Documentation/userspace-api/media/v4l/hist-v4l2.rst
.. 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.
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 direction 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.
1999-01-27: There is now one QBUF ioctl, VIDIOC_QWBUF and VIDIOC_QRBUF are gone. VIDIOC_QBUF takes a v4l2_buffer as a parameter. Added digital zoom (cropping) controls.
Added a v4l to V4L2 ioctl compatibility layer to videodev.c. Driver writers, this changes how you implement your ioctl handler. See the Driver Writer's Guide. Added some more control id codes.
1999-03-18: Fill in the category and catname fields of v4l2_queryctrl objects before passing them to the driver. Required a minor change to the VIDIOC_QUERYCTRL handlers in the sample drivers.
1999-03-31: Better compatibility for v4l memory capture ioctls. Requires changes to drivers to fully support new compatibility features, see Driver Writer's Guide and v4l2cap.c. Added new control IDs: V4L2_CID_HFLIP, _VFLIP. Changed V4L2_PIX_FMT_YUV422P to _YUV422P, and _YUV411P to _YUV411P.
1999-04-04: Added a few more control IDs.
1999-04-07: Added the button control type.
1999-05-02: Fixed a typo in videodev.h, and added the V4L2_CTRL_FLAG_GRAYED (later V4L2_CTRL_FLAG_GRABBED) flag.
1999-05-20: Definition of VIDIOC_G_CTRL was wrong causing a malfunction of this ioctl.
1999-06-05: Changed the value of V4L2_CID_WHITENESS.
Version 0.20 introduced a number of changes which were not backward compatible with 0.19 and earlier versions. Purpose of these changes was to simplify the API, while making it more extensible and following common Linux driver API conventions.
Some typos in V4L2_FMT_FLAG symbols were fixed. struct v4l2_clip
was changed for compatibility with v4l. (1999-08-30)
V4L2_TUNER_SUB_LANG1 was added. (1999-09-05)
All ioctl() commands that used an integer argument now take a pointer to an integer. Where it makes sense, ioctls will return the actual new value in the integer pointed to by the argument, a common convention in the V4L2 API. The affected ioctls are: VIDIOC_PREVIEW, VIDIOC_STREAMON, VIDIOC_STREAMOFF, VIDIOC_S_FREQ, VIDIOC_S_INPUT, VIDIOC_S_OUTPUT, VIDIOC_S_EFFECT. For example
.. code-block:: c
err = ioctl (fd, VIDIOC_XXX, V4L2_XXX);
becomes
.. code-block:: c
int a = V4L2_XXX; err = ioctl(fd, VIDIOC_XXX, &a);
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 enveloping structure
for all format negotiations.
Similar to the changes above, the VIDIOC_G_PARM and
VIDIOC_S_PARM ioctls were merged with VIDIOC_G_OUTPARM and
VIDIOC_S_OUTPARM. A type field in the new struct v4l2_streamparm
selects the respective union member.
This change obsoletes the VIDIOC_G_OUTPARM and
VIDIOC_S_OUTPARM ioctls.
Control enumeration was simplified, and two new control flags were
introduced and one dropped. The catname field was replaced by a
group field.
Drivers can now flag unsupported and temporarily unavailable controls
with V4L2_CTRL_FLAG_DISABLED and V4L2_CTRL_FLAG_GRABBED
respectively. The group name indicates a possibly narrower
classification than the category. In other words, there may be
multiple groups within a category. Controls within a group would
typically be drawn within a group box. Controls in different
categories might have a greater separation, or may even appear in
separate windows.
The 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.
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.
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".
A number of changes were made to the raw VBI interface.
Figures clarifying the line numbering scheme were added to the V4L2
API specification. The start\ [0] and start\ [1] fields no
longer count line numbers beginning at zero. Rationale: a) The
previous definition was unclear. b) The start\ [] values are
ordinal numbers. c) There is no point in inventing a new line
numbering scheme. We now use line number as defined by ITU-R, period.
Compatibility: Add one to the start values. Applications depending on
the previous semantics may not function correctly.
The restriction "count[0] > 0 and count[1] > 0" has been relaxed to
"(count[0] + count[1]) > 0". Rationale: Drivers may allocate
resources at scan line granularity and some data services are
transmitted only on the first field. The comment that both count
values will usually be equal is misleading and pointless and has been
removed. This change breaks compatibility with earlier versions:
Drivers may return EINVAL, applications may not function correctly.
Drivers are again permitted to return negative (unknown) start values
as proposed earlier. Why this feature was dropped is unclear. This
change may break compatibility with applications depending on the
start values being positive. The use of EBUSY and EINVAL
error codes with the :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.
New buffer types V4L2_TYPE_VBI_INPUT and V4L2_TYPE_VBI_OUTPUT
were added. The former is an alias for the old V4L2_TYPE_VBI, the
latter was missing in the videodev.h file.
Added sliced VBI interface proposal.
Around October-November 2002, prior to an announced feature freeze of Linux 2.5, the API was revised, drawing from experience with V4L2 0.20. This unnamed version was finally merged into Linux 2.5.46.
As specified in :ref:related, drivers must make related device
functions available under all minor device numbers.
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.
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.
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.
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.
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).
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.
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.
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
V4L2_BUF_TYPE_CAPTUREV4L2_BUF_TYPE_VIDEO_CAPTUREV4L2_BUF_TYPE_CODECINV4L2_BUF_TYPE_CODECOUTV4L2_BUF_TYPE_EFFECTSINV4L2_BUF_TYPE_EFFECTSIN2V4L2_BUF_TYPE_EFFECTSOUTV4L2_BUF_TYPE_VIDEOOUTV4L2_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_OUTPUTV4L2_BUF_TYPE_PRIVATE_BASEV4L2_BUF_TYPE_PRIVATE (but this is deprecated)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.
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
V4L2_FMT_FLAG_NOT_INTERLACEDV4L2_FMT_FLAG_INTERLACED = V4L2_FMT_FLAG_COMBINEDV4L2_FIELD_INTERLACEDV4L2_FMT_FLAG_TOPFIELD = V4L2_FMT_FLAG_ODDFIELDV4L2_FIELD_TOPV4L2_FMT_FLAG_BOTFIELD = V4L2_FMT_FLAG_EVENFIELDV4L2_FIELD_BOTTOM-V4L2_FIELD_SEQ_TB-V4L2_FIELD_SEQ_BT-V4L2_FIELD_ALTERNATEThe 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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
The example transformation from RGB to YCbCr color space in the old
V4L2 documentation was inaccurate, this has been corrected in
:ref:pixfmt.
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.
An optional driver access priority mechanism was added, see
:ref:app-pri for details.
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.
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.
: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.
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.
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
V4L2_PIX_FMT_RGB24V4L2_PIX_FMT_BGR24V4L2_PIX_FMT_RGB32V4L2_PIX_FMT_BGR32The 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.
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.
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.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.The return value of the :ref:func-open function was incorrectly
documented.
Audio output ioctls end in -AUDOUT, not -AUDIOOUT.
In the Current Audio Input example the VIDIOC_G_AUDIO ioctl took
the wrong argument.
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.
sliced and replaces the interface first proposed in V4L2
specification 0.8.The :ref:VIDIOC_LOG_STATUS ioctl was added.
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.
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.)
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.
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.)
: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.
timeperframe
field gives the time in seconds, not microseconds.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.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.
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.
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.
In :ref:VIDIOC_G_AUDIO <VIDIOC_G_AUDIO> it was clarified that the
struct v4l2_audio mode field is a flags field.
:ref:VIDIOC_QUERYCAP did not mention the sliced VBI and radio
capability flags.
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>.
The reserved array in struct v4l2_requestbuffers has 2 elements,
not 32.
In :ref:output and :ref:raw-vbi the device file names
/dev/vout which never caught on were replaced by /dev/video.
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.
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.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.
The ioctls :ref:VIDIOC_ENUM_FRAMESIZES
and
:ref:VIDIOC_ENUM_FRAMEINTERVALS
were added.
A new pixel format V4L2_PIX_FMT_RGB444 (:ref:pixfmt-rgb) was
added.
V4L2_PIX_FMT_HM12 (:ref:reserved-formats) is a YUV 4:2:0, not
4:2:2 format.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.Two new field orders V4L2_FIELD_INTERLACED_TB and
V4L2_FIELD_INTERLACED_BT were added. See enum v4l2_field for
details.
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.
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_PIX_FMT_PAL8, V4L2_PIX_FMT_YUV444,
V4L2_PIX_FMT_YUV555, V4L2_PIX_FMT_YUV565 and
V4L2_PIX_FMT_YUV32 were added.The pixel formats :ref:V4L2_PIX_FMT_Y16 <V4L2-PIX-FMT-Y16> and
:ref:V4L2_PIX_FMT_SBGGR16 <V4L2-PIX-FMT-SBGGR16> were added.
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.
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.
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.
The pixel formats V4L2_PIX_FMT_Y16 and V4L2_PIX_FMT_SBGGR16
were added.
Added user controls V4L2_CID_CHROMA_AGC and
V4L2_CID_COLOR_KILLER.
The :ref:VIDIOC_S_HW_FREQ_SEEK ioctl
and the V4L2_CAP_HW_FREQ_SEEK capability were added.
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.
Added V4L2_MPEG_AUDIO_ENCODING_AAC and
V4L2_MPEG_AUDIO_ENCODING_AC3 MPEG audio encodings.
Added V4L2_MPEG_VIDEO_ENCODING_MPEG_4_AVC MPEG video encoding.
The pixel formats V4L2_PIX_FMT_SGRBG10 and
V4L2_PIX_FMT_SGRBG10DPCM8 were added.
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.
The pixel formats V4L2_PIX_FMT_VYUY, V4L2_PIX_FMT_NV16 and
V4L2_PIX_FMT_NV61 were added.
Added camera controls V4L2_CID_ZOOM_ABSOLUTE,
V4L2_CID_ZOOM_RELATIVE, V4L2_CID_ZOOM_CONTINUOUS and
V4L2_CID_PRIVACY.
New control flag V4L2_CTRL_FLAG_WRITE_ONLY was added.
New control V4L2_CID_COLORFX was added.
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.
Finalized the RDS capture API. See :ref:rds for more information.
Added new capabilities for modulators and RDS encoders.
Add description for libv4l API.
Added support for string controls via new type
V4L2_CTRL_TYPE_STRING.
Added V4L2_CID_BAND_STOP_FILTER documentation.
Added FM Modulator (FM TX) Extended Control Class:
V4L2_CTRL_CLASS_FM_TX and their Control IDs.
Added FM Receiver (FM RX) Extended Control Class:
V4L2_CTRL_CLASS_FM_RX and their Control IDs.
Added Remote Controller chapter, describing the default Remote Controller mapping for media devices.
V4L2_CID_IRIS_ABSOLUTE and V4L2_CID_IRIS_RELATIVE
controls to the :ref:Camera controls class <camera-controls>.The old VIDIOC_*_OLD symbols and V4L1 support were removed.
Multi-planar API added. Does not affect the compatibility of current
drivers and applications. See :ref:multi-planar API <planar-apis>
for details.
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_CTRL_FLAG_VOLATILE was added to signal volatile controls to userspace.
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.
Added V4L2_CID_ALPHA_COMPONENT control to the
:ref:User controls class <control>.
Added the device_caps field to struct v4l2_capabilities and added the new V4L2_CAP_DEVICE_CAPS capability.
Added :ref:JPEG compression control class <jpeg-controls>.
Extended the DV Timings API:
:ref:VIDIOC_ENUM_DV_TIMINGS,
:ref:VIDIOC_QUERY_DV_TIMINGS and
:ref:VIDIOC_DV_TIMINGS_CAP.
Added integer menus, the new type will be V4L2_CTRL_TYPE_INTEGER_MENU.
Added selection API for V4L2 subdev interface:
:ref:VIDIOC_SUBDEV_G_SELECTION and
:ref:VIDIOC_SUBDEV_S_SELECTION <VIDIOC_SUBDEV_G_SELECTION>.
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.
Added V4L2_CID_COLORFX_CBCR control.
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.
Replaced input in struct v4l2_buffer by
reserved2 and removed V4L2_BUF_FLAG_INPUT.
Added V4L2_CAP_VIDEO_M2M and V4L2_CAP_VIDEO_M2M_MPLANE capabilities.
Added support for frequency band enumerations:
:ref:VIDIOC_ENUM_FREQ_BANDS.
Added timestamp types to flags field in
struct v4l2_buffer. See :ref:buffer-flags.
Added V4L2_EVENT_CTRL_CH_RANGE control event changes flag. See
:ref:ctrl-changes-flags.
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.
Added new debugging ioctl
:ref:VIDIOC_DBG_G_CHIP_INFO.
VIDIOC_DBG_G_CHIP_IDENT ioctl.width and
height fields changed from _s32 to _u32.Extended struct v4l2_pix_format. Added format flags.
Added compound control types and
:ref:VIDIOC_QUERY_EXT_CTRL <VIDIOC_QUERYCTRL>.
V4L2_CID_PAN_SPEED and V4L2_CID_TILT_SPEED camera
controls.Renamed V4L2_TUNER_ADC to V4L2_TUNER_SDR. The use of
V4L2_TUNER_ADC is deprecated now.
Added V4L2_CID_RF_TUNER_RF_GAIN RF Tuner control.
Added transmitter support for Software Defined Radio (SDR) Interface.
.. _other:
.. _xvideo:
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.
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.
[to do - OSS/ALSA]
.. _experimental:
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:
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.