1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
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
20 struct :c:type:`v4l2_plane` instead. In that case,
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{1.6cm}|p{10.2cm}|
163 .. cssclass:: longtable
165 .. flat-table:: struct v4l2_buffer
172 - Number of the buffer, set by the application except when calling
173 :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>`, then it is set by the
174 driver. This field can range from zero to the number of buffers
175 allocated with the :ref:`VIDIOC_REQBUFS` ioctl
176 (struct :c:type:`v4l2_requestbuffers`
177 ``count``), plus any buffers allocated with
178 :ref:`VIDIOC_CREATE_BUFS` minus one.
181 - Type of the buffer, same as struct
182 :c:type:`v4l2_format` ``type`` or struct
183 :c:type:`v4l2_requestbuffers` ``type``, set
184 by the application. See :c:type:`v4l2_buf_type`
187 - The number of bytes occupied by the data in the buffer. It depends
188 on the negotiated data format and may change with each buffer for
189 compressed variable size data like JPEG images. Drivers must set
190 this field when ``type`` refers to a capture stream, applications
191 when it refers to an output stream. If the application sets this
192 to 0 for an output stream, then ``bytesused`` will be set to the
193 size of the buffer (see the ``length`` field of this struct) by
194 the driver. For multiplanar formats this field is ignored and the
195 ``planes`` pointer is used instead.
198 - Flags set by the application or driver, see :ref:`buffer-flags`.
201 - Indicates the field order of the image in the buffer, see
202 :c:type:`v4l2_field`. This field is not used when the buffer
203 contains VBI data. Drivers must set it when ``type`` refers to a
204 capture stream, applications when it refers to an output stream.
207 - For capture streams this is time when the first data byte was
208 captured, as returned by the :c:func:`clock_gettime()` function
209 for the relevant clock id; see ``V4L2_BUF_FLAG_TIMESTAMP_*`` in
210 :ref:`buffer-flags`. For output streams the driver stores the
211 time at which the last data byte was actually sent out in the
212 ``timestamp`` field. This permits applications to monitor the
213 drift between the video and system clock. For output streams that
214 use ``V4L2_BUF_FLAG_TIMESTAMP_COPY`` the application has to fill
215 in the timestamp which will be copied by the driver to the capture
217 * - struct :c:type:`v4l2_timecode`
219 - When the ``V4L2_BUF_FLAG_TIMECODE`` flag is set in ``flags``, this
220 structure contains a frame timecode. In
221 :c:type:`V4L2_FIELD_ALTERNATE <v4l2_field>` mode the top and
222 bottom field contain the same timecode. Timecodes are intended to
223 help video editing and are typically recorded on video tapes, but
224 also embedded in compressed formats like MPEG. This field is
225 independent of the ``timestamp`` and ``sequence`` fields.
228 - Set by the driver, counting the frames (not fields!) in sequence.
229 This field is set for both input and output devices.
232 In :c:type:`V4L2_FIELD_ALTERNATE <v4l2_field>` mode the top and
233 bottom field have the same sequence number. The count starts at
234 zero and includes dropped or repeated frames. A dropped frame was
235 received by an input device but could not be stored due to lack of
236 free buffer space. A repeated frame was displayed again by an
237 output device because the application did not pass new data in
242 This may count the frames received e.g. over USB, without
243 taking into account the frames dropped by the remote hardware due
244 to limited compression throughput or bus bandwidth. These devices
245 identify by not enumerating any video standards, see
250 - This field must be set by applications and/or drivers in
251 accordance with the selected I/O method. See :c:type:`v4l2_memory`
256 - For the single-planar API and when ``memory`` is
257 ``V4L2_MEMORY_MMAP`` this is the offset of the buffer from the
258 start of the device memory. The value is returned by the driver
259 and apart of serving as parameter to the
260 :ref:`mmap() <func-mmap>` function not useful for applications.
261 See :ref:`mmap` for details
264 - For the single-planar API and when ``memory`` is
265 ``V4L2_MEMORY_USERPTR`` this is a pointer to the buffer (casted to
266 unsigned long type) in virtual memory, set by the application. See
267 :ref:`userp` for details.
268 * - struct v4l2_plane
270 - When using the multi-planar API, contains a userspace pointer to
271 an array of struct :c:type:`v4l2_plane`. The size of
272 the array should be put in the ``length`` field of this
273 struct :c:type:`v4l2_buffer` structure.
276 - For the single-plane API and when ``memory`` is
277 ``V4L2_MEMORY_DMABUF`` this is the file descriptor associated with
283 - Size of the buffer (not the payload) in bytes for the
284 single-planar API. This is set by the driver based on the calls to
285 :ref:`VIDIOC_REQBUFS` and/or
286 :ref:`VIDIOC_CREATE_BUFS`. For the
287 multi-planar API the application sets this to the number of
288 elements in the ``planes`` array. The driver will fill in the
289 actual number of valid elements in that array.
292 - A place holder for future extensions. Drivers and applications
296 - The file descriptor of the request to queue the buffer to. If the flag
297 ``V4L2_BUF_FLAG_REQUEST_FD`` is set, then the buffer will be
298 queued to this request. If the flag is not set, then this field will
301 The ``V4L2_BUF_FLAG_REQUEST_FD`` flag and this field are only used by
302 :ref:`ioctl VIDIOC_QBUF <VIDIOC_QBUF>` and ignored by other ioctls that
303 take a :c:type:`v4l2_buffer` as argument.
305 Applications should not set ``V4L2_BUF_FLAG_REQUEST_FD`` for any ioctls
306 other than :ref:`VIDIOC_QBUF <VIDIOC_QBUF>`.
308 If the device does not support requests, then ``EBADR`` will be returned.
309 If requests are supported but an invalid request file descriptor is
310 given, then ``EINVAL`` will be returned.
314 .. c:type:: v4l2_plane
319 .. tabularcolumns:: |p{3.5cm}|p{3.5cm}|p{3.5cm}|p{7.0cm}|
321 .. cssclass:: longtable
330 - The number of bytes occupied by data in the plane (its payload).
331 Drivers must set this field when ``type`` refers to a capture
332 stream, applications when it refers to an output stream. If the
333 application sets this to 0 for an output stream, then
334 ``bytesused`` will be set to the size of the plane (see the
335 ``length`` field of this struct) by the driver.
339 Note that the actual image data starts at ``data_offset``
343 - Size in bytes of the plane (not its payload). This is set by the
344 driver based on the calls to
345 :ref:`VIDIOC_REQBUFS` and/or
346 :ref:`VIDIOC_CREATE_BUFS`.
351 - When the memory type in the containing struct
352 :c:type:`v4l2_buffer` is ``V4L2_MEMORY_MMAP``, this
353 is the value that should be passed to :ref:`mmap() <func-mmap>`,
354 similar to the ``offset`` field in struct
355 :c:type:`v4l2_buffer`.
358 - When the memory type in the containing struct
359 :c:type:`v4l2_buffer` is ``V4L2_MEMORY_USERPTR``,
360 this is a userspace pointer to the memory allocated for this plane
364 - When the memory type in the containing struct
365 :c:type:`v4l2_buffer` is ``V4L2_MEMORY_DMABUF``,
366 this is a file descriptor associated with a DMABUF buffer, similar
367 to the ``fd`` field in struct :c:type:`v4l2_buffer`.
372 - Offset in bytes to video data in the plane. Drivers must set this
373 field when ``type`` refers to a capture stream, applications when
374 it refers to an output stream.
378 That data_offset is included in ``bytesused``. So the
379 size of the image in the plane is ``bytesused``-``data_offset``
380 at offset ``data_offset`` from the start of the plane.
383 - Reserved for future use. Should be zeroed by drivers and
388 .. c:type:: v4l2_buf_type
393 .. cssclass:: longtable
395 .. tabularcolumns:: |p{7.8cm}|p{0.6cm}|p{9.1cm}|
402 * - ``V4L2_BUF_TYPE_VIDEO_CAPTURE``
404 - Buffer of a single-planar video capture stream, see
406 * - ``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE``
408 - Buffer of a multi-planar video capture stream, see
410 * - ``V4L2_BUF_TYPE_VIDEO_OUTPUT``
412 - Buffer of a single-planar video output stream, see
414 * - ``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE``
416 - Buffer of a multi-planar video output stream, see :ref:`output`.
417 * - ``V4L2_BUF_TYPE_VIDEO_OVERLAY``
419 - Buffer for video overlay, see :ref:`overlay`.
420 * - ``V4L2_BUF_TYPE_VBI_CAPTURE``
422 - Buffer of a raw VBI capture stream, see :ref:`raw-vbi`.
423 * - ``V4L2_BUF_TYPE_VBI_OUTPUT``
425 - Buffer of a raw VBI output stream, see :ref:`raw-vbi`.
426 * - ``V4L2_BUF_TYPE_SLICED_VBI_CAPTURE``
428 - Buffer of a sliced VBI capture stream, see :ref:`sliced`.
429 * - ``V4L2_BUF_TYPE_SLICED_VBI_OUTPUT``
431 - Buffer of a sliced VBI output stream, see :ref:`sliced`.
432 * - ``V4L2_BUF_TYPE_VIDEO_OUTPUT_OVERLAY``
434 - Buffer for video output overlay (OSD), see :ref:`osd`.
435 * - ``V4L2_BUF_TYPE_SDR_CAPTURE``
437 - Buffer for Software Defined Radio (SDR) capture stream, see
439 * - ``V4L2_BUF_TYPE_SDR_OUTPUT``
441 - Buffer for Software Defined Radio (SDR) output stream, see
443 * - ``V4L2_BUF_TYPE_META_CAPTURE``
445 - Buffer for metadata capture, see :ref:`metadata`.
446 * - ``V4L2_BUF_TYPE_META_OUTPUT``
448 - Buffer for metadata output, see :ref:`metadata`.
461 .. tabularcolumns:: |p{7.0cm}|p{2.1cm}|p{8.4cm}|
463 .. cssclass:: longtable
470 * .. _`V4L2-BUF-FLAG-MAPPED`:
472 - ``V4L2_BUF_FLAG_MAPPED``
474 - The buffer resides in device memory and has been mapped into the
475 application's address space, see :ref:`mmap` for details.
476 Drivers set or clear this flag when the
477 :ref:`VIDIOC_QUERYBUF`,
478 :ref:`VIDIOC_QBUF` or
479 :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl is called. Set by the
481 * .. _`V4L2-BUF-FLAG-QUEUED`:
483 - ``V4L2_BUF_FLAG_QUEUED``
485 - Internally drivers maintain two buffer queues, an incoming and
486 outgoing queue. When this flag is set, the buffer is currently on
487 the incoming queue. It automatically moves to the outgoing queue
488 after the buffer has been filled (capture devices) or displayed
489 (output devices). Drivers set or clear this flag when the
490 ``VIDIOC_QUERYBUF`` ioctl is called. After (successful) calling
491 the ``VIDIOC_QBUF``\ ioctl it is always set and after
492 ``VIDIOC_DQBUF`` always cleared.
493 * .. _`V4L2-BUF-FLAG-DONE`:
495 - ``V4L2_BUF_FLAG_DONE``
497 - When this flag is set, the buffer is currently on the outgoing
498 queue, ready to be dequeued from the driver. Drivers set or clear
499 this flag when the ``VIDIOC_QUERYBUF`` ioctl is called. After
500 calling the ``VIDIOC_QBUF`` or ``VIDIOC_DQBUF`` it is always
501 cleared. Of course a buffer cannot be on both queues at the same
502 time, the ``V4L2_BUF_FLAG_QUEUED`` and ``V4L2_BUF_FLAG_DONE`` flag
503 are mutually exclusive. They can be both cleared however, then the
504 buffer is in "dequeued" state, in the application domain so to
506 * .. _`V4L2-BUF-FLAG-ERROR`:
508 - ``V4L2_BUF_FLAG_ERROR``
510 - When this flag is set, the buffer has been dequeued successfully,
511 although the data might have been corrupted. This is recoverable,
512 streaming may continue as normal and the buffer may be reused
513 normally. Drivers set this flag when the ``VIDIOC_DQBUF`` ioctl is
515 * .. _`V4L2-BUF-FLAG-IN-REQUEST`:
517 - ``V4L2_BUF_FLAG_IN_REQUEST``
519 - This buffer is part of a request that hasn't been queued yet.
520 * .. _`V4L2-BUF-FLAG-KEYFRAME`:
522 - ``V4L2_BUF_FLAG_KEYFRAME``
524 - Drivers set or clear this flag when calling the ``VIDIOC_DQBUF``
525 ioctl. It may be set by video capture devices when the buffer
526 contains a compressed image which is a key frame (or field), i. e.
527 can be decompressed on its own. Also known as an I-frame.
528 Applications can set this bit when ``type`` refers to an output
530 * .. _`V4L2-BUF-FLAG-PFRAME`:
532 - ``V4L2_BUF_FLAG_PFRAME``
534 - Similar to ``V4L2_BUF_FLAG_KEYFRAME`` this flags predicted frames
535 or fields which contain only differences to a previous key frame.
536 Applications can set this bit when ``type`` refers to an output
538 * .. _`V4L2-BUF-FLAG-BFRAME`:
540 - ``V4L2_BUF_FLAG_BFRAME``
542 - Similar to ``V4L2_BUF_FLAG_KEYFRAME`` this flags a bi-directional
543 predicted frame or field which contains only the differences
544 between the current frame and both the preceding and following key
545 frames to specify its content. Applications can set this bit when
546 ``type`` refers to an output stream.
547 * .. _`V4L2-BUF-FLAG-TIMECODE`:
549 - ``V4L2_BUF_FLAG_TIMECODE``
551 - The ``timecode`` field is valid. Drivers set or clear this flag
552 when the ``VIDIOC_DQBUF`` ioctl is called. Applications can set
553 this bit and the corresponding ``timecode`` structure when
554 ``type`` refers to an output stream.
555 * .. _`V4L2-BUF-FLAG-PREPARED`:
557 - ``V4L2_BUF_FLAG_PREPARED``
559 - The buffer has been prepared for I/O and can be queued by the
560 application. Drivers set or clear this flag when the
561 :ref:`VIDIOC_QUERYBUF`,
562 :ref:`VIDIOC_PREPARE_BUF <VIDIOC_QBUF>`,
563 :ref:`VIDIOC_QBUF` or
564 :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl is called.
565 * .. _`V4L2-BUF-FLAG-NO-CACHE-INVALIDATE`:
567 - ``V4L2_BUF_FLAG_NO_CACHE_INVALIDATE``
569 - Caches do not have to be invalidated for this buffer. Typically
570 applications shall use this flag if the data captured in the
571 buffer is not going to be touched by the CPU, instead the buffer
572 will, probably, be passed on to a DMA-capable hardware unit for
573 further processing or output. This flag is ignored unless the
574 queue is used for :ref:`memory mapping <mmap>` streaming I/O and
575 reports :ref:`V4L2_BUF_CAP_SUPPORTS_MMAP_CACHE_HINTS
576 <V4L2-BUF-CAP-SUPPORTS-MMAP-CACHE-HINTS>` capability.
577 * .. _`V4L2-BUF-FLAG-NO-CACHE-CLEAN`:
579 - ``V4L2_BUF_FLAG_NO_CACHE_CLEAN``
581 - Caches do not have to be cleaned for this buffer. Typically
582 applications shall use this flag for output buffers if the data in
583 this buffer has not been created by the CPU but by some
584 DMA-capable unit, in which case caches have not been used. This flag
585 is ignored unless the queue is used for :ref:`memory mapping <mmap>`
586 streaming I/O and reports :ref:`V4L2_BUF_CAP_SUPPORTS_MMAP_CACHE_HINTS
587 <V4L2-BUF-CAP-SUPPORTS-MMAP-CACHE-HINTS>` capability.
588 * .. _`V4L2-BUF-FLAG-M2M-HOLD-CAPTURE-BUF`:
590 - ``V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF``
592 - Only valid if ``V4L2_BUF_CAP_SUPPORTS_M2M_HOLD_CAPTURE_BUF`` is
593 set. It is typically used with stateless decoders where multiple
594 output buffers each decode to a slice of the decoded frame.
595 Applications can set this flag when queueing the output buffer
596 to prevent the driver from dequeueing the capture buffer after
597 the output buffer has been decoded (i.e. the capture buffer is
598 'held'). If the timestamp of this output buffer differs from that
599 of the previous output buffer, then that indicates the start of a
600 new frame and the previously held capture buffer is dequeued.
601 * .. _`V4L2-BUF-FLAG-LAST`:
603 - ``V4L2_BUF_FLAG_LAST``
605 - Last buffer produced by the hardware. mem2mem codec drivers set
606 this flag on the capture queue for the last buffer when the
607 :ref:`VIDIOC_QUERYBUF` or
608 :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl is called. Due to
609 hardware limitations, the last buffer may be empty. In this case
610 the driver will set the ``bytesused`` field to 0, regardless of
611 the format. Any Any subsequent call to the
612 :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl will not block anymore,
613 but return an ``EPIPE`` error code.
614 * .. _`V4L2-BUF-FLAG-REQUEST-FD`:
616 - ``V4L2_BUF_FLAG_REQUEST_FD``
618 - The ``request_fd`` field contains a valid file descriptor.
619 * .. _`V4L2-BUF-FLAG-TIMESTAMP-MASK`:
621 - ``V4L2_BUF_FLAG_TIMESTAMP_MASK``
623 - Mask for timestamp types below. To test the timestamp type, mask
624 out bits not belonging to timestamp type by performing a logical
625 and operation with buffer flags and timestamp mask.
626 * .. _`V4L2-BUF-FLAG-TIMESTAMP-UNKNOWN`:
628 - ``V4L2_BUF_FLAG_TIMESTAMP_UNKNOWN``
630 - Unknown timestamp type. This type is used by drivers before Linux
631 3.9 and may be either monotonic (see below) or realtime (wall
632 clock). Monotonic clock has been favoured in embedded systems
633 whereas most of the drivers use the realtime clock. Either kinds
634 of timestamps are available in user space via
635 :c:func:`clock_gettime` using clock IDs ``CLOCK_MONOTONIC``
636 and ``CLOCK_REALTIME``, respectively.
637 * .. _`V4L2-BUF-FLAG-TIMESTAMP-MONOTONIC`:
639 - ``V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC``
641 - The buffer timestamp has been taken from the ``CLOCK_MONOTONIC``
642 clock. To access the same clock outside V4L2, use
643 :c:func:`clock_gettime`.
644 * .. _`V4L2-BUF-FLAG-TIMESTAMP-COPY`:
646 - ``V4L2_BUF_FLAG_TIMESTAMP_COPY``
648 - The CAPTURE buffer timestamp has been taken from the corresponding
649 OUTPUT buffer. This flag applies only to mem2mem devices.
650 * .. _`V4L2-BUF-FLAG-TSTAMP-SRC-MASK`:
652 - ``V4L2_BUF_FLAG_TSTAMP_SRC_MASK``
654 - Mask for timestamp sources below. The timestamp source defines the
655 point of time the timestamp is taken in relation to the frame.
656 Logical 'and' operation between the ``flags`` field and
657 ``V4L2_BUF_FLAG_TSTAMP_SRC_MASK`` produces the value of the
658 timestamp source. Applications must set the timestamp source when
659 ``type`` refers to an output stream and
660 ``V4L2_BUF_FLAG_TIMESTAMP_COPY`` is set.
661 * .. _`V4L2-BUF-FLAG-TSTAMP-SRC-EOF`:
663 - ``V4L2_BUF_FLAG_TSTAMP_SRC_EOF``
665 - End Of Frame. The buffer timestamp has been taken when the last
666 pixel of the frame has been received or the last pixel of the
667 frame has been transmitted. In practice, software generated
668 timestamps will typically be read from the clock a small amount of
669 time after the last pixel has been received or transmitten,
670 depending on the system and other activity in it.
671 * .. _`V4L2-BUF-FLAG-TSTAMP-SRC-SOE`:
673 - ``V4L2_BUF_FLAG_TSTAMP_SRC_SOE``
675 - Start Of Exposure. The buffer timestamp has been taken when the
676 exposure of the frame has begun. This is only valid for the
677 ``V4L2_BUF_TYPE_VIDEO_CAPTURE`` buffer type.
685 Memory Consistency Flags
686 ========================
688 .. tabularcolumns:: |p{7.0cm}|p{2.2cm}|p{8.3cm}|
690 .. cssclass:: longtable
697 .. c:type:: v4l2_memory
702 .. tabularcolumns:: |p{5.0cm}|p{0.8cm}|p{11.7cm}|
709 * - ``V4L2_MEMORY_MMAP``
711 - The buffer is used for :ref:`memory mapping <mmap>` I/O.
712 * - ``V4L2_MEMORY_USERPTR``
714 - The buffer is used for :ref:`user pointer <userp>` I/O.
715 * - ``V4L2_MEMORY_OVERLAY``
718 * - ``V4L2_MEMORY_DMABUF``
720 - The buffer is used for :ref:`DMA shared buffer <dmabuf>` I/O.
727 The :c:type:`v4l2_buffer_timecode` structure is designed to hold a
728 :ref:`smpte12m` or similar timecode.
729 (struct :c:type:`timeval` timestamps are stored in the struct
730 :c:type:`v4l2_buffer` ``timestamp`` field.)
733 .. c:type:: v4l2_timecode
738 .. tabularcolumns:: |p{1.4cm}|p{2.8cm}|p{12.3cm}|
747 - Frame rate the timecodes are based on, see :ref:`timecode-type`.
750 - Timecode flags, see :ref:`timecode-flags`.
753 - Frame count, 0 ... 23/24/29/49/59, depending on the type of
757 - Seconds count, 0 ... 59. This is a binary, not BCD number.
760 - Minutes count, 0 ... 59. This is a binary, not BCD number.
763 - Hours count, 0 ... 29. This is a binary, not BCD number.
766 - The "user group" bits from the timecode.
775 .. tabularcolumns:: |p{5.6cm}|p{0.8cm}|p{11.1cm}|
782 * - ``V4L2_TC_TYPE_24FPS``
784 - 24 frames per second, i. e. film.
785 * - ``V4L2_TC_TYPE_25FPS``
787 - 25 frames per second, i. e. PAL or SECAM video.
788 * - ``V4L2_TC_TYPE_30FPS``
790 - 30 frames per second, i. e. NTSC video.
791 * - ``V4L2_TC_TYPE_50FPS``
794 * - ``V4L2_TC_TYPE_60FPS``
805 .. tabularcolumns:: |p{6.6cm}|p{1.4cm}|p{9.5cm}|
812 * - ``V4L2_TC_FLAG_DROPFRAME``
814 - Indicates "drop frame" semantics for counting frames in 29.97 fps
815 material. When set, frame numbers 0 and 1 at the start of each
816 minute, except minutes 0, 10, 20, 30, 40, 50 are omitted from the
818 * - ``V4L2_TC_FLAG_COLORFRAME``
820 - The "color frame" flag.
821 * - ``V4L2_TC_USERBITS_field``
823 - Field mask for the "binary group flags".
824 * - ``V4L2_TC_USERBITS_USERDEFINED``
826 - Unspecified format.
827 * - ``V4L2_TC_USERBITS_8BITCHARS``
829 - 8-bit ISO characters.