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+.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
+.. c:namespace:: V4L
+
+.. _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 :c: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`` :c: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 :ref:`VIDIOC_QUERYSTD` ioctl was
+renamed to :ref:`VIDIOC_ENUMSTD`,
+:ref:`VIDIOC_G_INPUT <VIDIOC_G_INPUT>` to
+: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 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_G_CTRL <VIDIOC_G_CTRL>` and
+: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
+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. struct 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
+
+ .. code-block:: c
+
+ err = ioctl (fd, VIDIOC_XXX, V4L2_XXX);
+
+ becomes
+
+ .. 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_G_FMT <VIDIOC_G_FMT>` and
+ :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_G_INFMT``, ``VIDIOC_S_OUTFMT``, ``VIDIOC_G_OUTFMT``,
+ ``VIDIOC_S_VBIFMT`` and ``VIDIOC_G_VBIFMT``. The image format
+ struct v4l2_format was renamed to struct v4l2_pix_format, while
+ struct 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 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 struct 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 struct 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 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
+:ref:`VIDIOC_G_FREQUENCY <VIDIOC_G_FREQUENCY>` and
+: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 ``v4l2_fmt`` ``type`` field does not contain
+``V4L2_BUF_TYPE_VBI``. In the documentation of the struct v4l2_vbi_format`,
+the ``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 :c: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
+ :ref:`open`.
+
+3. The struct 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_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
+ :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 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 v4l2_output lost its
+ ``capability`` and ``assoc_audio`` fields. ``audioset``,
+ ``modulator`` and ``std`` where added instead.
+
+5. The struct 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 v4l2_audioout field ``audio`` was renamed
+ to ``index``.
+
+6. The struct 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 v4l2_input.
+ A ``type`` field was added.
+
+ Accordingly in struct v4l2_modulator the
+ ``output`` was replaced by an ``index`` field.
+
+ In struct 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 v4l2_standard an
+ ``index`` field was added for
+ :ref:`VIDIOC_ENUMSTD`. A
+ :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
+ removed.
+
+ Struct ``v4l2_enumstd`` ceased to be.
+ :ref:`VIDIOC_ENUMSTD` now takes a pointer to a
+ struct v4l2_standard directly. The
+ information which standards are supported by a particular video
+ input or output moved into struct v4l2_input
+ and struct v4l2_output fields named ``std``,
+ respectively.
+
+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 v4l2_format the ``fmt`` union was
+ extended to contain struct 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 v4l2_buf_type and
+ the buffer type names changed as follows.
+
+
+ .. flat-table::
+ :header-rows: 1
+ :stub-columns: 0
+
+ * - Old defines
+ - enum 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`` (but this is deprecated)
+
+10. In struct v4l2_fmtdesc a enum v4l2_buf_type field named ``type`` was
+ added as in struct 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 ``V4L2_BUF_TYPE_VIDEO_OVERLAY``.
+
+11. In struct 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 enum v4l2_field value in a
+ newly added ``field`` field.
+
+ .. flat-table::
+ :header-rows: 1
+ :stub-columns: 0
+
+ * - Old flag
+ - enum 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 enum 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 struct v4l2_requestbuffers the
+ ``type`` field was properly defined as enum v4l2_buf_type. Buffer types
+ changed as mentioned above. A new ``memory`` field of type
+ enum 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 v4l2_buffer the ``type`` field was
+ properly defined as enum v4l2_buf_type.
+ Buffer types changed as mentioned above. A ``field`` field of type
+ enum 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 enum 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 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 struct v4l2_clip the ``x``, ``y``,
+ ``width`` and ``height`` field moved into a ``c`` substructure of
+ type struct v4l2_rect. The ``x`` and ``y``
+ fields were renamed to ``left`` and ``top``, i. e. offsets to a
+ context dependent origin.
+
+16. In struct v4l2_window the ``x``, ``y``,
+ ``width`` and ``height`` field moved into a ``w`` substructure as
+ above. A ``field`` field of type enum 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 struct v4l2_crop
+ where redefined for this purpose. See :ref:`crop` for details.
+
+18. In struct 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 struct v4l2_captureparm the type of
+ the ``timeperframe`` field changed from unsigned long to
+ struct 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 v4l2_outputparm.
+
+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
+ :ref:`pixfmt`.
+
+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
+ :ref:`VIDIOC_G_AUDOUT <VIDIOC_G_AUDOUT>` and
+ :ref:`VIDIOC_ENUMAUDOUT <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 :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 v4l2_buffer. 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
+ 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 :ref:`VIDIOC_QBUF` and
+ :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctls did not mention the
+ struct 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
+ :ref:`v4l2-std-id`.
+
+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 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 v4l2_captureparm and struct v4l2_outputparm the ``timeperframe``
+ field gives the time in seconds, not microseconds.
+
+V4L2 spec erratum 2006-02-04
+============================
+
+1. The ``clips`` field in struct v4l2_window
+ must point to an array of struct 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 :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 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 v4l2_frequency before calling
+ :ref:`VIDIOC_S_FREQUENCY <VIDIOC_G_FREQUENCY>`.
+
+5. The ``reserved`` array in struct 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
+====================
+
+1. New ioctls :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`,
+ :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` and
+ :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` were added, a
+ flag to skip unsupported controls with
+ :ref:`VIDIOC_QUERYCTRL`, new control types
+ ``V4L2_CTRL_TYPE_INTEGER64`` and ``V4L2_CTRL_TYPE_CTRL_CLASS``
+ (enum v4l2_ctrl_type), and new control flags
+ ``V4L2_CTRL_FLAG_READ_ONLY``, ``V4L2_CTRL_FLAG_UPDATE``,
+ ``V4L2_CTRL_FLAG_INACTIVE`` and ``V4L2_CTRL_FLAG_SLIDER``
+ (:ref:`control-flags`). See :ref:`extended-controls` for details.
+
+V4L2 in Linux 2.6.19
+====================
+
+1. In struct 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
+ :ref:`VIDIOC_G_SLICED_VBI_CAP <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 :ref:`VIDIOC_ENUM_FRAMESIZES`
+ and
+ :ref:`VIDIOC_ENUM_FRAMEINTERVALS`
+ were added.
+
+3. A new pixel format ``V4L2_PIX_FMT_RGB444`` (:ref:`pixfmt-rgb`) was
+ added.
+
+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 enum v4l2_field 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 :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 struct v4l2_window,
+ extending the structure. This may **break compatibility** with
+ applications using a struct v4l2_window directly. However the
+ :ref:`VIDIOC_G/S/TRY_FMT <VIDIOC_G_FMT>` ioctls, which take a
+ pointer to a struct v4l2_format parent structure
+ with padding bytes at the end, are not affected.
+
+3. The format of the ``chromakey`` field in struct 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``,
+ ``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 :ref:`Camera controls class <camera-controls>` 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 :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_CID_COLOR_KILLER``.
+
+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
+====================
+
+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
+ 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_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 :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
+ ``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 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
+====================
+
+1. Added ``V4L2_CID_IRIS_ABSOLUTE`` and ``V4L2_CID_IRIS_RELATIVE``
+ 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.
+
+ 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 :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:
+ :ref:`VIDIOC_ENUM_DV_TIMINGS`,
+ :ref:`VIDIOC_QUERY_DV_TIMINGS` and
+ :ref:`VIDIOC_DV_TIMINGS_CAP`.
+
+V4L2 in Linux 3.5
+=================
+
+1. Added integer menus, the new type will be
+ V4L2_CTRL_TYPE_INTEGER_MENU.
+
+2. Added selection API for V4L2 subdev interface:
+ :ref:`VIDIOC_SUBDEV_G_SELECTION` and
+ :ref:`VIDIOC_SUBDEV_S_SELECTION <VIDIOC_SUBDEV_G_SELECTION>`.
+
+3. Added ``V4L2_COLORFX_ANTIQUE``, ``V4L2_COLORFX_ART_FREEZE``,
+ ``V4L2_COLORFX_AQUA``, ``V4L2_COLORFX_SILHOUETTE``,
+ ``V4L2_COLORFX_SOLARIZATION``, ``V4L2_COLORFX_VIVID`` and
+ ``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_CID_AUTO_N_PRESET_WHITE_BALANCE``,
+ ``V4L2_CID_IMAGE_STABILIZATION``, ``V4L2_CID_ISO_SENSITIVITY``,
+ ``V4L2_CID_ISO_SENSITIVITY_AUTO``, ``V4L2_CID_EXPOSURE_METERING``,
+ ``V4L2_CID_SCENE_MODE``, ``V4L2_CID_3A_LOCK``,
+ ``V4L2_CID_AUTO_FOCUS_START``, ``V4L2_CID_AUTO_FOCUS_STOP``,
+ ``V4L2_CID_AUTO_FOCUS_STATUS`` and ``V4L2_CID_AUTO_FOCUS_RANGE``.
+
+V4L2 in Linux 3.6
+=================
+
+1. Replaced ``input`` in struct v4l2_buffer by
+ ``reserved2`` and removed ``V4L2_BUF_FLAG_INPUT``.
+
+2. Added V4L2_CAP_VIDEO_M2M and V4L2_CAP_VIDEO_M2M_MPLANE
+ capabilities.
+
+3. Added support for frequency band enumerations:
+ :ref:`VIDIOC_ENUM_FREQ_BANDS`.
+
+V4L2 in Linux 3.9
+=================
+
+1. Added timestamp types to ``flags`` field in
+ struct v4l2_buffer. See :ref:`buffer-flags`.
+
+2. Added ``V4L2_EVENT_CTRL_CH_RANGE`` control event changes flag. See
+ :ref:`ctrl-changes-flags`.
+
+V4L2 in Linux 3.10
+==================
+
+1. Removed obsolete and unused DV_PRESET ioctls VIDIOC_G_DV_PRESET,
+ VIDIOC_S_DV_PRESET, VIDIOC_QUERY_DV_PRESET and
+ 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
+ :ref:`VIDIOC_DBG_G_CHIP_INFO`.
+
+V4L2 in Linux 3.11
+==================
+
+1. Remove obsolete ``VIDIOC_DBG_G_CHIP_IDENT`` ioctl.
+
+V4L2 in Linux 3.14
+==================
+
+1. In struct 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 v4l2_pix_format. Added
+ format flags.
+
+2. Added compound control types and
+ :ref:`VIDIOC_QUERY_EXT_CTRL <VIDIOC_QUERYCTRL>`.
+
+V4L2 in Linux 3.18
+==================
+
+1. Added ``V4L2_CID_PAN_SPEED`` and ``V4L2_CID_TILT_SPEED`` camera
+ controls.
+
+V4L2 in Linux 3.19
+==================
+
+1. Rewrote Colorspace chapter, added new enum v4l2_ycbcr_encoding
+ and enum v4l2_quantization fields to struct v4l2_pix_format,
+ struct v4l2_pix_format_mplane and struct 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
+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 :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 `https://linuxtv.org <https://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:
+
+Experimental API Elements
+=========================
+
+The following V4L2 API elements are currently experimental and may
+change in the future.
+
+- :ref:`VIDIOC_DBG_G_REGISTER` and
+ :ref:`VIDIOC_DBG_S_REGISTER <VIDIOC_DBG_G_REGISTER>` ioctls.
+
+- :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`.
+
+- VIDIOC_G_DV_PRESET, VIDIOC_S_DV_PRESET,
+ VIDIOC_ENUM_DV_PRESETS and VIDIOC_QUERY_DV_PRESET ioctls. Use
+ the DV Timings API (:ref:`dv-timings`).
+
+- ``VIDIOC_SUBDEV_G_CROP`` and ``VIDIOC_SUBDEV_S_CROP`` ioctls. Use
+ ``VIDIOC_SUBDEV_G_SELECTION`` and ``VIDIOC_SUBDEV_S_SELECTION``,
+ :ref:`VIDIOC_SUBDEV_G_SELECTION`.
+
+.. [#f1]
+ This is not implemented in XFree86.