1.. -*- coding: utf-8; mode: rst -*- 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` 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 struct 20struct :c:type:`v4l2_plane` instead. In that case, struct 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{1.3cm}|p{10.5cm}| 162 163.. cssclass:: longtable 164 165.. flat-table:: struct v4l2_buffer 166 :header-rows: 0 167 :stub-columns: 0 168 :widths: 1 2 1 10 169 170 * - __u32 171 - ``index`` 172 - 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. 180 * - __u32 181 - ``type`` 182 - 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` 187 * - __u32 188 - ``bytesused`` 189 - 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. 199 * - __u32 200 - ``flags`` 201 - 202 - Flags set by the application or driver, see :ref:`buffer-flags`. 203 * - __u32 204 - ``field`` 205 - 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. 210 * - struct timeval 211 - ``timestamp`` 212 - 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 222 stream. 223 * - struct :c:type:`v4l2_timecode` 224 - ``timecode`` 225 - 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. 234 * - __u32 235 - ``sequence`` 236 - 237 - Set by the driver, counting the frames (not fields!) in sequence. 238 This field is set for both input and output devices. 239 * - :cspan:`3` 240 241 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 247 time. 248 249 .. note:: 250 251 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 255 :ref:`standard`. 256 257 * - __u32 258 - ``memory`` 259 - 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` 262 * - union 263 - ``m`` 264 * - 265 - __u32 266 - ``offset`` 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 273 * - 274 - unsigned long 275 - ``userptr`` 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. 280 * - 281 - struct v4l2_plane 282 - ``*planes`` 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. 287 * - 288 - int 289 - ``fd`` 290 - For the single-plane API and when ``memory`` is 291 ``V4L2_MEMORY_DMABUF`` this is the file descriptor associated with 292 a DMABUF buffer. 293 * - __u32 294 - ``length`` 295 - 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. 303 * - __u32 304 - ``reserved2`` 305 - 306 - A place holder for future extensions. Drivers and applications 307 must set this to 0. 308 * - __u32 309 - ``reserved`` 310 - 311 - A place holder for future extensions. Drivers and applications 312 must set this to 0. 313 314 315 316.. c:type:: v4l2_plane 317 318struct v4l2_plane 319================= 320 321.. tabularcolumns:: |p{3.5cm}|p{3.5cm}|p{3.5cm}|p{7.0cm}| 322 323.. cssclass:: longtable 324 325.. flat-table:: 326 :header-rows: 0 327 :stub-columns: 0 328 :widths: 1 1 1 2 329 330 * - __u32 331 - ``bytesused`` 332 - 333 - The number of bytes occupied by data in the plane (its payload). 334 Drivers must set this field when ``type`` refers to a capture 335 stream, applications when it refers to an output stream. If the 336 application sets this to 0 for an output stream, then 337 ``bytesused`` will be set to the size of the plane (see the 338 ``length`` field of this struct) by the driver. 339 340 .. note:: 341 342 Note that the actual image data starts at ``data_offset`` 343 which may not be 0. 344 * - __u32 345 - ``length`` 346 - 347 - Size in bytes of the plane (not its payload). This is set by the 348 driver based on the calls to 349 :ref:`VIDIOC_REQBUFS` and/or 350 :ref:`VIDIOC_CREATE_BUFS`. 351 * - union 352 - ``m`` 353 - 354 - 355 * - 356 - __u32 357 - ``mem_offset`` 358 - When the memory type in the containing struct 359 :c:type:`v4l2_buffer` is ``V4L2_MEMORY_MMAP``, this 360 is the value that should be passed to :ref:`mmap() <func-mmap>`, 361 similar to the ``offset`` field in struct 362 :c:type:`v4l2_buffer`. 363 * - 364 - unsigned long 365 - ``userptr`` 366 - When the memory type in the containing struct 367 :c:type:`v4l2_buffer` is ``V4L2_MEMORY_USERPTR``, 368 this is a userspace pointer to the memory allocated for this plane 369 by an application. 370 * - 371 - int 372 - ``fd`` 373 - When the memory type in the containing struct 374 :c:type:`v4l2_buffer` is ``V4L2_MEMORY_DMABUF``, 375 this is a file descriptor associated with a DMABUF buffer, similar 376 to the ``fd`` field in struct :c:type:`v4l2_buffer`. 377 * - __u32 378 - ``data_offset`` 379 - 380 - Offset in bytes to video data in the plane. Drivers must set this 381 field when ``type`` refers to a capture stream, applications when 382 it refers to an output stream. 383 384 .. note:: 385 386 That data_offset is included in ``bytesused``. So the 387 size of the image in the plane is ``bytesused``-``data_offset`` 388 at offset ``data_offset`` from the start of the plane. 389 * - __u32 390 - ``reserved[11]`` 391 - 392 - Reserved for future use. Should be zeroed by drivers and 393 applications. 394 395 396 397.. c:type:: v4l2_buf_type 398 399enum v4l2_buf_type 400================== 401 402.. cssclass:: longtable 403 404.. tabularcolumns:: |p{7.2cm}|p{0.6cm}|p{9.7cm}| 405 406.. flat-table:: 407 :header-rows: 0 408 :stub-columns: 0 409 :widths: 4 1 9 410 411 * - ``V4L2_BUF_TYPE_VIDEO_CAPTURE`` 412 - 1 413 - Buffer of a single-planar video capture stream, see 414 :ref:`capture`. 415 * - ``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE`` 416 - 9 417 - Buffer of a multi-planar video capture stream, see 418 :ref:`capture`. 419 * - ``V4L2_BUF_TYPE_VIDEO_OUTPUT`` 420 - 2 421 - Buffer of a single-planar video output stream, see 422 :ref:`output`. 423 * - ``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE`` 424 - 10 425 - Buffer of a multi-planar video output stream, see :ref:`output`. 426 * - ``V4L2_BUF_TYPE_VIDEO_OVERLAY`` 427 - 3 428 - Buffer for video overlay, see :ref:`overlay`. 429 * - ``V4L2_BUF_TYPE_VBI_CAPTURE`` 430 - 4 431 - Buffer of a raw VBI capture stream, see :ref:`raw-vbi`. 432 * - ``V4L2_BUF_TYPE_VBI_OUTPUT`` 433 - 5 434 - Buffer of a raw VBI output stream, see :ref:`raw-vbi`. 435 * - ``V4L2_BUF_TYPE_SLICED_VBI_CAPTURE`` 436 - 6 437 - Buffer of a sliced VBI capture stream, see :ref:`sliced`. 438 * - ``V4L2_BUF_TYPE_SLICED_VBI_OUTPUT`` 439 - 7 440 - Buffer of a sliced VBI output stream, see :ref:`sliced`. 441 * - ``V4L2_BUF_TYPE_VIDEO_OUTPUT_OVERLAY`` 442 - 8 443 - Buffer for video output overlay (OSD), see :ref:`osd`. 444 * - ``V4L2_BUF_TYPE_SDR_CAPTURE`` 445 - 11 446 - Buffer for Software Defined Radio (SDR) capture stream, see 447 :ref:`sdr`. 448 * - ``V4L2_BUF_TYPE_SDR_OUTPUT`` 449 - 12 450 - Buffer for Software Defined Radio (SDR) output stream, see 451 :ref:`sdr`. 452 * - ``V4L2_BUF_TYPE_META_CAPTURE`` 453 - 13 454 - Buffer for metadata capture, see :ref:`metadata`. 455 456 457 458.. _buffer-flags: 459 460Buffer Flags 461============ 462 463.. tabularcolumns:: |p{7.0cm}|p{2.2cm}|p{8.3cm}| 464 465.. cssclass:: longtable 466 467.. flat-table:: 468 :header-rows: 0 469 :stub-columns: 0 470 :widths: 3 1 4 471 472 * .. _`V4L2-BUF-FLAG-MAPPED`: 473 474 - ``V4L2_BUF_FLAG_MAPPED`` 475 - 0x00000001 476 - The buffer resides in device memory and has been mapped into the 477 application's address space, see :ref:`mmap` for details. 478 Drivers set or clear this flag when the 479 :ref:`VIDIOC_QUERYBUF`, 480 :ref:`VIDIOC_QBUF` or 481 :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl is called. Set by the 482 driver. 483 * .. _`V4L2-BUF-FLAG-QUEUED`: 484 485 - ``V4L2_BUF_FLAG_QUEUED`` 486 - 0x00000002 487 - Internally drivers maintain two buffer queues, an incoming and 488 outgoing queue. When this flag is set, the buffer is currently on 489 the incoming queue. It automatically moves to the outgoing queue 490 after the buffer has been filled (capture devices) or displayed 491 (output devices). Drivers set or clear this flag when the 492 ``VIDIOC_QUERYBUF`` ioctl is called. After (successful) calling 493 the ``VIDIOC_QBUF``\ ioctl it is always set and after 494 ``VIDIOC_DQBUF`` always cleared. 495 * .. _`V4L2-BUF-FLAG-DONE`: 496 497 - ``V4L2_BUF_FLAG_DONE`` 498 - 0x00000004 499 - When this flag is set, the buffer is currently on the outgoing 500 queue, ready to be dequeued from the driver. Drivers set or clear 501 this flag when the ``VIDIOC_QUERYBUF`` ioctl is called. After 502 calling the ``VIDIOC_QBUF`` or ``VIDIOC_DQBUF`` it is always 503 cleared. Of course a buffer cannot be on both queues at the same 504 time, the ``V4L2_BUF_FLAG_QUEUED`` and ``V4L2_BUF_FLAG_DONE`` flag 505 are mutually exclusive. They can be both cleared however, then the 506 buffer is in "dequeued" state, in the application domain so to 507 say. 508 * .. _`V4L2-BUF-FLAG-ERROR`: 509 510 - ``V4L2_BUF_FLAG_ERROR`` 511 - 0x00000040 512 - When this flag is set, the buffer has been dequeued successfully, 513 although the data might have been corrupted. This is recoverable, 514 streaming may continue as normal and the buffer may be reused 515 normally. Drivers set this flag when the ``VIDIOC_DQBUF`` ioctl is 516 called. 517 * .. _`V4L2-BUF-FLAG-KEYFRAME`: 518 519 - ``V4L2_BUF_FLAG_KEYFRAME`` 520 - 0x00000008 521 - Drivers set or clear this flag when calling the ``VIDIOC_DQBUF`` 522 ioctl. It may be set by video capture devices when the buffer 523 contains a compressed image which is a key frame (or field), i. e. 524 can be decompressed on its own. Also known as an I-frame. 525 Applications can set this bit when ``type`` refers to an output 526 stream. 527 * .. _`V4L2-BUF-FLAG-PFRAME`: 528 529 - ``V4L2_BUF_FLAG_PFRAME`` 530 - 0x00000010 531 - Similar to ``V4L2_BUF_FLAG_KEYFRAME`` this flags predicted frames 532 or fields which contain only differences to a previous key frame. 533 Applications can set this bit when ``type`` refers to an output 534 stream. 535 * .. _`V4L2-BUF-FLAG-BFRAME`: 536 537 - ``V4L2_BUF_FLAG_BFRAME`` 538 - 0x00000020 539 - Similar to ``V4L2_BUF_FLAG_KEYFRAME`` this flags a bi-directional 540 predicted frame or field which contains only the differences 541 between the current frame and both the preceding and following key 542 frames to specify its content. Applications can set this bit when 543 ``type`` refers to an output stream. 544 * .. _`V4L2-BUF-FLAG-TIMECODE`: 545 546 - ``V4L2_BUF_FLAG_TIMECODE`` 547 - 0x00000100 548 - The ``timecode`` field is valid. Drivers set or clear this flag 549 when the ``VIDIOC_DQBUF`` ioctl is called. Applications can set 550 this bit and the corresponding ``timecode`` structure when 551 ``type`` refers to an output stream. 552 * .. _`V4L2-BUF-FLAG-PREPARED`: 553 554 - ``V4L2_BUF_FLAG_PREPARED`` 555 - 0x00000400 556 - The buffer has been prepared for I/O and can be queued by the 557 application. Drivers set or clear this flag when the 558 :ref:`VIDIOC_QUERYBUF`, 559 :ref:`VIDIOC_PREPARE_BUF <VIDIOC_QBUF>`, 560 :ref:`VIDIOC_QBUF` or 561 :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl is called. 562 * .. _`V4L2-BUF-FLAG-NO-CACHE-INVALIDATE`: 563 564 - ``V4L2_BUF_FLAG_NO_CACHE_INVALIDATE`` 565 - 0x00000800 566 - Caches do not have to be invalidated for this buffer. Typically 567 applications shall use this flag if the data captured in the 568 buffer is not going to be touched by the CPU, instead the buffer 569 will, probably, be passed on to a DMA-capable hardware unit for 570 further processing or output. 571 * .. _`V4L2-BUF-FLAG-NO-CACHE-CLEAN`: 572 573 - ``V4L2_BUF_FLAG_NO_CACHE_CLEAN`` 574 - 0x00001000 575 - Caches do not have to be cleaned for this buffer. Typically 576 applications shall use this flag for output buffers if the data in 577 this buffer has not been created by the CPU but by some 578 DMA-capable unit, in which case caches have not been used. 579 * .. _`V4L2-BUF-FLAG-LAST`: 580 581 - ``V4L2_BUF_FLAG_LAST`` 582 - 0x00100000 583 - Last buffer produced by the hardware. mem2mem codec drivers set 584 this flag on the capture queue for the last buffer when the 585 :ref:`VIDIOC_QUERYBUF` or 586 :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl is called. Due to 587 hardware limitations, the last buffer may be empty. In this case 588 the driver will set the ``bytesused`` field to 0, regardless of 589 the format. Any Any subsequent call to the 590 :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl will not block anymore, 591 but return an ``EPIPE`` error code. 592 * .. _`V4L2-BUF-FLAG-TIMESTAMP-MASK`: 593 594 - ``V4L2_BUF_FLAG_TIMESTAMP_MASK`` 595 - 0x0000e000 596 - Mask for timestamp types below. To test the timestamp type, mask 597 out bits not belonging to timestamp type by performing a logical 598 and operation with buffer flags and timestamp mask. 599 * .. _`V4L2-BUF-FLAG-TIMESTAMP-UNKNOWN`: 600 601 - ``V4L2_BUF_FLAG_TIMESTAMP_UNKNOWN`` 602 - 0x00000000 603 - Unknown timestamp type. This type is used by drivers before Linux 604 3.9 and may be either monotonic (see below) or realtime (wall 605 clock). Monotonic clock has been favoured in embedded systems 606 whereas most of the drivers use the realtime clock. Either kinds 607 of timestamps are available in user space via 608 :c:func:`clock_gettime` using clock IDs ``CLOCK_MONOTONIC`` 609 and ``CLOCK_REALTIME``, respectively. 610 * .. _`V4L2-BUF-FLAG-TIMESTAMP-MONOTONIC`: 611 612 - ``V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC`` 613 - 0x00002000 614 - The buffer timestamp has been taken from the ``CLOCK_MONOTONIC`` 615 clock. To access the same clock outside V4L2, use 616 :c:func:`clock_gettime`. 617 * .. _`V4L2-BUF-FLAG-TIMESTAMP-COPY`: 618 619 - ``V4L2_BUF_FLAG_TIMESTAMP_COPY`` 620 - 0x00004000 621 - The CAPTURE buffer timestamp has been taken from the corresponding 622 OUTPUT buffer. This flag applies only to mem2mem devices. 623 * .. _`V4L2-BUF-FLAG-TSTAMP-SRC-MASK`: 624 625 - ``V4L2_BUF_FLAG_TSTAMP_SRC_MASK`` 626 - 0x00070000 627 - Mask for timestamp sources below. The timestamp source defines the 628 point of time the timestamp is taken in relation to the frame. 629 Logical 'and' operation between the ``flags`` field and 630 ``V4L2_BUF_FLAG_TSTAMP_SRC_MASK`` produces the value of the 631 timestamp source. Applications must set the timestamp source when 632 ``type`` refers to an output stream and 633 ``V4L2_BUF_FLAG_TIMESTAMP_COPY`` is set. 634 * .. _`V4L2-BUF-FLAG-TSTAMP-SRC-EOF`: 635 636 - ``V4L2_BUF_FLAG_TSTAMP_SRC_EOF`` 637 - 0x00000000 638 - End Of Frame. The buffer timestamp has been taken when the last 639 pixel of the frame has been received or the last pixel of the 640 frame has been transmitted. In practice, software generated 641 timestamps will typically be read from the clock a small amount of 642 time after the last pixel has been received or transmitten, 643 depending on the system and other activity in it. 644 * .. _`V4L2-BUF-FLAG-TSTAMP-SRC-SOE`: 645 646 - ``V4L2_BUF_FLAG_TSTAMP_SRC_SOE`` 647 - 0x00010000 648 - Start Of Exposure. The buffer timestamp has been taken when the 649 exposure of the frame has begun. This is only valid for the 650 ``V4L2_BUF_TYPE_VIDEO_CAPTURE`` buffer type. 651 652 653 654.. c:type:: v4l2_memory 655 656enum v4l2_memory 657================ 658 659.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}| 660 661.. flat-table:: 662 :header-rows: 0 663 :stub-columns: 0 664 :widths: 3 1 4 665 666 * - ``V4L2_MEMORY_MMAP`` 667 - 1 668 - The buffer is used for :ref:`memory mapping <mmap>` I/O. 669 * - ``V4L2_MEMORY_USERPTR`` 670 - 2 671 - The buffer is used for :ref:`user pointer <userp>` I/O. 672 * - ``V4L2_MEMORY_OVERLAY`` 673 - 3 674 - [to do] 675 * - ``V4L2_MEMORY_DMABUF`` 676 - 4 677 - The buffer is used for :ref:`DMA shared buffer <dmabuf>` I/O. 678 679 680 681Timecodes 682========= 683 684The struct :c:type:`v4l2_timecode` structure is designed to hold a 685:ref:`smpte12m` or similar timecode. (struct 686struct :c:type:`timeval` timestamps are stored in struct 687:c:type:`v4l2_buffer` field ``timestamp``.) 688 689 690.. c:type:: v4l2_timecode 691 692struct v4l2_timecode 693-------------------- 694 695.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}| 696 697.. flat-table:: 698 :header-rows: 0 699 :stub-columns: 0 700 :widths: 1 1 2 701 702 * - __u32 703 - ``type`` 704 - Frame rate the timecodes are based on, see :ref:`timecode-type`. 705 * - __u32 706 - ``flags`` 707 - Timecode flags, see :ref:`timecode-flags`. 708 * - __u8 709 - ``frames`` 710 - Frame count, 0 ... 23/24/29/49/59, depending on the type of 711 timecode. 712 * - __u8 713 - ``seconds`` 714 - Seconds count, 0 ... 59. This is a binary, not BCD number. 715 * - __u8 716 - ``minutes`` 717 - Minutes count, 0 ... 59. This is a binary, not BCD number. 718 * - __u8 719 - ``hours`` 720 - Hours count, 0 ... 29. This is a binary, not BCD number. 721 * - __u8 722 - ``userbits``\ [4] 723 - The "user group" bits from the timecode. 724 725 726 727.. _timecode-type: 728 729Timecode Types 730-------------- 731 732.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}| 733 734.. flat-table:: 735 :header-rows: 0 736 :stub-columns: 0 737 :widths: 3 1 4 738 739 * - ``V4L2_TC_TYPE_24FPS`` 740 - 1 741 - 24 frames per second, i. e. film. 742 * - ``V4L2_TC_TYPE_25FPS`` 743 - 2 744 - 25 frames per second, i. e. PAL or SECAM video. 745 * - ``V4L2_TC_TYPE_30FPS`` 746 - 3 747 - 30 frames per second, i. e. NTSC video. 748 * - ``V4L2_TC_TYPE_50FPS`` 749 - 4 750 - 751 * - ``V4L2_TC_TYPE_60FPS`` 752 - 5 753 - 754 755 756 757.. _timecode-flags: 758 759Timecode Flags 760-------------- 761 762.. tabularcolumns:: |p{6.6cm}|p{1.4cm}|p{9.5cm}| 763 764.. flat-table:: 765 :header-rows: 0 766 :stub-columns: 0 767 :widths: 3 1 4 768 769 * - ``V4L2_TC_FLAG_DROPFRAME`` 770 - 0x0001 771 - Indicates "drop frame" semantics for counting frames in 29.97 fps 772 material. When set, frame numbers 0 and 1 at the start of each 773 minute, except minutes 0, 10, 20, 30, 40, 50 are omitted from the 774 count. 775 * - ``V4L2_TC_FLAG_COLORFRAME`` 776 - 0x0002 777 - The "color frame" flag. 778 * - ``V4L2_TC_USERBITS_field`` 779 - 0x000C 780 - Field mask for the "binary group flags". 781 * - ``V4L2_TC_USERBITS_USERDEFINED`` 782 - 0x0000 783 - Unspecified format. 784 * - ``V4L2_TC_USERBITS_8BITCHARS`` 785 - 0x0008 786 - 8-bit ISO characters. 787