/S/TRY_FMT <VIDIOC_G_FMT>` ioctls, which take a
pointer to a :c:type:`v4l2_format` parent structure
with padding bytes at the end, are not affected.
3. The format of the ``chromakey`` field in struct
:c:type:`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 :ref:`V4L2_PIX_FMT_Y16 <V4L2-PIX-FMT-Y16>` and
:ref:`V4L2_PIX_FMT_SBGGR16 <V4L2-PIX-FMT-SBGGR16>` were added.
2. New :ref:`controls <control>` ``V4L2_CID_POWER_LINE_FREQUENCY``,
added. The controls ``V4L2_CID_BLACK_LEVEL``, ``V4L2_CID_WHITENESS``,
``V4L2_CID_HCENTER`` and ``V4L2_CID_VCENTER`` were deprecated.
3. A :ref:`Camera controls class <camera-controls>` was added, with
the new controls ``V4L2_CID_EXPOSURE_AUTO``,
4. The ``VIDIOC_G_MPEGCOMP`` and ``VIDIOC_S_MPEGCOMP`` ioctls, which
were superseded by the :ref:`extended controls <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 in Linux 2.6.27
1. The :ref:`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
``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
introduced in its place. The old struct
struct ``v4l2_chip_ident`` was renamed to
struct ``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 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 :ref:`rds` 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
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 FM Receiver (FM RX) Extended Control Class:
``V4L2_CTRL_CLASS_FM_RX`` and their Control IDs.
9. 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
controls to the :ref:`Camera controls class <camera-controls>`.
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 :ref:`multi-planar API <planar-apis>`
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.
V4L2 in Linux 3.2
1. V4L2_CTRL_FLAG_VOLATILE was added to signal volatile controls to
2. Add selection API for extended control over cropping and composing.
Does not affect the compatibility of current drivers and
applications. See :ref:`selection API <selection-api>` for details.
V4L2 in Linux 3.3
1. Added ``V4L2_CID_ALPHA_COMPONENT`` control to the
:ref:`User controls class <control>`.
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 :ref:`JPEG compression control class <jpeg-controls>`.
2. Extended the DV Timings API:
V4L2 in Linux 3.5
1. Added integer menus, the new type will be
2. Added selection API for V4L2 subdev interface:
``V4L2_COLORFX_ARBITRARY_CBCR`` menu items to the
``V4L2_CID_COLORFX`` control.
4. Added ``V4L2_CID_COLORFX_CBCR`` control.
5. Added camera controls ``V4L2_CID_AUTO_EXPOSURE_BIAS``,
V4L2 in Linux 3.6
1. Replaced ``input`` in struct :c:type:`v4l2_buffer` by
``reserved2`` and removed ``V4L2_BUF_FLAG_INPUT``.
3. Added support for frequency band enumerations:
V4L2 in Linux 3.9
1. Added timestamp types to ``flags`` field in
struct :c:type:`v4l2_buffer`. See :ref:`buffer-flags`.
2. Added ``V4L2_EVENT_CTRL_CH_RANGE`` control event changes flag. See
V4L2 in Linux 3.10
1. Removed obsolete and unused DV_PRESET ioctls VIDIOC_G_DV_PRESET,
VIDIOC_ENUM_DV_PRESET. Remove the related v4l2_input/output
capability flags V4L2_IN_CAP_PRESETS and V4L2_OUT_CAP_PRESETS.
2. Added new debugging ioctl
V4L2 in Linux 3.11
1. Remove obsolete ``VIDIOC_DBG_G_CHIP_IDENT`` ioctl.
V4L2 in Linux 3.14
1. In struct :c:type:`v4l2_rect`, the type of ``width`` and
``height`` fields changed from _s32 to _u32.
V4L2 in Linux 3.15
1. Added Software Defined Radio (SDR) Interface.
V4L2 in Linux 3.16
1. Added event V4L2_EVENT_SOURCE_CHANGE.
V4L2 in Linux 3.17
1. Extended struct :c:type:`v4l2_pix_format`. Added
format flags.
2. Added compound control types and
V4L2 in Linux 3.18
1. Added ``V4L2_CID_PAN_SPEED`` and ``V4L2_CID_TILT_SPEED`` camera
V4L2 in Linux 3.19
1. Rewrote Colorspace chapter, added new enum
:c:type:`v4l2_ycbcr_encoding` and enum
:c:type:`v4l2_quantization` fields to struct
:c:type:`v4l2_pix_format`, struct
:c:type:`v4l2_pix_format_mplane` and
struct :c:type:`v4l2_mbus_framefmt`.
V4L2 in Linux 4.4
1. Renamed ``V4L2_TUNER_ADC`` to ``V4L2_TUNER_SDR``. The use of
``V4L2_TUNER_ADC`` is deprecated now.
2. Added ``V4L2_CID_RF_TUNER_RF_GAIN`` RF Tuner control.
3. Added transmitter support for Software Defined Radio (SDR) Interface.
.. _other:
Relation of V4L2 to other Linux multimedia APIs
.. _xvideo:
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 [#f1]_. 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 :ref:`video overlay interface <overlay>`. The
driver can easily determine the overlay target, i. e. 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
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
Section "Module"
Load "v4l"
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 :ref:`overlay` 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 ` <>`__. 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:
Experimental API Elements
The following V4L2 API elements are currently experimental and may
change in the future.
- :ref:`VIDIOC_DBG_G_CHIP_INFO` ioctl.
.. _obsolete:
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, :ref:`extended-controls`.
the DV Timings API (:ref:`dv-timings`).
.. [#f1]
This is not implemented in XFree86.