1 .. Permission is granted to copy, distribute and/or modify this
2 .. document under the terms of the GNU Free Documentation License,
3 .. Version 1.1 or any later version published by the Free Software
4 .. Foundation, with no Invariant Sections, no Front-Cover Texts
5 .. and no Back-Cover Texts. A copy of the license is included at
6 .. Documentation/media/uapi/fdl-appendix.rst.
8 .. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections
16 A buffer contains data exchanged by application and driver using one of
17 the Streaming I/O methods. In the multi-planar API, the data is held in
18 planes, while the buffer structure acts as a container for the planes.
19 Only pointers to buffers (planes) are exchanged, the data itself is not
20 copied. These pointers, together with meta-information like timestamps
21 or field parity, are stored in a struct :c:type:`v4l2_buffer`,
22 argument to the :ref:`VIDIOC_QUERYBUF`,
23 :ref:`VIDIOC_QBUF <VIDIOC_QBUF>` and
24 :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl. In the multi-planar API,
25 some plane-specific members of struct :c:type:`v4l2_buffer`,
26 such as pointers and sizes for each plane, are stored in struct
27 struct :c:type:`v4l2_plane` instead. In that case, struct
28 struct :c:type:`v4l2_buffer` contains an array of plane structures.
30 Dequeued video buffers come with timestamps. The driver decides at which
31 part of the frame and with which clock the timestamp is taken. Please
32 see flags in the masks ``V4L2_BUF_FLAG_TIMESTAMP_MASK`` and
33 ``V4L2_BUF_FLAG_TSTAMP_SRC_MASK`` in :ref:`buffer-flags`. These flags
34 are always valid and constant across all buffers during the whole video
35 stream. Changes in these flags may take place as a side effect of
36 :ref:`VIDIOC_S_INPUT <VIDIOC_G_INPUT>` or
37 :ref:`VIDIOC_S_OUTPUT <VIDIOC_G_OUTPUT>` however. The
38 ``V4L2_BUF_FLAG_TIMESTAMP_COPY`` timestamp type which is used by e.g. on
39 mem-to-mem devices is an exception to the rule: the timestamp source
40 flags are copied from the OUTPUT video buffer to the CAPTURE video
44 Interactions between formats, controls and buffers
45 ==================================================
47 V4L2 exposes parameters that influence the buffer size, or the way data is
48 laid out in the buffer. Those parameters are exposed through both formats and
49 controls. One example of such a control is the ``V4L2_CID_ROTATE`` control
50 that modifies the direction in which pixels are stored in the buffer, as well
51 as the buffer size when the selected format includes padding at the end of
54 The set of information needed to interpret the content of a buffer (e.g. the
55 pixel format, the line stride, the tiling orientation or the rotation) is
56 collectively referred to in the rest of this section as the buffer layout.
58 Controls that can modify the buffer layout shall set the
59 ``V4L2_CTRL_FLAG_MODIFY_LAYOUT`` flag.
61 Modifying formats or controls that influence the buffer size or layout require
62 the stream to be stopped. Any attempt at such a modification while the stream
63 is active shall cause the ioctl setting the format or the control to return
64 the ``EBUSY`` error code. In that case drivers shall also set the
65 ``V4L2_CTRL_FLAG_GRABBED`` flag when calling
66 :c:func:`VIDIOC_QUERYCTRL` or :c:func:`VIDIOC_QUERY_EXT_CTRL` for such a
67 control while the stream is active.
71 The :c:func:`VIDIOC_S_SELECTION` ioctl can, depending on the hardware (for
72 instance if the device doesn't include a scaler), modify the format in
73 addition to the selection rectangle. Similarly, the
74 :c:func:`VIDIOC_S_INPUT`, :c:func:`VIDIOC_S_OUTPUT`, :c:func:`VIDIOC_S_STD`
75 and :c:func:`VIDIOC_S_DV_TIMINGS` ioctls can also modify the format and
76 selection rectangles. When those ioctls result in a buffer size or layout
77 change, drivers shall handle that condition as they would handle it in the
78 :c:func:`VIDIOC_S_FMT` ioctl in all cases described in this section.
80 Controls that only influence the buffer layout can be modified at any time
81 when the stream is stopped. As they don't influence the buffer size, no
82 special handling is needed to synchronize those controls with buffer
83 allocation and the ``V4L2_CTRL_FLAG_GRABBED`` flag is cleared once the
86 Formats and controls that influence the buffer size interact with buffer
87 allocation. The simplest way to handle this is for drivers to always require
88 buffers to be reallocated in order to change those formats or controls. In
89 that case, to perform such changes, userspace applications shall first stop
90 the video stream with the :c:func:`VIDIOC_STREAMOFF` ioctl if it is running
91 and free all buffers with the :c:func:`VIDIOC_REQBUFS` ioctl if they are
92 allocated. After freeing all buffers the ``V4L2_CTRL_FLAG_GRABBED`` flag
93 for controls is cleared. The format or controls can then be modified, and
94 buffers shall then be reallocated and the stream restarted. A typical ioctl
105 The second :c:func:`VIDIOC_REQBUFS` call will take the new format and control
106 value into account to compute the buffer size to allocate. Applications can
107 also retrieve the size by calling the :c:func:`VIDIOC_G_FMT` ioctl if needed.
111 The API doesn't mandate the above order for control (3.) and format (4.)
112 changes. Format and controls can be set in a different order, or even
113 interleaved, depending on the device and use case. For instance some
114 controls might behave differently for different pixel formats, in which
115 case the format might need to be set first.
117 When reallocation is required, any attempt to modify format or controls that
118 influences the buffer size while buffers are allocated shall cause the format
119 or control set ioctl to return the ``EBUSY`` error. Any attempt to queue a
120 buffer too small for the current format or controls shall cause the
121 :c:func:`VIDIOC_QBUF` ioctl to return a ``EINVAL`` error.
123 Buffer reallocation is an expensive operation. To avoid that cost, drivers can
124 (and are encouraged to) allow format or controls that influence the buffer
125 size to be changed with buffers allocated. In that case, a typical ioctl
126 sequence to modify format and controls is
129 #. VIDIOC_S_EXT_CTRLS
134 For this sequence to operate correctly, queued buffers need to be large enough
135 for the new format or controls. Drivers shall return a ``ENOSPC`` error in
136 response to format change (:c:func:`VIDIOC_S_FMT`) or control changes
137 (:c:func:`VIDIOC_S_CTRL` or :c:func:`VIDIOC_S_EXT_CTRLS`) if buffers too small
138 for the new format are currently queued. As a simplification, drivers are
139 allowed to return a ``EBUSY`` error from these ioctls if any buffer is
140 currently queued, without checking the queued buffers sizes.
142 Additionally, drivers shall return a ``EINVAL`` error from the
143 :c:func:`VIDIOC_QBUF` ioctl if the buffer being queued is too small for the
144 current format or controls. Together, these requirements ensure that queued
145 buffers will always be large enough for the configured format and controls.
147 Userspace applications can query the buffer size required for a given format
148 and controls by first setting the desired control values and then trying the
149 desired format. The :c:func:`VIDIOC_TRY_FMT` ioctl will return the required
152 #. VIDIOC_S_EXT_CTRLS(x)
154 #. VIDIOC_S_EXT_CTRLS(y)
157 The :c:func:`VIDIOC_CREATE_BUFS` ioctl can then be used to allocate buffers
158 based on the queried sizes (for instance by allocating a set of buffers large
159 enough for all the desired formats and controls, or by allocating separate set
160 of appropriately sized buffers for each use case).
163 .. c:type:: v4l2_buffer
168 .. tabularcolumns:: |p{2.8cm}|p{2.5cm}|p{1.3cm}|p{10.5cm}|
170 .. cssclass:: longtable
172 .. flat-table:: struct v4l2_buffer
180 - Number of the buffer, set by the application except when calling
181 :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>`, then it is set by the
182 driver. This field can range from zero to the number of buffers
183 allocated with the :ref:`VIDIOC_REQBUFS` ioctl
184 (struct :c:type:`v4l2_requestbuffers`
185 ``count``), plus any buffers allocated with
186 :ref:`VIDIOC_CREATE_BUFS` minus one.
190 - Type of the buffer, same as struct
191 :c:type:`v4l2_format` ``type`` or struct
192 :c:type:`v4l2_requestbuffers` ``type``, set
193 by the application. See :c:type:`v4l2_buf_type`
197 - The number of bytes occupied by the data in the buffer. It depends
198 on the negotiated data format and may change with each buffer for
199 compressed variable size data like JPEG images. Drivers must set
200 this field when ``type`` refers to a capture stream, applications
201 when it refers to an output stream. If the application sets this
202 to 0 for an output stream, then ``bytesused`` will be set to the
203 size of the buffer (see the ``length`` field of this struct) by
204 the driver. For multiplanar formats this field is ignored and the
205 ``planes`` pointer is used instead.
209 - Flags set by the application or driver, see :ref:`buffer-flags`.
213 - Indicates the field order of the image in the buffer, see
214 :c:type:`v4l2_field`. This field is not used when the buffer
215 contains VBI data. Drivers must set it when ``type`` refers to a
216 capture stream, applications when it refers to an output stream.
220 - For capture streams this is time when the first data byte was
221 captured, as returned by the :c:func:`clock_gettime()` function
222 for the relevant clock id; see ``V4L2_BUF_FLAG_TIMESTAMP_*`` in
223 :ref:`buffer-flags`. For output streams the driver stores the
224 time at which the last data byte was actually sent out in the
225 ``timestamp`` field. This permits applications to monitor the
226 drift between the video and system clock. For output streams that
227 use ``V4L2_BUF_FLAG_TIMESTAMP_COPY`` the application has to fill
228 in the timestamp which will be copied by the driver to the capture
230 * - struct :c:type:`v4l2_timecode`
233 - When ``type`` is ``V4L2_BUF_TYPE_VIDEO_CAPTURE`` and the
234 ``V4L2_BUF_FLAG_TIMECODE`` flag is set in ``flags``, this
235 structure contains a frame timecode. In
236 :c:type:`V4L2_FIELD_ALTERNATE <v4l2_field>` mode the top and
237 bottom field contain the same timecode. Timecodes are intended to
238 help video editing and are typically recorded on video tapes, but
239 also embedded in compressed formats like MPEG. This field is
240 independent of the ``timestamp`` and ``sequence`` fields.
244 - Set by the driver, counting the frames (not fields!) in sequence.
245 This field is set for both input and output devices.
248 In :c:type:`V4L2_FIELD_ALTERNATE <v4l2_field>` mode the top and
249 bottom field have the same sequence number. The count starts at
250 zero and includes dropped or repeated frames. A dropped frame was
251 received by an input device but could not be stored due to lack of
252 free buffer space. A repeated frame was displayed again by an
253 output device because the application did not pass new data in
258 This may count the frames received e.g. over USB, without
259 taking into account the frames dropped by the remote hardware due
260 to limited compression throughput or bus bandwidth. These devices
261 identify by not enumerating any video standards, see
267 - This field must be set by applications and/or drivers in
268 accordance with the selected I/O method. See :c:type:`v4l2_memory`
274 - For the single-planar API and when ``memory`` is
275 ``V4L2_MEMORY_MMAP`` this is the offset of the buffer from the
276 start of the device memory. The value is returned by the driver
277 and apart of serving as parameter to the
278 :ref:`mmap() <func-mmap>` function not useful for applications.
279 See :ref:`mmap` for details
283 - For the single-planar API and when ``memory`` is
284 ``V4L2_MEMORY_USERPTR`` this is a pointer to the buffer (casted to
285 unsigned long type) in virtual memory, set by the application. See
286 :ref:`userp` for details.
290 - When using the multi-planar API, contains a userspace pointer to
291 an array of struct :c:type:`v4l2_plane`. The size of
292 the array should be put in the ``length`` field of this
293 struct :c:type:`v4l2_buffer` structure.
297 - For the single-plane API and when ``memory`` is
298 ``V4L2_MEMORY_DMABUF`` this is the file descriptor associated with
303 - Size of the buffer (not the payload) in bytes for the
304 single-planar API. This is set by the driver based on the calls to
305 :ref:`VIDIOC_REQBUFS` and/or
306 :ref:`VIDIOC_CREATE_BUFS`. For the
307 multi-planar API the application sets this to the number of
308 elements in the ``planes`` array. The driver will fill in the
309 actual number of valid elements in that array.
313 - A place holder for future extensions. Drivers and applications
318 - The file descriptor of the request to queue the buffer to. If the flag
319 ``V4L2_BUF_FLAG_REQUEST_FD`` is set, then the buffer will be
320 queued to this request. If the flag is not set, then this field will
323 The ``V4L2_BUF_FLAG_REQUEST_FD`` flag and this field are only used by
324 :ref:`ioctl VIDIOC_QBUF <VIDIOC_QBUF>` and ignored by other ioctls that
325 take a :c:type:`v4l2_buffer` as argument.
327 Applications should not set ``V4L2_BUF_FLAG_REQUEST_FD`` for any ioctls
328 other than :ref:`VIDIOC_QBUF <VIDIOC_QBUF>`.
330 If the device does not support requests, then ``EACCES`` will be returned.
331 If requests are supported but an invalid request file descriptor is
332 given, then ``EINVAL`` will be returned.
336 .. c:type:: v4l2_plane
341 .. tabularcolumns:: |p{3.5cm}|p{3.5cm}|p{3.5cm}|p{7.0cm}|
343 .. cssclass:: longtable
353 - The number of bytes occupied by data in the plane (its payload).
354 Drivers must set this field when ``type`` refers to a capture
355 stream, applications when it refers to an output stream. If the
356 application sets this to 0 for an output stream, then
357 ``bytesused`` will be set to the size of the plane (see the
358 ``length`` field of this struct) by the driver.
362 Note that the actual image data starts at ``data_offset``
367 - Size in bytes of the plane (not its payload). This is set by the
368 driver based on the calls to
369 :ref:`VIDIOC_REQBUFS` and/or
370 :ref:`VIDIOC_CREATE_BUFS`.
378 - When the memory type in the containing struct
379 :c:type:`v4l2_buffer` is ``V4L2_MEMORY_MMAP``, this
380 is the value that should be passed to :ref:`mmap() <func-mmap>`,
381 similar to the ``offset`` field in struct
382 :c:type:`v4l2_buffer`.
386 - When the memory type in the containing struct
387 :c:type:`v4l2_buffer` is ``V4L2_MEMORY_USERPTR``,
388 this is a userspace pointer to the memory allocated for this plane
393 - When the memory type in the containing struct
394 :c:type:`v4l2_buffer` is ``V4L2_MEMORY_DMABUF``,
395 this is a file descriptor associated with a DMABUF buffer, similar
396 to the ``fd`` field in struct :c:type:`v4l2_buffer`.
400 - Offset in bytes to video data in the plane. Drivers must set this
401 field when ``type`` refers to a capture stream, applications when
402 it refers to an output stream.
406 That data_offset is included in ``bytesused``. So the
407 size of the image in the plane is ``bytesused``-``data_offset``
408 at offset ``data_offset`` from the start of the plane.
412 - Reserved for future use. Should be zeroed by drivers and
417 .. c:type:: v4l2_buf_type
422 .. cssclass:: longtable
424 .. tabularcolumns:: |p{7.2cm}|p{0.6cm}|p{9.7cm}|
431 * - ``V4L2_BUF_TYPE_VIDEO_CAPTURE``
433 - Buffer of a single-planar video capture stream, see
435 * - ``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE``
437 - Buffer of a multi-planar video capture stream, see
439 * - ``V4L2_BUF_TYPE_VIDEO_OUTPUT``
441 - Buffer of a single-planar video output stream, see
443 * - ``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE``
445 - Buffer of a multi-planar video output stream, see :ref:`output`.
446 * - ``V4L2_BUF_TYPE_VIDEO_OVERLAY``
448 - Buffer for video overlay, see :ref:`overlay`.
449 * - ``V4L2_BUF_TYPE_VBI_CAPTURE``
451 - Buffer of a raw VBI capture stream, see :ref:`raw-vbi`.
452 * - ``V4L2_BUF_TYPE_VBI_OUTPUT``
454 - Buffer of a raw VBI output stream, see :ref:`raw-vbi`.
455 * - ``V4L2_BUF_TYPE_SLICED_VBI_CAPTURE``
457 - Buffer of a sliced VBI capture stream, see :ref:`sliced`.
458 * - ``V4L2_BUF_TYPE_SLICED_VBI_OUTPUT``
460 - Buffer of a sliced VBI output stream, see :ref:`sliced`.
461 * - ``V4L2_BUF_TYPE_VIDEO_OUTPUT_OVERLAY``
463 - Buffer for video output overlay (OSD), see :ref:`osd`.
464 * - ``V4L2_BUF_TYPE_SDR_CAPTURE``
466 - Buffer for Software Defined Radio (SDR) capture stream, see
468 * - ``V4L2_BUF_TYPE_SDR_OUTPUT``
470 - Buffer for Software Defined Radio (SDR) output stream, see
472 * - ``V4L2_BUF_TYPE_META_CAPTURE``
474 - Buffer for metadata capture, see :ref:`metadata`.
475 * - ``V4L2_BUF_TYPE_META_OUTPUT``
477 - Buffer for metadata output, see :ref:`metadata`.
486 .. tabularcolumns:: |p{7.0cm}|p{2.2cm}|p{8.3cm}|
488 .. cssclass:: longtable
495 * .. _`V4L2-BUF-FLAG-MAPPED`:
497 - ``V4L2_BUF_FLAG_MAPPED``
499 - The buffer resides in device memory and has been mapped into the
500 application's address space, see :ref:`mmap` for details.
501 Drivers set or clear this flag when the
502 :ref:`VIDIOC_QUERYBUF`,
503 :ref:`VIDIOC_QBUF` or
504 :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl is called. Set by the
506 * .. _`V4L2-BUF-FLAG-QUEUED`:
508 - ``V4L2_BUF_FLAG_QUEUED``
510 - Internally drivers maintain two buffer queues, an incoming and
511 outgoing queue. When this flag is set, the buffer is currently on
512 the incoming queue. It automatically moves to the outgoing queue
513 after the buffer has been filled (capture devices) or displayed
514 (output devices). Drivers set or clear this flag when the
515 ``VIDIOC_QUERYBUF`` ioctl is called. After (successful) calling
516 the ``VIDIOC_QBUF``\ ioctl it is always set and after
517 ``VIDIOC_DQBUF`` always cleared.
518 * .. _`V4L2-BUF-FLAG-DONE`:
520 - ``V4L2_BUF_FLAG_DONE``
522 - When this flag is set, the buffer is currently on the outgoing
523 queue, ready to be dequeued from the driver. Drivers set or clear
524 this flag when the ``VIDIOC_QUERYBUF`` ioctl is called. After
525 calling the ``VIDIOC_QBUF`` or ``VIDIOC_DQBUF`` it is always
526 cleared. Of course a buffer cannot be on both queues at the same
527 time, the ``V4L2_BUF_FLAG_QUEUED`` and ``V4L2_BUF_FLAG_DONE`` flag
528 are mutually exclusive. They can be both cleared however, then the
529 buffer is in "dequeued" state, in the application domain so to
531 * .. _`V4L2-BUF-FLAG-ERROR`:
533 - ``V4L2_BUF_FLAG_ERROR``
535 - When this flag is set, the buffer has been dequeued successfully,
536 although the data might have been corrupted. This is recoverable,
537 streaming may continue as normal and the buffer may be reused
538 normally. Drivers set this flag when the ``VIDIOC_DQBUF`` ioctl is
540 * .. _`V4L2-BUF-FLAG-IN-REQUEST`:
542 - ``V4L2_BUF_FLAG_IN_REQUEST``
544 - This buffer is part of a request that hasn't been queued yet.
545 * .. _`V4L2-BUF-FLAG-KEYFRAME`:
547 - ``V4L2_BUF_FLAG_KEYFRAME``
549 - Drivers set or clear this flag when calling the ``VIDIOC_DQBUF``
550 ioctl. It may be set by video capture devices when the buffer
551 contains a compressed image which is a key frame (or field), i. e.
552 can be decompressed on its own. Also known as an I-frame.
553 Applications can set this bit when ``type`` refers to an output
555 * .. _`V4L2-BUF-FLAG-PFRAME`:
557 - ``V4L2_BUF_FLAG_PFRAME``
559 - Similar to ``V4L2_BUF_FLAG_KEYFRAME`` this flags predicted frames
560 or fields which contain only differences to a previous key frame.
561 Applications can set this bit when ``type`` refers to an output
563 * .. _`V4L2-BUF-FLAG-BFRAME`:
565 - ``V4L2_BUF_FLAG_BFRAME``
567 - Similar to ``V4L2_BUF_FLAG_KEYFRAME`` this flags a bi-directional
568 predicted frame or field which contains only the differences
569 between the current frame and both the preceding and following key
570 frames to specify its content. Applications can set this bit when
571 ``type`` refers to an output stream.
572 * .. _`V4L2-BUF-FLAG-TIMECODE`:
574 - ``V4L2_BUF_FLAG_TIMECODE``
576 - The ``timecode`` field is valid. Drivers set or clear this flag
577 when the ``VIDIOC_DQBUF`` ioctl is called. Applications can set
578 this bit and the corresponding ``timecode`` structure when
579 ``type`` refers to an output stream.
580 * .. _`V4L2-BUF-FLAG-PREPARED`:
582 - ``V4L2_BUF_FLAG_PREPARED``
584 - The buffer has been prepared for I/O and can be queued by the
585 application. Drivers set or clear this flag when the
586 :ref:`VIDIOC_QUERYBUF`,
587 :ref:`VIDIOC_PREPARE_BUF <VIDIOC_QBUF>`,
588 :ref:`VIDIOC_QBUF` or
589 :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl is called.
590 * .. _`V4L2-BUF-FLAG-NO-CACHE-INVALIDATE`:
592 - ``V4L2_BUF_FLAG_NO_CACHE_INVALIDATE``
594 - Caches do not have to be invalidated for this buffer. Typically
595 applications shall use this flag if the data captured in the
596 buffer is not going to be touched by the CPU, instead the buffer
597 will, probably, be passed on to a DMA-capable hardware unit for
598 further processing or output.
599 * .. _`V4L2-BUF-FLAG-NO-CACHE-CLEAN`:
601 - ``V4L2_BUF_FLAG_NO_CACHE_CLEAN``
603 - Caches do not have to be cleaned for this buffer. Typically
604 applications shall use this flag for output buffers if the data in
605 this buffer has not been created by the CPU but by some
606 DMA-capable unit, in which case caches have not been used.
607 * .. _`V4L2-BUF-FLAG-LAST`:
609 - ``V4L2_BUF_FLAG_LAST``
611 - Last buffer produced by the hardware. mem2mem codec drivers set
612 this flag on the capture queue for the last buffer when the
613 :ref:`VIDIOC_QUERYBUF` or
614 :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl is called. Due to
615 hardware limitations, the last buffer may be empty. In this case
616 the driver will set the ``bytesused`` field to 0, regardless of
617 the format. Any Any subsequent call to the
618 :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl will not block anymore,
619 but return an ``EPIPE`` error code.
620 * .. _`V4L2-BUF-FLAG-REQUEST-FD`:
622 - ``V4L2_BUF_FLAG_REQUEST_FD``
624 - The ``request_fd`` field contains a valid file descriptor.
625 * .. _`V4L2-BUF-FLAG-TIMESTAMP-MASK`:
627 - ``V4L2_BUF_FLAG_TIMESTAMP_MASK``
629 - Mask for timestamp types below. To test the timestamp type, mask
630 out bits not belonging to timestamp type by performing a logical
631 and operation with buffer flags and timestamp mask.
632 * .. _`V4L2-BUF-FLAG-TIMESTAMP-UNKNOWN`:
634 - ``V4L2_BUF_FLAG_TIMESTAMP_UNKNOWN``
636 - Unknown timestamp type. This type is used by drivers before Linux
637 3.9 and may be either monotonic (see below) or realtime (wall
638 clock). Monotonic clock has been favoured in embedded systems
639 whereas most of the drivers use the realtime clock. Either kinds
640 of timestamps are available in user space via
641 :c:func:`clock_gettime` using clock IDs ``CLOCK_MONOTONIC``
642 and ``CLOCK_REALTIME``, respectively.
643 * .. _`V4L2-BUF-FLAG-TIMESTAMP-MONOTONIC`:
645 - ``V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC``
647 - The buffer timestamp has been taken from the ``CLOCK_MONOTONIC``
648 clock. To access the same clock outside V4L2, use
649 :c:func:`clock_gettime`.
650 * .. _`V4L2-BUF-FLAG-TIMESTAMP-COPY`:
652 - ``V4L2_BUF_FLAG_TIMESTAMP_COPY``
654 - The CAPTURE buffer timestamp has been taken from the corresponding
655 OUTPUT buffer. This flag applies only to mem2mem devices.
656 * .. _`V4L2-BUF-FLAG-TSTAMP-SRC-MASK`:
658 - ``V4L2_BUF_FLAG_TSTAMP_SRC_MASK``
660 - Mask for timestamp sources below. The timestamp source defines the
661 point of time the timestamp is taken in relation to the frame.
662 Logical 'and' operation between the ``flags`` field and
663 ``V4L2_BUF_FLAG_TSTAMP_SRC_MASK`` produces the value of the
664 timestamp source. Applications must set the timestamp source when
665 ``type`` refers to an output stream and
666 ``V4L2_BUF_FLAG_TIMESTAMP_COPY`` is set.
667 * .. _`V4L2-BUF-FLAG-TSTAMP-SRC-EOF`:
669 - ``V4L2_BUF_FLAG_TSTAMP_SRC_EOF``
671 - End Of Frame. The buffer timestamp has been taken when the last
672 pixel of the frame has been received or the last pixel of the
673 frame has been transmitted. In practice, software generated
674 timestamps will typically be read from the clock a small amount of
675 time after the last pixel has been received or transmitten,
676 depending on the system and other activity in it.
677 * .. _`V4L2-BUF-FLAG-TSTAMP-SRC-SOE`:
679 - ``V4L2_BUF_FLAG_TSTAMP_SRC_SOE``
681 - Start Of Exposure. The buffer timestamp has been taken when the
682 exposure of the frame has begun. This is only valid for the
683 ``V4L2_BUF_TYPE_VIDEO_CAPTURE`` buffer type.
687 .. c:type:: v4l2_memory
692 .. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|
699 * - ``V4L2_MEMORY_MMAP``
701 - The buffer is used for :ref:`memory mapping <mmap>` I/O.
702 * - ``V4L2_MEMORY_USERPTR``
704 - The buffer is used for :ref:`user pointer <userp>` I/O.
705 * - ``V4L2_MEMORY_OVERLAY``
708 * - ``V4L2_MEMORY_DMABUF``
710 - The buffer is used for :ref:`DMA shared buffer <dmabuf>` I/O.
717 The struct :c:type:`v4l2_timecode` structure is designed to hold a
718 :ref:`smpte12m` or similar timecode. (struct
719 struct :c:type:`timeval` timestamps are stored in struct
720 :c:type:`v4l2_buffer` field ``timestamp``.)
723 .. c:type:: v4l2_timecode
728 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
737 - Frame rate the timecodes are based on, see :ref:`timecode-type`.
740 - Timecode flags, see :ref:`timecode-flags`.
743 - Frame count, 0 ... 23/24/29/49/59, depending on the type of
747 - Seconds count, 0 ... 59. This is a binary, not BCD number.
750 - Minutes count, 0 ... 59. This is a binary, not BCD number.
753 - Hours count, 0 ... 29. This is a binary, not BCD number.
756 - The "user group" bits from the timecode.
765 .. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|
772 * - ``V4L2_TC_TYPE_24FPS``
774 - 24 frames per second, i. e. film.
775 * - ``V4L2_TC_TYPE_25FPS``
777 - 25 frames per second, i. e. PAL or SECAM video.
778 * - ``V4L2_TC_TYPE_30FPS``
780 - 30 frames per second, i. e. NTSC video.
781 * - ``V4L2_TC_TYPE_50FPS``
784 * - ``V4L2_TC_TYPE_60FPS``
795 .. tabularcolumns:: |p{6.6cm}|p{1.4cm}|p{9.5cm}|
802 * - ``V4L2_TC_FLAG_DROPFRAME``
804 - Indicates "drop frame" semantics for counting frames in 29.97 fps
805 material. When set, frame numbers 0 and 1 at the start of each
806 minute, except minutes 0, 10, 20, 30, 40, 50 are omitted from the
808 * - ``V4L2_TC_FLAG_COLORFRAME``
810 - The "color frame" flag.
811 * - ``V4L2_TC_USERBITS_field``
813 - Field mask for the "binary group flags".
814 * - ``V4L2_TC_USERBITS_USERDEFINED``
816 - Unspecified format.
817 * - ``V4L2_TC_USERBITS_8BITCHARS``
819 - 8-bit ISO characters.