1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2 3.. _buffer: 4 5******* 6Buffers 7******* 8 9A buffer contains data exchanged by application and driver using one of 10the Streaming I/O methods. In the multi-planar API, the data is held in 11planes, while the buffer structure acts as a container for the planes. 12Only pointers to buffers (planes) are exchanged, the data itself is not 13copied. These pointers, together with meta-information like timestamps 14or field parity, are stored in a struct :c:type:`v4l2_buffer`, 15argument to the :ref:`VIDIOC_QUERYBUF`, 16:ref:`VIDIOC_QBUF <VIDIOC_QBUF>` and 17:ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl. In the multi-planar API, 18some plane-specific members of struct :c:type:`v4l2_buffer`, 19such as pointers and sizes for each plane, are stored in 20struct :c:type:`v4l2_plane` instead. In that case, 21struct :c:type:`v4l2_buffer` contains an array of plane structures. 22 23Dequeued video buffers come with timestamps. The driver decides at which 24part of the frame and with which clock the timestamp is taken. Please 25see flags in the masks ``V4L2_BUF_FLAG_TIMESTAMP_MASK`` and 26``V4L2_BUF_FLAG_TSTAMP_SRC_MASK`` in :ref:`buffer-flags`. These flags 27are always valid and constant across all buffers during the whole video 28stream. 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 32mem-to-mem devices is an exception to the rule: the timestamp source 33flags are copied from the OUTPUT video buffer to the CAPTURE video 34buffer. 35 36 37Interactions between formats, controls and buffers 38================================================== 39 40V4L2 exposes parameters that influence the buffer size, or the way data is 41laid out in the buffer. Those parameters are exposed through both formats and 42controls. One example of such a control is the ``V4L2_CID_ROTATE`` control 43that modifies the direction in which pixels are stored in the buffer, as well 44as the buffer size when the selected format includes padding at the end of 45lines. 46 47The set of information needed to interpret the content of a buffer (e.g. the 48pixel format, the line stride, the tiling orientation or the rotation) is 49collectively referred to in the rest of this section as the buffer layout. 50 51Controls that can modify the buffer layout shall set the 52``V4L2_CTRL_FLAG_MODIFY_LAYOUT`` flag. 53 54Modifying formats or controls that influence the buffer size or layout require 55the stream to be stopped. Any attempt at such a modification while the stream 56is active shall cause the ioctl setting the format or the control to return 57the ``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 60control while the stream is active. 61 62.. note:: 63 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. 72 73Controls that only influence the buffer layout can be modified at any time 74when the stream is stopped. As they don't influence the buffer size, no 75special handling is needed to synchronize those controls with buffer 76allocation and the ``V4L2_CTRL_FLAG_GRABBED`` flag is cleared once the 77stream is stopped. 78 79Formats and controls that influence the buffer size interact with buffer 80allocation. The simplest way to handle this is for drivers to always require 81buffers to be reallocated in order to change those formats or controls. In 82that case, to perform such changes, userspace applications shall first stop 83the video stream with the :c:func:`VIDIOC_STREAMOFF` ioctl if it is running 84and free all buffers with the :c:func:`VIDIOC_REQBUFS` ioctl if they are 85allocated. After freeing all buffers the ``V4L2_CTRL_FLAG_GRABBED`` flag 86for controls is cleared. The format or controls can then be modified, and 87buffers shall then be reallocated and the stream restarted. A typical ioctl 88sequence is 89 90 #. VIDIOC_STREAMOFF 91 #. VIDIOC_REQBUFS(0) 92 #. VIDIOC_S_EXT_CTRLS 93 #. VIDIOC_S_FMT 94 #. VIDIOC_REQBUFS(n) 95 #. VIDIOC_QBUF 96 #. VIDIOC_STREAMON 97 98The second :c:func:`VIDIOC_REQBUFS` call will take the new format and control 99value into account to compute the buffer size to allocate. Applications can 100also retrieve the size by calling the :c:func:`VIDIOC_G_FMT` ioctl if needed. 101 102.. note:: 103 104 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. 109 110When reallocation is required, any attempt to modify format or controls that 111influences the buffer size while buffers are allocated shall cause the format 112or control set ioctl to return the ``EBUSY`` error. Any attempt to queue a 113buffer too small for the current format or controls shall cause the 114:c:func:`VIDIOC_QBUF` ioctl to return a ``EINVAL`` error. 115 116Buffer reallocation is an expensive operation. To avoid that cost, drivers can 117(and are encouraged to) allow format or controls that influence the buffer 118size to be changed with buffers allocated. In that case, a typical ioctl 119sequence to modify format and controls is 120 121 #. VIDIOC_STREAMOFF 122 #. VIDIOC_S_EXT_CTRLS 123 #. VIDIOC_S_FMT 124 #. VIDIOC_QBUF 125 #. VIDIOC_STREAMON 126 127For this sequence to operate correctly, queued buffers need to be large enough 128for the new format or controls. Drivers shall return a ``ENOSPC`` error in 129response 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 131for the new format are currently queued. As a simplification, drivers are 132allowed to return a ``EBUSY`` error from these ioctls if any buffer is 133currently queued, without checking the queued buffers sizes. 134 135Additionally, drivers shall return a ``EINVAL`` error from the 136:c:func:`VIDIOC_QBUF` ioctl if the buffer being queued is too small for the 137current format or controls. Together, these requirements ensure that queued 138buffers will always be large enough for the configured format and controls. 139 140Userspace applications can query the buffer size required for a given format 141and controls by first setting the desired control values and then trying the 142desired format. The :c:func:`VIDIOC_TRY_FMT` ioctl will return the required 143buffer size. 144 145 #. VIDIOC_S_EXT_CTRLS(x) 146 #. VIDIOC_TRY_FMT() 147 #. VIDIOC_S_EXT_CTRLS(y) 148 #. VIDIOC_TRY_FMT() 149 150The :c:func:`VIDIOC_CREATE_BUFS` ioctl can then be used to allocate buffers 151based on the queried sizes (for instance by allocating a set of buffers large 152enough for all the desired formats and controls, or by allocating separate set 153of appropriately sized buffers for each use case). 154 155 156.. c:type:: v4l2_buffer 157 158struct v4l2_buffer 159================== 160 161.. tabularcolumns:: |p{2.8cm}|p{2.5cm}|p{1.6cm}|p{10.2cm}| 162 163.. cssclass:: longtable 164 165.. flat-table:: struct v4l2_buffer 166 :header-rows: 0 167 :stub-columns: 0 168 :widths: 1 2 10 169 170 * - __u32 171 - ``index`` 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. 179 * - __u32 180 - ``type`` 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` 185 * - __u32 186 - ``bytesused`` 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. 196 * - __u32 197 - ``flags`` 198 - Flags set by the application or driver, see :ref:`buffer-flags`. 199 * - __u32 200 - ``field`` 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. 205 * - struct timeval 206 - ``timestamp`` 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 216 stream. 217 * - struct :c:type:`v4l2_timecode` 218 - ``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. 226 * - __u32 227 - ``sequence`` 228 - Set by the driver, counting the frames (not fields!) in sequence. 229 This field is set for both input and output devices. 230 * - :cspan:`2` 231 232 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 238 time. 239 240 .. note:: 241 242 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 246 :ref:`standard`. 247 248 * - __u32 249 - ``memory`` 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` 252 * - union { 253 - ``m`` 254 * - __u32 255 - ``offset`` 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 262 * - unsigned long 263 - ``userptr`` 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 269 - ``*planes`` 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. 274 * - int 275 - ``fd`` 276 - For the single-plane API and when ``memory`` is 277 ``V4L2_MEMORY_DMABUF`` this is the file descriptor associated with 278 a DMABUF buffer. 279 * - } 280 - 281 * - __u32 282 - ``length`` 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. 290 * - __u32 291 - ``reserved2`` 292 - A place holder for future extensions. Drivers and applications 293 must set this to 0. 294 * - __u32 295 - ``request_fd`` 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 299 be ignored. 300 301 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. 304 305 Applications should not set ``V4L2_BUF_FLAG_REQUEST_FD`` for any ioctls 306 other than :ref:`VIDIOC_QBUF <VIDIOC_QBUF>`. 307 308 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. 311 312 313 314.. c:type:: v4l2_plane 315 316struct v4l2_plane 317================= 318 319.. tabularcolumns:: |p{3.5cm}|p{3.5cm}|p{3.5cm}|p{7.0cm}| 320 321.. cssclass:: longtable 322 323.. flat-table:: 324 :header-rows: 0 325 :stub-columns: 0 326 :widths: 1 1 2 327 328 * - __u32 329 - ``bytesused`` 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. 336 337 .. note:: 338 339 Note that the actual image data starts at ``data_offset`` 340 which may not be 0. 341 * - __u32 342 - ``length`` 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`. 347 * - union { 348 - ``m`` 349 * - __u32 350 - ``mem_offset`` 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`. 356 * - unsigned long 357 - ``userptr`` 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 361 by an application. 362 * - int 363 - ``fd`` 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`. 368 * - } 369 - 370 * - __u32 371 - ``data_offset`` 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. 375 376 .. note:: 377 378 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. 381 * - __u32 382 - ``reserved[11]`` 383 - Reserved for future use. Should be zeroed by drivers and 384 applications. 385 386 387 388.. c:type:: v4l2_buf_type 389 390enum v4l2_buf_type 391================== 392 393.. cssclass:: longtable 394 395.. tabularcolumns:: |p{7.8cm}|p{0.6cm}|p{9.1cm}| 396 397.. flat-table:: 398 :header-rows: 0 399 :stub-columns: 0 400 :widths: 4 1 9 401 402 * - ``V4L2_BUF_TYPE_VIDEO_CAPTURE`` 403 - 1 404 - Buffer of a single-planar video capture stream, see 405 :ref:`capture`. 406 * - ``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE`` 407 - 9 408 - Buffer of a multi-planar video capture stream, see 409 :ref:`capture`. 410 * - ``V4L2_BUF_TYPE_VIDEO_OUTPUT`` 411 - 2 412 - Buffer of a single-planar video output stream, see 413 :ref:`output`. 414 * - ``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE`` 415 - 10 416 - Buffer of a multi-planar video output stream, see :ref:`output`. 417 * - ``V4L2_BUF_TYPE_VIDEO_OVERLAY`` 418 - 3 419 - Buffer for video overlay, see :ref:`overlay`. 420 * - ``V4L2_BUF_TYPE_VBI_CAPTURE`` 421 - 4 422 - Buffer of a raw VBI capture stream, see :ref:`raw-vbi`. 423 * - ``V4L2_BUF_TYPE_VBI_OUTPUT`` 424 - 5 425 - Buffer of a raw VBI output stream, see :ref:`raw-vbi`. 426 * - ``V4L2_BUF_TYPE_SLICED_VBI_CAPTURE`` 427 - 6 428 - Buffer of a sliced VBI capture stream, see :ref:`sliced`. 429 * - ``V4L2_BUF_TYPE_SLICED_VBI_OUTPUT`` 430 - 7 431 - Buffer of a sliced VBI output stream, see :ref:`sliced`. 432 * - ``V4L2_BUF_TYPE_VIDEO_OUTPUT_OVERLAY`` 433 - 8 434 - Buffer for video output overlay (OSD), see :ref:`osd`. 435 * - ``V4L2_BUF_TYPE_SDR_CAPTURE`` 436 - 11 437 - Buffer for Software Defined Radio (SDR) capture stream, see 438 :ref:`sdr`. 439 * - ``V4L2_BUF_TYPE_SDR_OUTPUT`` 440 - 12 441 - Buffer for Software Defined Radio (SDR) output stream, see 442 :ref:`sdr`. 443 * - ``V4L2_BUF_TYPE_META_CAPTURE`` 444 - 13 445 - Buffer for metadata capture, see :ref:`metadata`. 446 * - ``V4L2_BUF_TYPE_META_OUTPUT`` 447 - 14 448 - Buffer for metadata output, see :ref:`metadata`. 449 450 451 452.. _buffer-flags: 453 454Buffer Flags 455============ 456 457.. raw:: latex 458 459 \small 460 461.. tabularcolumns:: |p{7.0cm}|p{2.1cm}|p{8.4cm}| 462 463.. cssclass:: longtable 464 465.. flat-table:: 466 :header-rows: 0 467 :stub-columns: 0 468 :widths: 3 1 4 469 470 * .. _`V4L2-BUF-FLAG-MAPPED`: 471 472 - ``V4L2_BUF_FLAG_MAPPED`` 473 - 0x00000001 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 480 driver. 481 * .. _`V4L2-BUF-FLAG-QUEUED`: 482 483 - ``V4L2_BUF_FLAG_QUEUED`` 484 - 0x00000002 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`: 494 495 - ``V4L2_BUF_FLAG_DONE`` 496 - 0x00000004 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 505 say. 506 * .. _`V4L2-BUF-FLAG-ERROR`: 507 508 - ``V4L2_BUF_FLAG_ERROR`` 509 - 0x00000040 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 514 called. 515 * .. _`V4L2-BUF-FLAG-IN-REQUEST`: 516 517 - ``V4L2_BUF_FLAG_IN_REQUEST`` 518 - 0x00000080 519 - This buffer is part of a request that hasn't been queued yet. 520 * .. _`V4L2-BUF-FLAG-KEYFRAME`: 521 522 - ``V4L2_BUF_FLAG_KEYFRAME`` 523 - 0x00000008 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 529 stream. 530 * .. _`V4L2-BUF-FLAG-PFRAME`: 531 532 - ``V4L2_BUF_FLAG_PFRAME`` 533 - 0x00000010 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 537 stream. 538 * .. _`V4L2-BUF-FLAG-BFRAME`: 539 540 - ``V4L2_BUF_FLAG_BFRAME`` 541 - 0x00000020 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`: 548 549 - ``V4L2_BUF_FLAG_TIMECODE`` 550 - 0x00000100 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`: 556 557 - ``V4L2_BUF_FLAG_PREPARED`` 558 - 0x00000400 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`: 566 567 - ``V4L2_BUF_FLAG_NO_CACHE_INVALIDATE`` 568 - 0x00000800 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`: 578 579 - ``V4L2_BUF_FLAG_NO_CACHE_CLEAN`` 580 - 0x00001000 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`: 589 590 - ``V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF`` 591 - 0x00000200 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`: 602 603 - ``V4L2_BUF_FLAG_LAST`` 604 - 0x00100000 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`: 615 616 - ``V4L2_BUF_FLAG_REQUEST_FD`` 617 - 0x00800000 618 - The ``request_fd`` field contains a valid file descriptor. 619 * .. _`V4L2-BUF-FLAG-TIMESTAMP-MASK`: 620 621 - ``V4L2_BUF_FLAG_TIMESTAMP_MASK`` 622 - 0x0000e000 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`: 627 628 - ``V4L2_BUF_FLAG_TIMESTAMP_UNKNOWN`` 629 - 0x00000000 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`: 638 639 - ``V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC`` 640 - 0x00002000 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`: 645 646 - ``V4L2_BUF_FLAG_TIMESTAMP_COPY`` 647 - 0x00004000 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`: 651 652 - ``V4L2_BUF_FLAG_TSTAMP_SRC_MASK`` 653 - 0x00070000 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`: 662 663 - ``V4L2_BUF_FLAG_TSTAMP_SRC_EOF`` 664 - 0x00000000 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`: 672 673 - ``V4L2_BUF_FLAG_TSTAMP_SRC_SOE`` 674 - 0x00010000 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. 678 679.. raw:: latex 680 681 \normalsize 682 683.. _memory-flags: 684 685Memory Consistency Flags 686======================== 687 688.. tabularcolumns:: |p{7.0cm}|p{2.2cm}|p{8.3cm}| 689 690.. cssclass:: longtable 691 692.. flat-table:: 693 :header-rows: 0 694 :stub-columns: 0 695 :widths: 3 1 4 696 697.. c:type:: v4l2_memory 698 699enum v4l2_memory 700================ 701 702.. tabularcolumns:: |p{5.0cm}|p{0.8cm}|p{11.7cm}| 703 704.. flat-table:: 705 :header-rows: 0 706 :stub-columns: 0 707 :widths: 3 1 4 708 709 * - ``V4L2_MEMORY_MMAP`` 710 - 1 711 - The buffer is used for :ref:`memory mapping <mmap>` I/O. 712 * - ``V4L2_MEMORY_USERPTR`` 713 - 2 714 - The buffer is used for :ref:`user pointer <userp>` I/O. 715 * - ``V4L2_MEMORY_OVERLAY`` 716 - 3 717 - [to do] 718 * - ``V4L2_MEMORY_DMABUF`` 719 - 4 720 - The buffer is used for :ref:`DMA shared buffer <dmabuf>` I/O. 721 722 723 724Timecodes 725========= 726 727The :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.) 731 732 733.. c:type:: v4l2_timecode 734 735struct v4l2_timecode 736-------------------- 737 738.. tabularcolumns:: |p{1.4cm}|p{2.8cm}|p{12.3cm}| 739 740.. flat-table:: 741 :header-rows: 0 742 :stub-columns: 0 743 :widths: 1 1 2 744 745 * - __u32 746 - ``type`` 747 - Frame rate the timecodes are based on, see :ref:`timecode-type`. 748 * - __u32 749 - ``flags`` 750 - Timecode flags, see :ref:`timecode-flags`. 751 * - __u8 752 - ``frames`` 753 - Frame count, 0 ... 23/24/29/49/59, depending on the type of 754 timecode. 755 * - __u8 756 - ``seconds`` 757 - Seconds count, 0 ... 59. This is a binary, not BCD number. 758 * - __u8 759 - ``minutes`` 760 - Minutes count, 0 ... 59. This is a binary, not BCD number. 761 * - __u8 762 - ``hours`` 763 - Hours count, 0 ... 29. This is a binary, not BCD number. 764 * - __u8 765 - ``userbits``\ [4] 766 - The "user group" bits from the timecode. 767 768 769 770.. _timecode-type: 771 772Timecode Types 773-------------- 774 775.. tabularcolumns:: |p{5.6cm}|p{0.8cm}|p{11.1cm}| 776 777.. flat-table:: 778 :header-rows: 0 779 :stub-columns: 0 780 :widths: 3 1 4 781 782 * - ``V4L2_TC_TYPE_24FPS`` 783 - 1 784 - 24 frames per second, i. e. film. 785 * - ``V4L2_TC_TYPE_25FPS`` 786 - 2 787 - 25 frames per second, i. e. PAL or SECAM video. 788 * - ``V4L2_TC_TYPE_30FPS`` 789 - 3 790 - 30 frames per second, i. e. NTSC video. 791 * - ``V4L2_TC_TYPE_50FPS`` 792 - 4 793 - 794 * - ``V4L2_TC_TYPE_60FPS`` 795 - 5 796 - 797 798 799 800.. _timecode-flags: 801 802Timecode Flags 803-------------- 804 805.. tabularcolumns:: |p{6.6cm}|p{1.4cm}|p{9.5cm}| 806 807.. flat-table:: 808 :header-rows: 0 809 :stub-columns: 0 810 :widths: 3 1 4 811 812 * - ``V4L2_TC_FLAG_DROPFRAME`` 813 - 0x0001 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 817 count. 818 * - ``V4L2_TC_FLAG_COLORFRAME`` 819 - 0x0002 820 - The "color frame" flag. 821 * - ``V4L2_TC_USERBITS_field`` 822 - 0x000C 823 - Field mask for the "binary group flags". 824 * - ``V4L2_TC_USERBITS_USERDEFINED`` 825 - 0x0000 826 - Unspecified format. 827 * - ``V4L2_TC_USERBITS_8BITCHARS`` 828 - 0x0008 829 - 8-bit ISO characters. 830