1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2.. c:namespace:: V4L 3 4.. _buffer: 5 6******* 7Buffers 8******* 9 10A buffer contains data exchanged by application and driver using one of 11the Streaming I/O methods. In the multi-planar API, the data is held in 12planes, while the buffer structure acts as a container for the planes. 13Only pointers to buffers (planes) are exchanged, the data itself is not 14copied. These pointers, together with meta-information like timestamps 15or field parity, are stored in a struct :c:type:`v4l2_buffer`, 16argument to the :ref:`VIDIOC_QUERYBUF`, 17:ref:`VIDIOC_QBUF <VIDIOC_QBUF>` and 18:ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl. In the multi-planar API, 19some plane-specific members of struct :c:type:`v4l2_buffer`, 20such as pointers and sizes for each plane, are stored in 21struct :c:type:`v4l2_plane` instead. In that case, 22struct :c:type:`v4l2_buffer` contains an array of plane structures. 23 24Dequeued video buffers come with timestamps. The driver decides at which 25part of the frame and with which clock the timestamp is taken. Please 26see flags in the masks ``V4L2_BUF_FLAG_TIMESTAMP_MASK`` and 27``V4L2_BUF_FLAG_TSTAMP_SRC_MASK`` in :ref:`buffer-flags`. These flags 28are always valid and constant across all buffers during the whole video 29stream. Changes in these flags may take place as a side effect of 30:ref:`VIDIOC_S_INPUT <VIDIOC_G_INPUT>` or 31:ref:`VIDIOC_S_OUTPUT <VIDIOC_G_OUTPUT>` however. The 32``V4L2_BUF_FLAG_TIMESTAMP_COPY`` timestamp type which is used by e.g. on 33mem-to-mem devices is an exception to the rule: the timestamp source 34flags are copied from the OUTPUT video buffer to the CAPTURE video 35buffer. 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.. c:type:: v4l2_buffer 156 157struct v4l2_buffer 158================== 159 160.. tabularcolumns:: |p{2.9cm}|p{2.4cm}|p{12.0cm}| 161 162.. cssclass:: longtable 163 164.. flat-table:: struct v4l2_buffer 165 :header-rows: 0 166 :stub-columns: 0 167 :widths: 1 2 10 168 169 * - __u32 170 - ``index`` 171 - Number of the buffer, set by the application except when calling 172 :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>`, then it is set by the 173 driver. This field can range from zero to the number of buffers 174 allocated with the :ref:`VIDIOC_REQBUFS` ioctl 175 (struct :c:type:`v4l2_requestbuffers` 176 ``count``), plus any buffers allocated with 177 :ref:`VIDIOC_CREATE_BUFS` minus one. 178 * - __u32 179 - ``type`` 180 - Type of the buffer, same as struct 181 :c:type:`v4l2_format` ``type`` or struct 182 :c:type:`v4l2_requestbuffers` ``type``, set 183 by the application. See :c:type:`v4l2_buf_type` 184 * - __u32 185 - ``bytesused`` 186 - The number of bytes occupied by the data in the buffer. It depends 187 on the negotiated data format and may change with each buffer for 188 compressed variable size data like JPEG images. Drivers must set 189 this field when ``type`` refers to a capture stream, applications 190 when it refers to an output stream. For multiplanar formats this field 191 is ignored and the 192 ``planes`` pointer is used instead. 193 * - __u32 194 - ``flags`` 195 - Flags set by the application or driver, see :ref:`buffer-flags`. 196 * - __u32 197 - ``field`` 198 - Indicates the field order of the image in the buffer, see 199 :c:type:`v4l2_field`. This field is not used when the buffer 200 contains VBI data. Drivers must set it when ``type`` refers to a 201 capture stream, applications when it refers to an output stream. 202 * - struct timeval 203 - ``timestamp`` 204 - For capture streams this is time when the first data byte was 205 captured, as returned by the :c:func:`clock_gettime()` function 206 for the relevant clock id; see ``V4L2_BUF_FLAG_TIMESTAMP_*`` in 207 :ref:`buffer-flags`. For output streams the driver stores the 208 time at which the last data byte was actually sent out in the 209 ``timestamp`` field. This permits applications to monitor the 210 drift between the video and system clock. For output streams that 211 use ``V4L2_BUF_FLAG_TIMESTAMP_COPY`` the application has to fill 212 in the timestamp which will be copied by the driver to the capture 213 stream. 214 * - struct :c:type:`v4l2_timecode` 215 - ``timecode`` 216 - When the ``V4L2_BUF_FLAG_TIMECODE`` flag is set in ``flags``, this 217 structure contains a frame timecode. In 218 :c:type:`V4L2_FIELD_ALTERNATE <v4l2_field>` mode the top and 219 bottom field contain the same timecode. Timecodes are intended to 220 help video editing and are typically recorded on video tapes, but 221 also embedded in compressed formats like MPEG. This field is 222 independent of the ``timestamp`` and ``sequence`` fields. 223 * - __u32 224 - ``sequence`` 225 - Set by the driver, counting the frames (not fields!) in sequence. 226 This field is set for both input and output devices. 227 * - :cspan:`2` 228 229 In :c:type:`V4L2_FIELD_ALTERNATE <v4l2_field>` mode the top and 230 bottom field have the same sequence number. The count starts at 231 zero and includes dropped or repeated frames. A dropped frame was 232 received by an input device but could not be stored due to lack of 233 free buffer space. A repeated frame was displayed again by an 234 output device because the application did not pass new data in 235 time. 236 237 .. note:: 238 239 This may count the frames received e.g. over USB, without 240 taking into account the frames dropped by the remote hardware due 241 to limited compression throughput or bus bandwidth. These devices 242 identify by not enumerating any video standards, see 243 :ref:`standard`. 244 245 * - __u32 246 - ``memory`` 247 - This field must be set by applications and/or drivers in 248 accordance with the selected I/O method. See :c:type:`v4l2_memory` 249 * - union { 250 - ``m`` 251 * - __u32 252 - ``offset`` 253 - For the single-planar API and when ``memory`` is 254 ``V4L2_MEMORY_MMAP`` this is the offset of the buffer from the 255 start of the device memory. The value is returned by the driver 256 and apart of serving as parameter to the 257 :c:func:`mmap()` function not useful for applications. 258 See :ref:`mmap` for details 259 * - unsigned long 260 - ``userptr`` 261 - For the single-planar API and when ``memory`` is 262 ``V4L2_MEMORY_USERPTR`` this is a pointer to the buffer (casted to 263 unsigned long type) in virtual memory, set by the application. See 264 :ref:`userp` for details. 265 * - struct v4l2_plane 266 - ``*planes`` 267 - When using the multi-planar API, contains a userspace pointer to 268 an array of struct :c:type:`v4l2_plane`. The size of 269 the array should be put in the ``length`` field of this 270 struct :c:type:`v4l2_buffer` structure. 271 * - int 272 - ``fd`` 273 - For the single-plane API and when ``memory`` is 274 ``V4L2_MEMORY_DMABUF`` this is the file descriptor associated with 275 a DMABUF buffer. 276 * - } 277 - 278 * - __u32 279 - ``length`` 280 - Size of the buffer (not the payload) in bytes for the 281 single-planar API. This is set by the driver based on the calls to 282 :ref:`VIDIOC_REQBUFS` and/or 283 :ref:`VIDIOC_CREATE_BUFS`. For the 284 multi-planar API the application sets this to the number of 285 elements in the ``planes`` array. The driver will fill in the 286 actual number of valid elements in that array. 287 * - __u32 288 - ``reserved2`` 289 - A place holder for future extensions. Drivers and applications 290 must set this to 0. 291 * - __u32 292 - ``request_fd`` 293 - The file descriptor of the request to queue the buffer to. If the flag 294 ``V4L2_BUF_FLAG_REQUEST_FD`` is set, then the buffer will be 295 queued to this request. If the flag is not set, then this field will 296 be ignored. 297 298 The ``V4L2_BUF_FLAG_REQUEST_FD`` flag and this field are only used by 299 :ref:`ioctl VIDIOC_QBUF <VIDIOC_QBUF>` and ignored by other ioctls that 300 take a :c:type:`v4l2_buffer` as argument. 301 302 Applications should not set ``V4L2_BUF_FLAG_REQUEST_FD`` for any ioctls 303 other than :ref:`VIDIOC_QBUF <VIDIOC_QBUF>`. 304 305 If the device does not support requests, then ``EBADR`` will be returned. 306 If requests are supported but an invalid request file descriptor is 307 given, then ``EINVAL`` will be returned. 308 309 310.. c:type:: v4l2_plane 311 312struct v4l2_plane 313================= 314 315.. tabularcolumns:: |p{3.5cm}|p{3.5cm}|p{10.3cm}| 316 317.. cssclass:: longtable 318 319.. flat-table:: 320 :header-rows: 0 321 :stub-columns: 0 322 :widths: 1 1 2 323 324 * - __u32 325 - ``bytesused`` 326 - The number of bytes occupied by data in the plane (its payload). 327 Drivers must set this field when ``type`` refers to a capture 328 stream, applications when it refers to an output stream. 329 330 .. note:: 331 332 Note that the actual image data starts at ``data_offset`` 333 which may not be 0. 334 * - __u32 335 - ``length`` 336 - Size in bytes of the plane (not its payload). This is set by the 337 driver based on the calls to 338 :ref:`VIDIOC_REQBUFS` and/or 339 :ref:`VIDIOC_CREATE_BUFS`. 340 * - union { 341 - ``m`` 342 * - __u32 343 - ``mem_offset`` 344 - When the memory type in the containing struct 345 :c:type:`v4l2_buffer` is ``V4L2_MEMORY_MMAP``, this 346 is the value that should be passed to :c:func:`mmap()`, 347 similar to the ``offset`` field in struct 348 :c:type:`v4l2_buffer`. 349 * - unsigned long 350 - ``userptr`` 351 - When the memory type in the containing struct 352 :c:type:`v4l2_buffer` is ``V4L2_MEMORY_USERPTR``, 353 this is a userspace pointer to the memory allocated for this plane 354 by an application. 355 * - int 356 - ``fd`` 357 - When the memory type in the containing struct 358 :c:type:`v4l2_buffer` is ``V4L2_MEMORY_DMABUF``, 359 this is a file descriptor associated with a DMABUF buffer, similar 360 to the ``fd`` field in struct :c:type:`v4l2_buffer`. 361 * - } 362 - 363 * - __u32 364 - ``data_offset`` 365 - Offset in bytes to video data in the plane. Drivers must set this 366 field when ``type`` refers to a capture stream, applications when 367 it refers to an output stream. 368 369 .. note:: 370 371 That data_offset is included in ``bytesused``. So the 372 size of the image in the plane is ``bytesused``-``data_offset`` 373 at offset ``data_offset`` from the start of the plane. 374 * - __u32 375 - ``reserved[11]`` 376 - Reserved for future use. Should be zeroed by drivers and 377 applications. 378 379 380.. c:type:: v4l2_buf_type 381 382enum v4l2_buf_type 383================== 384 385.. cssclass:: longtable 386 387.. tabularcolumns:: |p{7.8cm}|p{0.6cm}|p{8.9cm}| 388 389.. flat-table:: 390 :header-rows: 0 391 :stub-columns: 0 392 :widths: 4 1 9 393 394 * - ``V4L2_BUF_TYPE_VIDEO_CAPTURE`` 395 - 1 396 - Buffer of a single-planar video capture stream, see 397 :ref:`capture`. 398 * - ``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE`` 399 - 9 400 - Buffer of a multi-planar video capture stream, see 401 :ref:`capture`. 402 * - ``V4L2_BUF_TYPE_VIDEO_OUTPUT`` 403 - 2 404 - Buffer of a single-planar video output stream, see 405 :ref:`output`. 406 * - ``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE`` 407 - 10 408 - Buffer of a multi-planar video output stream, see :ref:`output`. 409 * - ``V4L2_BUF_TYPE_VIDEO_OVERLAY`` 410 - 3 411 - Buffer for video overlay, see :ref:`overlay`. 412 * - ``V4L2_BUF_TYPE_VBI_CAPTURE`` 413 - 4 414 - Buffer of a raw VBI capture stream, see :ref:`raw-vbi`. 415 * - ``V4L2_BUF_TYPE_VBI_OUTPUT`` 416 - 5 417 - Buffer of a raw VBI output stream, see :ref:`raw-vbi`. 418 * - ``V4L2_BUF_TYPE_SLICED_VBI_CAPTURE`` 419 - 6 420 - Buffer of a sliced VBI capture stream, see :ref:`sliced`. 421 * - ``V4L2_BUF_TYPE_SLICED_VBI_OUTPUT`` 422 - 7 423 - Buffer of a sliced VBI output stream, see :ref:`sliced`. 424 * - ``V4L2_BUF_TYPE_VIDEO_OUTPUT_OVERLAY`` 425 - 8 426 - Buffer for video output overlay (OSD), see :ref:`osd`. 427 * - ``V4L2_BUF_TYPE_SDR_CAPTURE`` 428 - 11 429 - Buffer for Software Defined Radio (SDR) capture stream, see 430 :ref:`sdr`. 431 * - ``V4L2_BUF_TYPE_SDR_OUTPUT`` 432 - 12 433 - Buffer for Software Defined Radio (SDR) output stream, see 434 :ref:`sdr`. 435 * - ``V4L2_BUF_TYPE_META_CAPTURE`` 436 - 13 437 - Buffer for metadata capture, see :ref:`metadata`. 438 * - ``V4L2_BUF_TYPE_META_OUTPUT`` 439 - 14 440 - Buffer for metadata output, see :ref:`metadata`. 441 442 443.. _buffer-flags: 444 445Buffer Flags 446============ 447 448.. raw:: latex 449 450 \footnotesize 451 452.. tabularcolumns:: |p{6.5cm}|p{1.8cm}|p{9.0cm}| 453 454.. cssclass:: longtable 455 456.. flat-table:: 457 :header-rows: 0 458 :stub-columns: 0 459 :widths: 65 18 70 460 461 * .. _`V4L2-BUF-FLAG-MAPPED`: 462 463 - ``V4L2_BUF_FLAG_MAPPED`` 464 - 0x00000001 465 - The buffer resides in device memory and has been mapped into the 466 application's address space, see :ref:`mmap` for details. 467 Drivers set or clear this flag when the 468 :ref:`VIDIOC_QUERYBUF`, 469 :ref:`VIDIOC_QBUF` or 470 :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl is called. Set by the 471 driver. 472 * .. _`V4L2-BUF-FLAG-QUEUED`: 473 474 - ``V4L2_BUF_FLAG_QUEUED`` 475 - 0x00000002 476 - Internally drivers maintain two buffer queues, an incoming and 477 outgoing queue. When this flag is set, the buffer is currently on 478 the incoming queue. It automatically moves to the outgoing queue 479 after the buffer has been filled (capture devices) or displayed 480 (output devices). Drivers set or clear this flag when the 481 ``VIDIOC_QUERYBUF`` ioctl is called. After (successful) calling 482 the ``VIDIOC_QBUF``\ ioctl it is always set and after 483 ``VIDIOC_DQBUF`` always cleared. 484 * .. _`V4L2-BUF-FLAG-DONE`: 485 486 - ``V4L2_BUF_FLAG_DONE`` 487 - 0x00000004 488 - When this flag is set, the buffer is currently on the outgoing 489 queue, ready to be dequeued from the driver. Drivers set or clear 490 this flag when the ``VIDIOC_QUERYBUF`` ioctl is called. After 491 calling the ``VIDIOC_QBUF`` or ``VIDIOC_DQBUF`` it is always 492 cleared. Of course a buffer cannot be on both queues at the same 493 time, the ``V4L2_BUF_FLAG_QUEUED`` and ``V4L2_BUF_FLAG_DONE`` flag 494 are mutually exclusive. They can be both cleared however, then the 495 buffer is in "dequeued" state, in the application domain so to 496 say. 497 * .. _`V4L2-BUF-FLAG-ERROR`: 498 499 - ``V4L2_BUF_FLAG_ERROR`` 500 - 0x00000040 501 - When this flag is set, the buffer has been dequeued successfully, 502 although the data might have been corrupted. This is recoverable, 503 streaming may continue as normal and the buffer may be reused 504 normally. Drivers set this flag when the ``VIDIOC_DQBUF`` ioctl is 505 called. 506 * .. _`V4L2-BUF-FLAG-IN-REQUEST`: 507 508 - ``V4L2_BUF_FLAG_IN_REQUEST`` 509 - 0x00000080 510 - This buffer is part of a request that hasn't been queued yet. 511 * .. _`V4L2-BUF-FLAG-KEYFRAME`: 512 513 - ``V4L2_BUF_FLAG_KEYFRAME`` 514 - 0x00000008 515 - Drivers set or clear this flag when calling the ``VIDIOC_DQBUF`` 516 ioctl. It may be set by video capture devices when the buffer 517 contains a compressed image which is a key frame (or field), i. e. 518 can be decompressed on its own. Also known as an I-frame. 519 Applications can set this bit when ``type`` refers to an output 520 stream. 521 * .. _`V4L2-BUF-FLAG-PFRAME`: 522 523 - ``V4L2_BUF_FLAG_PFRAME`` 524 - 0x00000010 525 - Similar to ``V4L2_BUF_FLAG_KEYFRAME`` this flags predicted frames 526 or fields which contain only differences to a previous key frame. 527 Applications can set this bit when ``type`` refers to an output 528 stream. 529 * .. _`V4L2-BUF-FLAG-BFRAME`: 530 531 - ``V4L2_BUF_FLAG_BFRAME`` 532 - 0x00000020 533 - Similar to ``V4L2_BUF_FLAG_KEYFRAME`` this flags a bi-directional 534 predicted frame or field which contains only the differences 535 between the current frame and both the preceding and following key 536 frames to specify its content. Applications can set this bit when 537 ``type`` refers to an output stream. 538 * .. _`V4L2-BUF-FLAG-TIMECODE`: 539 540 - ``V4L2_BUF_FLAG_TIMECODE`` 541 - 0x00000100 542 - The ``timecode`` field is valid. Drivers set or clear this flag 543 when the ``VIDIOC_DQBUF`` ioctl is called. Applications can set 544 this bit and the corresponding ``timecode`` structure when 545 ``type`` refers to an output stream. 546 * .. _`V4L2-BUF-FLAG-PREPARED`: 547 548 - ``V4L2_BUF_FLAG_PREPARED`` 549 - 0x00000400 550 - The buffer has been prepared for I/O and can be queued by the 551 application. Drivers set or clear this flag when the 552 :ref:`VIDIOC_QUERYBUF <VIDIOC_QUERYBUF>`, 553 :ref:`VIDIOC_PREPARE_BUF <VIDIOC_QBUF>`, 554 :ref:`VIDIOC_QBUF <VIDIOC_QBUF>` or 555 :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl is called. 556 * .. _`V4L2-BUF-FLAG-NO-CACHE-INVALIDATE`: 557 558 - ``V4L2_BUF_FLAG_NO_CACHE_INVALIDATE`` 559 - 0x00000800 560 - Caches do not have to be invalidated for this buffer. Typically 561 applications shall use this flag if the data captured in the 562 buffer is not going to be touched by the CPU, instead the buffer 563 will, probably, be passed on to a DMA-capable hardware unit for 564 further processing or output. This flag is ignored unless the 565 queue is used for :ref:`memory mapping <mmap>` streaming I/O and 566 reports :ref:`V4L2_BUF_CAP_SUPPORTS_MMAP_CACHE_HINTS 567 <V4L2-BUF-CAP-SUPPORTS-MMAP-CACHE-HINTS>` capability. 568 * .. _`V4L2-BUF-FLAG-NO-CACHE-CLEAN`: 569 570 - ``V4L2_BUF_FLAG_NO_CACHE_CLEAN`` 571 - 0x00001000 572 - Caches do not have to be cleaned for this buffer. Typically 573 applications shall use this flag for output buffers if the data in 574 this buffer has not been created by the CPU but by some 575 DMA-capable unit, in which case caches have not been used. This flag 576 is ignored unless the queue is used for :ref:`memory mapping <mmap>` 577 streaming I/O and reports :ref:`V4L2_BUF_CAP_SUPPORTS_MMAP_CACHE_HINTS 578 <V4L2-BUF-CAP-SUPPORTS-MMAP-CACHE-HINTS>` capability. 579 * .. _`V4L2-BUF-FLAG-M2M-HOLD-CAPTURE-BUF`: 580 581 - ``V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF`` 582 - 0x00000200 583 - Only valid if struct :c:type:`v4l2_requestbuffers` flag ``V4L2_BUF_CAP_SUPPORTS_M2M_HOLD_CAPTURE_BUF`` is 584 set. It is typically used with stateless decoders where multiple 585 output buffers each decode to a slice of the decoded frame. 586 Applications can set this flag when queueing the output buffer 587 to prevent the driver from dequeueing the capture buffer after 588 the output buffer has been decoded (i.e. the capture buffer is 589 'held'). If the timestamp of this output buffer differs from that 590 of the previous output buffer, then that indicates the start of a 591 new frame and the previously held capture buffer is dequeued. 592 * .. _`V4L2-BUF-FLAG-LAST`: 593 594 - ``V4L2_BUF_FLAG_LAST`` 595 - 0x00100000 596 - Last buffer produced by the hardware. mem2mem codec drivers set 597 this flag on the capture queue for the last buffer when the 598 :ref:`VIDIOC_QUERYBUF` or 599 :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl is called. Due to 600 hardware limitations, the last buffer may be empty. In this case 601 the driver will set the ``bytesused`` field to 0, regardless of 602 the format. Any subsequent call to the 603 :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl will not block anymore, 604 but return an ``EPIPE`` error code. 605 * .. _`V4L2-BUF-FLAG-REQUEST-FD`: 606 607 - ``V4L2_BUF_FLAG_REQUEST_FD`` 608 - 0x00800000 609 - The ``request_fd`` field contains a valid file descriptor. 610 * .. _`V4L2-BUF-FLAG-TIMESTAMP-MASK`: 611 612 - ``V4L2_BUF_FLAG_TIMESTAMP_MASK`` 613 - 0x0000e000 614 - Mask for timestamp types below. To test the timestamp type, mask 615 out bits not belonging to timestamp type by performing a logical 616 and operation with buffer flags and timestamp mask. 617 * .. _`V4L2-BUF-FLAG-TIMESTAMP-UNKNOWN`: 618 619 - ``V4L2_BUF_FLAG_TIMESTAMP_UNKNOWN`` 620 - 0x00000000 621 - Unknown timestamp type. This type is used by drivers before Linux 622 3.9 and may be either monotonic (see below) or realtime (wall 623 clock). Monotonic clock has been favoured in embedded systems 624 whereas most of the drivers use the realtime clock. Either kinds 625 of timestamps are available in user space via 626 :c:func:`clock_gettime` using clock IDs ``CLOCK_MONOTONIC`` 627 and ``CLOCK_REALTIME``, respectively. 628 * .. _`V4L2-BUF-FLAG-TIMESTAMP-MONOTONIC`: 629 630 - ``V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC`` 631 - 0x00002000 632 - The buffer timestamp has been taken from the ``CLOCK_MONOTONIC`` 633 clock. To access the same clock outside V4L2, use 634 :c:func:`clock_gettime`. 635 * .. _`V4L2-BUF-FLAG-TIMESTAMP-COPY`: 636 637 - ``V4L2_BUF_FLAG_TIMESTAMP_COPY`` 638 - 0x00004000 639 - The CAPTURE buffer timestamp has been taken from the corresponding 640 OUTPUT buffer. This flag applies only to mem2mem devices. 641 * .. _`V4L2-BUF-FLAG-TSTAMP-SRC-MASK`: 642 643 - ``V4L2_BUF_FLAG_TSTAMP_SRC_MASK`` 644 - 0x00070000 645 - Mask for timestamp sources below. The timestamp source defines the 646 point of time the timestamp is taken in relation to the frame. 647 Logical 'and' operation between the ``flags`` field and 648 ``V4L2_BUF_FLAG_TSTAMP_SRC_MASK`` produces the value of the 649 timestamp source. Applications must set the timestamp source when 650 ``type`` refers to an output stream and 651 ``V4L2_BUF_FLAG_TIMESTAMP_COPY`` is set. 652 * .. _`V4L2-BUF-FLAG-TSTAMP-SRC-EOF`: 653 654 - ``V4L2_BUF_FLAG_TSTAMP_SRC_EOF`` 655 - 0x00000000 656 - End Of Frame. The buffer timestamp has been taken when the last 657 pixel of the frame has been received or the last pixel of the 658 frame has been transmitted. In practice, software generated 659 timestamps will typically be read from the clock a small amount of 660 time after the last pixel has been received or transmitten, 661 depending on the system and other activity in it. 662 * .. _`V4L2-BUF-FLAG-TSTAMP-SRC-SOE`: 663 664 - ``V4L2_BUF_FLAG_TSTAMP_SRC_SOE`` 665 - 0x00010000 666 - Start Of Exposure. The buffer timestamp has been taken when the 667 exposure of the frame has begun. This is only valid for the 668 ``V4L2_BUF_TYPE_VIDEO_CAPTURE`` buffer type. 669 670.. raw:: latex 671 672 \normalsize 673 674enum v4l2_memory 675================ 676 677.. tabularcolumns:: |p{5.0cm}|p{0.8cm}|p{11.5cm}| 678 679.. flat-table:: 680 :header-rows: 0 681 :stub-columns: 0 682 :widths: 3 1 4 683 684 * - ``V4L2_MEMORY_MMAP`` 685 - 1 686 - The buffer is used for :ref:`memory mapping <mmap>` I/O. 687 * - ``V4L2_MEMORY_USERPTR`` 688 - 2 689 - The buffer is used for :ref:`user pointer <userp>` I/O. 690 * - ``V4L2_MEMORY_OVERLAY`` 691 - 3 692 - [to do] 693 * - ``V4L2_MEMORY_DMABUF`` 694 - 4 695 - The buffer is used for :ref:`DMA shared buffer <dmabuf>` I/O. 696 697.. _memory-flags: 698 699Memory Consistency Flags 700------------------------ 701 702.. raw:: latex 703 704 \small 705 706.. tabularcolumns:: |p{7.0cm}|p{2.1cm}|p{8.4cm}| 707 708.. cssclass:: longtable 709 710.. flat-table:: 711 :header-rows: 0 712 :stub-columns: 0 713 :widths: 3 1 4 714 715 * .. _`V4L2-MEMORY-FLAG-NON-COHERENT`: 716 717 - ``V4L2_MEMORY_FLAG_NON_COHERENT`` 718 - 0x00000001 719 - A buffer is allocated either in coherent (it will be automatically 720 coherent between the CPU and the bus) or non-coherent memory. The 721 latter can provide performance gains, for instance the CPU cache 722 sync/flush operations can be avoided if the buffer is accessed by the 723 corresponding device only and the CPU does not read/write to/from that 724 buffer. However, this requires extra care from the driver -- it must 725 guarantee memory consistency by issuing a cache flush/sync when 726 consistency is needed. If this flag is set V4L2 will attempt to 727 allocate the buffer in non-coherent memory. The flag takes effect 728 only if the buffer is used for :ref:`memory mapping <mmap>` I/O and the 729 queue reports the :ref:`V4L2_BUF_CAP_SUPPORTS_MMAP_CACHE_HINTS 730 <V4L2-BUF-CAP-SUPPORTS-MMAP-CACHE-HINTS>` capability. 731 732.. raw:: latex 733 734 \normalsize 735 736Timecodes 737========= 738 739The :c:type:`v4l2_buffer_timecode` structure is designed to hold a 740:ref:`smpte12m` or similar timecode. 741(struct :c:type:`timeval` timestamps are stored in the struct 742:c:type:`v4l2_buffer` ``timestamp`` field.) 743 744.. c:type:: v4l2_timecode 745 746struct v4l2_timecode 747-------------------- 748 749.. tabularcolumns:: |p{1.4cm}|p{2.8cm}|p{13.1cm}| 750 751.. flat-table:: 752 :header-rows: 0 753 :stub-columns: 0 754 :widths: 1 1 2 755 756 * - __u32 757 - ``type`` 758 - Frame rate the timecodes are based on, see :ref:`timecode-type`. 759 * - __u32 760 - ``flags`` 761 - Timecode flags, see :ref:`timecode-flags`. 762 * - __u8 763 - ``frames`` 764 - Frame count, 0 ... 23/24/29/49/59, depending on the type of 765 timecode. 766 * - __u8 767 - ``seconds`` 768 - Seconds count, 0 ... 59. This is a binary, not BCD number. 769 * - __u8 770 - ``minutes`` 771 - Minutes count, 0 ... 59. This is a binary, not BCD number. 772 * - __u8 773 - ``hours`` 774 - Hours count, 0 ... 29. This is a binary, not BCD number. 775 * - __u8 776 - ``userbits``\ [4] 777 - The "user group" bits from the timecode. 778 779 780.. _timecode-type: 781 782Timecode Types 783-------------- 784 785.. flat-table:: 786 :header-rows: 0 787 :stub-columns: 0 788 :widths: 3 1 4 789 790 * - ``V4L2_TC_TYPE_24FPS`` 791 - 1 792 - 24 frames per second, i. e. film. 793 * - ``V4L2_TC_TYPE_25FPS`` 794 - 2 795 - 25 frames per second, i. e. PAL or SECAM video. 796 * - ``V4L2_TC_TYPE_30FPS`` 797 - 3 798 - 30 frames per second, i. e. NTSC video. 799 * - ``V4L2_TC_TYPE_50FPS`` 800 - 4 801 - 802 * - ``V4L2_TC_TYPE_60FPS`` 803 - 5 804 - 805 806 807.. _timecode-flags: 808 809Timecode Flags 810-------------- 811 812.. tabularcolumns:: |p{6.6cm}|p{1.4cm}|p{9.3cm}| 813 814.. flat-table:: 815 :header-rows: 0 816 :stub-columns: 0 817 :widths: 3 1 4 818 819 * - ``V4L2_TC_FLAG_DROPFRAME`` 820 - 0x0001 821 - Indicates "drop frame" semantics for counting frames in 29.97 fps 822 material. When set, frame numbers 0 and 1 at the start of each 823 minute, except minutes 0, 10, 20, 30, 40, 50 are omitted from the 824 count. 825 * - ``V4L2_TC_FLAG_COLORFRAME`` 826 - 0x0002 827 - The "color frame" flag. 828 * - ``V4L2_TC_USERBITS_field`` 829 - 0x000C 830 - Field mask for the "binary group flags". 831 * - ``V4L2_TC_USERBITS_USERDEFINED`` 832 - 0x0000 833 - Unspecified format. 834 * - ``V4L2_TC_USERBITS_8BITCHARS`` 835 - 0x0008 836 - 8-bit ISO characters. 837