1 .. -*- coding: utf-8; mode: rst -*-
9 A buffer contains data exchanged by application and driver using one of
10 the Streaming I/O methods. In the multi-planar API, the data is held in
11 planes, while the buffer structure acts as a container for the planes.
12 Only pointers to buffers (planes) are exchanged, the data itself is not
13 copied. These pointers, together with meta-information like timestamps
14 or field parity, are stored in a struct :c:type:`v4l2_buffer`,
15 argument to the :ref:`VIDIOC_QUERYBUF`,
16 :ref:`VIDIOC_QBUF <VIDIOC_QBUF>` and
17 :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl. In the multi-planar API,
18 some plane-specific members of struct :c:type:`v4l2_buffer`,
19 such as pointers and sizes for each plane, are stored in struct
20 struct :c:type:`v4l2_plane` instead. In that case, struct
21 struct :c:type:`v4l2_buffer` contains an array of plane structures.
23 Dequeued video buffers come with timestamps. The driver decides at which
24 part of the frame and with which clock the timestamp is taken. Please
25 see flags in the masks ``V4L2_BUF_FLAG_TIMESTAMP_MASK`` and
26 ``V4L2_BUF_FLAG_TSTAMP_SRC_MASK`` in :ref:`buffer-flags`. These flags
27 are always valid and constant across all buffers during the whole video
28 stream. Changes in these flags may take place as a side effect of
29 :ref:`VIDIOC_S_INPUT <VIDIOC_G_INPUT>` or
30 :ref:`VIDIOC_S_OUTPUT <VIDIOC_G_OUTPUT>` however. The
31 ``V4L2_BUF_FLAG_TIMESTAMP_COPY`` timestamp type which is used by e.g. on
32 mem-to-mem devices is an exception to the rule: the timestamp source
33 flags are copied from the OUTPUT video buffer to the CAPTURE video
37 Interactions between formats, controls and buffers
38 ==================================================
40 V4L2 exposes parameters that influence the buffer size, or the way data is
41 laid out in the buffer. Those parameters are exposed through both formats and
42 controls. One example of such a control is the ``V4L2_CID_ROTATE`` control
43 that modifies the direction in which pixels are stored in the buffer, as well
44 as the buffer size when the selected format includes padding at the end of
47 The set of information needed to interpret the content of a buffer (e.g. the
48 pixel format, the line stride, the tiling orientation or the rotation) is
49 collectively referred to in the rest of this section as the buffer layout.
51 Controls that can modify the buffer layout shall set the
52 ``V4L2_CTRL_FLAG_MODIFY_LAYOUT`` flag.
54 Modifying formats or controls that influence the buffer size or layout require
55 the stream to be stopped. Any attempt at such a modification while the stream
56 is active shall cause the ioctl setting the format or the control to return
57 the ``EBUSY`` error code. In that case drivers shall also set the
58 ``V4L2_CTRL_FLAG_GRABBED`` flag when calling
59 :c:func:`VIDIOC_QUERYCTRL` or :c:func:`VIDIOC_QUERY_EXT_CTRL` for such a
60 control while the stream is active.
64 The :c:func:`VIDIOC_S_SELECTION` ioctl can, depending on the hardware (for
65 instance if the device doesn't include a scaler), modify the format in
66 addition to the selection rectangle. Similarly, the
67 :c:func:`VIDIOC_S_INPUT`, :c:func:`VIDIOC_S_OUTPUT`, :c:func:`VIDIOC_S_STD`
68 and :c:func:`VIDIOC_S_DV_TIMINGS` ioctls can also modify the format and
69 selection rectangles. When those ioctls result in a buffer size or layout
70 change, drivers shall handle that condition as they would handle it in the
71 :c:func:`VIDIOC_S_FMT` ioctl in all cases described in this section.
73 Controls that only influence the buffer layout can be modified at any time
74 when the stream is stopped. As they don't influence the buffer size, no
75 special handling is needed to synchronize those controls with buffer
76 allocation and the ``V4L2_CTRL_FLAG_GRABBED`` flag is cleared once the
79 Formats and controls that influence the buffer size interact with buffer
80 allocation. The simplest way to handle this is for drivers to always require
81 buffers to be reallocated in order to change those formats or controls. In
82 that case, to perform such changes, userspace applications shall first stop
83 the video stream with the :c:func:`VIDIOC_STREAMOFF` ioctl if it is running
84 and free all buffers with the :c:func:`VIDIOC_REQBUFS` ioctl if they are
85 allocated. After freeing all buffers the ``V4L2_CTRL_FLAG_GRABBED`` flag
86 for controls is cleared. The format or controls can then be modified, and
87 buffers shall then be reallocated and the stream restarted. A typical ioctl
98 The second :c:func:`VIDIOC_REQBUFS` call will take the new format and control
99 value into account to compute the buffer size to allocate. Applications can
100 also retrieve the size by calling the :c:func:`VIDIOC_G_FMT` ioctl if needed.
104 The API doesn't mandate the above order for control (3.) and format (4.)
105 changes. Format and controls can be set in a different order, or even
106 interleaved, depending on the device and use case. For instance some
107 controls might behave differently for different pixel formats, in which
108 case the format might need to be set first.
110 When reallocation is required, any attempt to modify format or controls that
111 influences the buffer size while buffers are allocated shall cause the format
112 or control set ioctl to return the ``EBUSY`` error. Any attempt to queue a
113 buffer too small for the current format or controls shall cause the
114 :c:func:`VIDIOC_QBUF` ioctl to return a ``EINVAL`` error.
116 Buffer reallocation is an expensive operation. To avoid that cost, drivers can
117 (and are encouraged to) allow format or controls that influence the buffer
118 size to be changed with buffers allocated. In that case, a typical ioctl
119 sequence to modify format and controls is
122 #. VIDIOC_S_EXT_CTRLS
127 For this sequence to operate correctly, queued buffers need to be large enough
128 for the new format or controls. Drivers shall return a ``ENOSPC`` error in
129 response to format change (:c:func:`VIDIOC_S_FMT`) or control changes
130 (:c:func:`VIDIOC_S_CTRL` or :c:func:`VIDIOC_S_EXT_CTRLS`) if buffers too small
131 for the new format are currently queued. As a simplification, drivers are
132 allowed to return a ``EBUSY`` error from these ioctls if any buffer is
133 currently queued, without checking the queued buffers sizes.
135 Additionally, drivers shall return a ``EINVAL`` error from the
136 :c:func:`VIDIOC_QBUF` ioctl if the buffer being queued is too small for the
137 current format or controls. Together, these requirements ensure that queued
138 buffers will always be large enough for the configured format and controls.
140 Userspace applications can query the buffer size required for a given format
141 and controls by first setting the desired control values and then trying the
142 desired format. The :c:func:`VIDIOC_TRY_FMT` ioctl will return the required
145 #. VIDIOC_S_EXT_CTRLS(x)
147 #. VIDIOC_S_EXT_CTRLS(y)
150 The :c:func:`VIDIOC_CREATE_BUFS` ioctl can then be used to allocate buffers
151 based on the queried sizes (for instance by allocating a set of buffers large
152 enough for all the desired formats and controls, or by allocating separate set
153 of appropriately sized buffers for each use case).
156 .. c:type:: v4l2_buffer
161 .. tabularcolumns:: |p{2.8cm}|p{2.5cm}|p{1.3cm}|p{10.5cm}|
163 .. cssclass:: longtable
165 .. flat-table:: struct v4l2_buffer
173 - Number of the buffer, set by the application except when calling
174 :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>`, then it is set by the
175 driver. This field can range from zero to the number of buffers
176 allocated with the :ref:`VIDIOC_REQBUFS` ioctl
177 (struct :c:type:`v4l2_requestbuffers`
178 ``count``), plus any buffers allocated with
179 :ref:`VIDIOC_CREATE_BUFS` minus one.
183 - Type of the buffer, same as struct
184 :c:type:`v4l2_format` ``type`` or struct
185 :c:type:`v4l2_requestbuffers` ``type``, set
186 by the application. See :c:type:`v4l2_buf_type`
190 - The number of bytes occupied by the data in the buffer. It depends
191 on the negotiated data format and may change with each buffer for
192 compressed variable size data like JPEG images. Drivers must set
193 this field when ``type`` refers to a capture stream, applications
194 when it refers to an output stream. If the application sets this
195 to 0 for an output stream, then ``bytesused`` will be set to the
196 size of the buffer (see the ``length`` field of this struct) by
197 the driver. For multiplanar formats this field is ignored and the
198 ``planes`` pointer is used instead.
202 - Flags set by the application or driver, see :ref:`buffer-flags`.
206 - Indicates the field order of the image in the buffer, see
207 :c:type:`v4l2_field`. This field is not used when the buffer
208 contains VBI data. Drivers must set it when ``type`` refers to a
209 capture stream, applications when it refers to an output stream.
213 - For capture streams this is time when the first data byte was
214 captured, as returned by the :c:func:`clock_gettime()` function
215 for the relevant clock id; see ``V4L2_BUF_FLAG_TIMESTAMP_*`` in
216 :ref:`buffer-flags`. For output streams the driver stores the
217 time at which the last data byte was actually sent out in the
218 ``timestamp`` field. This permits applications to monitor the
219 drift between the video and system clock. For output streams that
220 use ``V4L2_BUF_FLAG_TIMESTAMP_COPY`` the application has to fill
221 in the timestamp which will be copied by the driver to the capture
223 * - struct :c:type:`v4l2_timecode`
226 - When ``type`` is ``V4L2_BUF_TYPE_VIDEO_CAPTURE`` and the
227 ``V4L2_BUF_FLAG_TIMECODE`` flag is set in ``flags``, this
228 structure contains a frame timecode. In
229 :c:type:`V4L2_FIELD_ALTERNATE <v4l2_field>` mode the top and
230 bottom field contain the same timecode. Timecodes are intended to
231 help video editing and are typically recorded on video tapes, but
232 also embedded in compressed formats like MPEG. This field is
233 independent of the ``timestamp`` and ``sequence`` fields.
237 - Set by the driver, counting the frames (not fields!) in sequence.
238 This field is set for both input and output devices.
241 In :c:type:`V4L2_FIELD_ALTERNATE <v4l2_field>` mode the top and
242 bottom field have the same sequence number. The count starts at
243 zero and includes dropped or repeated frames. A dropped frame was
244 received by an input device but could not be stored due to lack of
245 free buffer space. A repeated frame was displayed again by an
246 output device because the application did not pass new data in
251 This may count the frames received e.g. over USB, without
252 taking into account the frames dropped by the remote hardware due
253 to limited compression throughput or bus bandwidth. These devices
254 identify by not enumerating any video standards, see
260 - This field must be set by applications and/or drivers in
261 accordance with the selected I/O method. See :c:type:`v4l2_memory`
267 - For the single-planar API and when ``memory`` is
268 ``V4L2_MEMORY_MMAP`` this is the offset of the buffer from the
269 start of the device memory. The value is returned by the driver
270 and apart of serving as parameter to the
271 :ref:`mmap() <func-mmap>` function not useful for applications.
272 See :ref:`mmap` for details
276 - For the single-planar API and when ``memory`` is
277 ``V4L2_MEMORY_USERPTR`` this is a pointer to the buffer (casted to
278 unsigned long type) in virtual memory, set by the application. See
279 :ref:`userp` for details.
283 - When using the multi-planar API, contains a userspace pointer to
284 an array of struct :c:type:`v4l2_plane`. The size of
285 the array should be put in the ``length`` field of this
286 struct :c:type:`v4l2_buffer` structure.
290 - For the single-plane API and when ``memory`` is
291 ``V4L2_MEMORY_DMABUF`` this is the file descriptor associated with
296 - Size of the buffer (not the payload) in bytes for the
297 single-planar API. This is set by the driver based on the calls to
298 :ref:`VIDIOC_REQBUFS` and/or
299 :ref:`VIDIOC_CREATE_BUFS`. For the
300 multi-planar API the application sets this to the number of
301 elements in the ``planes`` array. The driver will fill in the
302 actual number of valid elements in that array.
306 - A place holder for future extensions. Drivers and applications
311 - The file descriptor of the request to queue the buffer to. If the flag
312 ``V4L2_BUF_FLAG_REQUEST_FD`` is set, then the buffer will be
313 queued to this request. If the flag is not set, then this field will
316 The ``V4L2_BUF_FLAG_REQUEST_FD`` flag and this field are only used by
317 :ref:`ioctl VIDIOC_QBUF <VIDIOC_QBUF>` and ignored by other ioctls that
318 take a :c:type:`v4l2_buffer` as argument.
320 Applications should not set ``V4L2_BUF_FLAG_REQUEST_FD`` for any ioctls
321 other than :ref:`VIDIOC_QBUF <VIDIOC_QBUF>`.
323 If the device does not support requests, then ``EACCES`` will be returned.
324 If requests are supported but an invalid request file descriptor is
325 given, then ``EINVAL`` will be returned.
329 .. c:type:: v4l2_plane
334 .. tabularcolumns:: |p{3.5cm}|p{3.5cm}|p{3.5cm}|p{7.0cm}|
336 .. cssclass:: longtable
346 - The number of bytes occupied by data in the plane (its payload).
347 Drivers must set this field when ``type`` refers to a capture
348 stream, applications when it refers to an output stream. If the
349 application sets this to 0 for an output stream, then
350 ``bytesused`` will be set to the size of the plane (see the
351 ``length`` field of this struct) by the driver.
355 Note that the actual image data starts at ``data_offset``
360 - Size in bytes of the plane (not its payload). This is set by the
361 driver based on the calls to
362 :ref:`VIDIOC_REQBUFS` and/or
363 :ref:`VIDIOC_CREATE_BUFS`.
371 - When the memory type in the containing struct
372 :c:type:`v4l2_buffer` is ``V4L2_MEMORY_MMAP``, this
373 is the value that should be passed to :ref:`mmap() <func-mmap>`,
374 similar to the ``offset`` field in struct
375 :c:type:`v4l2_buffer`.
379 - When the memory type in the containing struct
380 :c:type:`v4l2_buffer` is ``V4L2_MEMORY_USERPTR``,
381 this is a userspace pointer to the memory allocated for this plane
386 - When the memory type in the containing struct
387 :c:type:`v4l2_buffer` is ``V4L2_MEMORY_DMABUF``,
388 this is a file descriptor associated with a DMABUF buffer, similar
389 to the ``fd`` field in struct :c:type:`v4l2_buffer`.
393 - Offset in bytes to video data in the plane. Drivers must set this
394 field when ``type`` refers to a capture stream, applications when
395 it refers to an output stream.
399 That data_offset is included in ``bytesused``. So the
400 size of the image in the plane is ``bytesused``-``data_offset``
401 at offset ``data_offset`` from the start of the plane.
405 - Reserved for future use. Should be zeroed by drivers and
410 .. c:type:: v4l2_buf_type
415 .. cssclass:: longtable
417 .. tabularcolumns:: |p{7.2cm}|p{0.6cm}|p{9.7cm}|
424 * - ``V4L2_BUF_TYPE_VIDEO_CAPTURE``
426 - Buffer of a single-planar video capture stream, see
428 * - ``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE``
430 - Buffer of a multi-planar video capture stream, see
432 * - ``V4L2_BUF_TYPE_VIDEO_OUTPUT``
434 - Buffer of a single-planar video output stream, see
436 * - ``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE``
438 - Buffer of a multi-planar video output stream, see :ref:`output`.
439 * - ``V4L2_BUF_TYPE_VIDEO_OVERLAY``
441 - Buffer for video overlay, see :ref:`overlay`.
442 * - ``V4L2_BUF_TYPE_VBI_CAPTURE``
444 - Buffer of a raw VBI capture stream, see :ref:`raw-vbi`.
445 * - ``V4L2_BUF_TYPE_VBI_OUTPUT``
447 - Buffer of a raw VBI output stream, see :ref:`raw-vbi`.
448 * - ``V4L2_BUF_TYPE_SLICED_VBI_CAPTURE``
450 - Buffer of a sliced VBI capture stream, see :ref:`sliced`.
451 * - ``V4L2_BUF_TYPE_SLICED_VBI_OUTPUT``
453 - Buffer of a sliced VBI output stream, see :ref:`sliced`.
454 * - ``V4L2_BUF_TYPE_VIDEO_OUTPUT_OVERLAY``
456 - Buffer for video output overlay (OSD), see :ref:`osd`.
457 * - ``V4L2_BUF_TYPE_SDR_CAPTURE``
459 - Buffer for Software Defined Radio (SDR) capture stream, see
461 * - ``V4L2_BUF_TYPE_SDR_OUTPUT``
463 - Buffer for Software Defined Radio (SDR) output stream, see
465 * - ``V4L2_BUF_TYPE_META_CAPTURE``
467 - Buffer for metadata capture, see :ref:`metadata`.
476 .. tabularcolumns:: |p{7.0cm}|p{2.2cm}|p{8.3cm}|
478 .. cssclass:: longtable
485 * .. _`V4L2-BUF-FLAG-MAPPED`:
487 - ``V4L2_BUF_FLAG_MAPPED``
489 - The buffer resides in device memory and has been mapped into the
490 application's address space, see :ref:`mmap` for details.
491 Drivers set or clear this flag when the
492 :ref:`VIDIOC_QUERYBUF`,
493 :ref:`VIDIOC_QBUF` or
494 :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl is called. Set by the
496 * .. _`V4L2-BUF-FLAG-QUEUED`:
498 - ``V4L2_BUF_FLAG_QUEUED``
500 - Internally drivers maintain two buffer queues, an incoming and
501 outgoing queue. When this flag is set, the buffer is currently on
502 the incoming queue. It automatically moves to the outgoing queue
503 after the buffer has been filled (capture devices) or displayed
504 (output devices). Drivers set or clear this flag when the
505 ``VIDIOC_QUERYBUF`` ioctl is called. After (successful) calling
506 the ``VIDIOC_QBUF``\ ioctl it is always set and after
507 ``VIDIOC_DQBUF`` always cleared.
508 * .. _`V4L2-BUF-FLAG-DONE`:
510 - ``V4L2_BUF_FLAG_DONE``
512 - When this flag is set, the buffer is currently on the outgoing
513 queue, ready to be dequeued from the driver. Drivers set or clear
514 this flag when the ``VIDIOC_QUERYBUF`` ioctl is called. After
515 calling the ``VIDIOC_QBUF`` or ``VIDIOC_DQBUF`` it is always
516 cleared. Of course a buffer cannot be on both queues at the same
517 time, the ``V4L2_BUF_FLAG_QUEUED`` and ``V4L2_BUF_FLAG_DONE`` flag
518 are mutually exclusive. They can be both cleared however, then the
519 buffer is in "dequeued" state, in the application domain so to
521 * .. _`V4L2-BUF-FLAG-ERROR`:
523 - ``V4L2_BUF_FLAG_ERROR``
525 - When this flag is set, the buffer has been dequeued successfully,
526 although the data might have been corrupted. This is recoverable,
527 streaming may continue as normal and the buffer may be reused
528 normally. Drivers set this flag when the ``VIDIOC_DQBUF`` ioctl is
530 * .. _`V4L2-BUF-FLAG-IN-REQUEST`:
532 - ``V4L2_BUF_FLAG_IN_REQUEST``
534 - This buffer is part of a request that hasn't been queued yet.
535 * .. _`V4L2-BUF-FLAG-KEYFRAME`:
537 - ``V4L2_BUF_FLAG_KEYFRAME``
539 - Drivers set or clear this flag when calling the ``VIDIOC_DQBUF``
540 ioctl. It may be set by video capture devices when the buffer
541 contains a compressed image which is a key frame (or field), i. e.
542 can be decompressed on its own. Also known as an I-frame.
543 Applications can set this bit when ``type`` refers to an output
545 * .. _`V4L2-BUF-FLAG-PFRAME`:
547 - ``V4L2_BUF_FLAG_PFRAME``
549 - Similar to ``V4L2_BUF_FLAG_KEYFRAME`` this flags predicted frames
550 or fields which contain only differences to a previous key frame.
551 Applications can set this bit when ``type`` refers to an output
553 * .. _`V4L2-BUF-FLAG-BFRAME`:
555 - ``V4L2_BUF_FLAG_BFRAME``
557 - Similar to ``V4L2_BUF_FLAG_KEYFRAME`` this flags a bi-directional
558 predicted frame or field which contains only the differences
559 between the current frame and both the preceding and following key
560 frames to specify its content. Applications can set this bit when
561 ``type`` refers to an output stream.
562 * .. _`V4L2-BUF-FLAG-TIMECODE`:
564 - ``V4L2_BUF_FLAG_TIMECODE``
566 - The ``timecode`` field is valid. Drivers set or clear this flag
567 when the ``VIDIOC_DQBUF`` ioctl is called. Applications can set
568 this bit and the corresponding ``timecode`` structure when
569 ``type`` refers to an output stream.
570 * .. _`V4L2-BUF-FLAG-PREPARED`:
572 - ``V4L2_BUF_FLAG_PREPARED``
574 - The buffer has been prepared for I/O and can be queued by the
575 application. Drivers set or clear this flag when the
576 :ref:`VIDIOC_QUERYBUF`,
577 :ref:`VIDIOC_PREPARE_BUF <VIDIOC_QBUF>`,
578 :ref:`VIDIOC_QBUF` or
579 :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl is called.
580 * .. _`V4L2-BUF-FLAG-NO-CACHE-INVALIDATE`:
582 - ``V4L2_BUF_FLAG_NO_CACHE_INVALIDATE``
584 - Caches do not have to be invalidated for this buffer. Typically
585 applications shall use this flag if the data captured in the
586 buffer is not going to be touched by the CPU, instead the buffer
587 will, probably, be passed on to a DMA-capable hardware unit for
588 further processing or output.
589 * .. _`V4L2-BUF-FLAG-NO-CACHE-CLEAN`:
591 - ``V4L2_BUF_FLAG_NO_CACHE_CLEAN``
593 - Caches do not have to be cleaned for this buffer. Typically
594 applications shall use this flag for output buffers if the data in
595 this buffer has not been created by the CPU but by some
596 DMA-capable unit, in which case caches have not been used.
597 * .. _`V4L2-BUF-FLAG-LAST`:
599 - ``V4L2_BUF_FLAG_LAST``
601 - Last buffer produced by the hardware. mem2mem codec drivers set
602 this flag on the capture queue for the last buffer when the
603 :ref:`VIDIOC_QUERYBUF` or
604 :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl is called. Due to
605 hardware limitations, the last buffer may be empty. In this case
606 the driver will set the ``bytesused`` field to 0, regardless of
607 the format. Any Any subsequent call to the
608 :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl will not block anymore,
609 but return an ``EPIPE`` error code.
610 * .. _`V4L2-BUF-FLAG-REQUEST-FD`:
612 - ``V4L2_BUF_FLAG_REQUEST_FD``
614 - The ``request_fd`` field contains a valid file descriptor.
615 * .. _`V4L2-BUF-FLAG-TIMESTAMP-MASK`:
617 - ``V4L2_BUF_FLAG_TIMESTAMP_MASK``
619 - Mask for timestamp types below. To test the timestamp type, mask
620 out bits not belonging to timestamp type by performing a logical
621 and operation with buffer flags and timestamp mask.
622 * .. _`V4L2-BUF-FLAG-TIMESTAMP-UNKNOWN`:
624 - ``V4L2_BUF_FLAG_TIMESTAMP_UNKNOWN``
626 - Unknown timestamp type. This type is used by drivers before Linux
627 3.9 and may be either monotonic (see below) or realtime (wall
628 clock). Monotonic clock has been favoured in embedded systems
629 whereas most of the drivers use the realtime clock. Either kinds
630 of timestamps are available in user space via
631 :c:func:`clock_gettime` using clock IDs ``CLOCK_MONOTONIC``
632 and ``CLOCK_REALTIME``, respectively.
633 * .. _`V4L2-BUF-FLAG-TIMESTAMP-MONOTONIC`:
635 - ``V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC``
637 - The buffer timestamp has been taken from the ``CLOCK_MONOTONIC``
638 clock. To access the same clock outside V4L2, use
639 :c:func:`clock_gettime`.
640 * .. _`V4L2-BUF-FLAG-TIMESTAMP-COPY`:
642 - ``V4L2_BUF_FLAG_TIMESTAMP_COPY``
644 - The CAPTURE buffer timestamp has been taken from the corresponding
645 OUTPUT buffer. This flag applies only to mem2mem devices.
646 * .. _`V4L2-BUF-FLAG-TSTAMP-SRC-MASK`:
648 - ``V4L2_BUF_FLAG_TSTAMP_SRC_MASK``
650 - Mask for timestamp sources below. The timestamp source defines the
651 point of time the timestamp is taken in relation to the frame.
652 Logical 'and' operation between the ``flags`` field and
653 ``V4L2_BUF_FLAG_TSTAMP_SRC_MASK`` produces the value of the
654 timestamp source. Applications must set the timestamp source when
655 ``type`` refers to an output stream and
656 ``V4L2_BUF_FLAG_TIMESTAMP_COPY`` is set.
657 * .. _`V4L2-BUF-FLAG-TSTAMP-SRC-EOF`:
659 - ``V4L2_BUF_FLAG_TSTAMP_SRC_EOF``
661 - End Of Frame. The buffer timestamp has been taken when the last
662 pixel of the frame has been received or the last pixel of the
663 frame has been transmitted. In practice, software generated
664 timestamps will typically be read from the clock a small amount of
665 time after the last pixel has been received or transmitten,
666 depending on the system and other activity in it.
667 * .. _`V4L2-BUF-FLAG-TSTAMP-SRC-SOE`:
669 - ``V4L2_BUF_FLAG_TSTAMP_SRC_SOE``
671 - Start Of Exposure. The buffer timestamp has been taken when the
672 exposure of the frame has begun. This is only valid for the
673 ``V4L2_BUF_TYPE_VIDEO_CAPTURE`` buffer type.
677 .. c:type:: v4l2_memory
682 .. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|
689 * - ``V4L2_MEMORY_MMAP``
691 - The buffer is used for :ref:`memory mapping <mmap>` I/O.
692 * - ``V4L2_MEMORY_USERPTR``
694 - The buffer is used for :ref:`user pointer <userp>` I/O.
695 * - ``V4L2_MEMORY_OVERLAY``
698 * - ``V4L2_MEMORY_DMABUF``
700 - The buffer is used for :ref:`DMA shared buffer <dmabuf>` I/O.
707 The struct :c:type:`v4l2_timecode` structure is designed to hold a
708 :ref:`smpte12m` or similar timecode. (struct
709 struct :c:type:`timeval` timestamps are stored in struct
710 :c:type:`v4l2_buffer` field ``timestamp``.)
713 .. c:type:: v4l2_timecode
718 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
727 - Frame rate the timecodes are based on, see :ref:`timecode-type`.
730 - Timecode flags, see :ref:`timecode-flags`.
733 - Frame count, 0 ... 23/24/29/49/59, depending on the type of
737 - Seconds count, 0 ... 59. This is a binary, not BCD number.
740 - Minutes count, 0 ... 59. This is a binary, not BCD number.
743 - Hours count, 0 ... 29. This is a binary, not BCD number.
746 - The "user group" bits from the timecode.
755 .. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|
762 * - ``V4L2_TC_TYPE_24FPS``
764 - 24 frames per second, i. e. film.
765 * - ``V4L2_TC_TYPE_25FPS``
767 - 25 frames per second, i. e. PAL or SECAM video.
768 * - ``V4L2_TC_TYPE_30FPS``
770 - 30 frames per second, i. e. NTSC video.
771 * - ``V4L2_TC_TYPE_50FPS``
774 * - ``V4L2_TC_TYPE_60FPS``
785 .. tabularcolumns:: |p{6.6cm}|p{1.4cm}|p{9.5cm}|
792 * - ``V4L2_TC_FLAG_DROPFRAME``
794 - Indicates "drop frame" semantics for counting frames in 29.97 fps
795 material. When set, frame numbers 0 and 1 at the start of each
796 minute, except minutes 0, 10, 20, 30, 40, 50 are omitted from the
798 * - ``V4L2_TC_FLAG_COLORFRAME``
800 - The "color frame" flag.
801 * - ``V4L2_TC_USERBITS_field``
803 - Field mask for the "binary group flags".
804 * - ``V4L2_TC_USERBITS_USERDEFINED``
806 - Unspecified format.
807 * - ``V4L2_TC_USERBITS_8BITCHARS``
809 - 8-bit ISO characters.