Lines Matching full:the
9 A stateful video decoder takes complete chunks of the bytestream (e.g. Annex-B
11 display order. The decoder is expected not to require any additional information
12 from the client to process these buffers.
14 Performing software parsing, processing etc. of the stream in the driver in
16 operations are needed, use of the Stateless Video Decoder Interface (in
22 1. The general V4L2 API rules apply if not specified in this document
25 2. The meaning of words "must", "may", "should", etc. is as per `RFC
36 depending on decoder capabilities and following the general V4L2 guidelines.
41 7. Given an ``OUTPUT`` buffer A, then A' represents a buffer on the ``CAPTURE``
50 the destination buffer queue; for decoders, the queue of buffers containing
51 decoded frames; for encoders, the queue of buffers containing an encoded
53 ``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE``; data is captured from the hardware
57 the application communicating with the decoder or encoder implementing
76 processing unit of the HEVC codec (corresponds to macroblock units in
79 Good at sub-partitioning the picture into variable sized structures.
82 the order in which frames are decoded; may differ from display order if the
84 ``OUTPUT`` buffers must be queued by the client in decode order; for
85 encoders ``CAPTURE`` buffers must be returned by the encoder in decode order.
88 data resulting from the decode process; see ``CAPTURE``.
91 the order in which frames must be displayed; for encoders, ``OUTPUT``
92 buffers must be queued by the client in display order; for decoders,
93 ``CAPTURE`` buffers must be returned by the decoder in display order.
104 stream, which clears the list of earlier reference frames (DPBs).
113 popular codecs the size is 16x16 samples (pixels). The HEVC codec uses a
117 the source buffer queue; for decoders, the queue of buffers containing
118 an encoded bytestream; for encoders, the queue of buffers containing raw
120 ``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE``; the hardware is fed with data
130 a point in the bytestream from which decoding may start/continue, without
136 data fed to the decoder or encoder; see ``OUTPUT``.
142 resolution in pixels of source frames being source to the encoder and
143 subject to further cropping to the bounds of visible resolution; relevant to
160 stream resolution of the visible picture, in pixels, to be used for
194 Decoding -> EoS [ label = "EoS mark\nin the stream" ];
217 1. To enumerate the set of coded formats supported by the decoder, the
220 * The full set of supported formats will be returned, regardless of the
222 * Check the flags field of :c:type:`v4l2_fmtdesc` for more information
223 about the decoder's capabilities with respect to each coded format.
224 In particular whether or not the decoder has a full-fledged bytestream
225 parser and if the decoder supports dynamic resolution changes.
227 2. To enumerate the set of supported raw formats, the client may call
230 * Only the formats supported for the format currently active on ``OUTPUT``
234 the client must first set that coded format on ``OUTPUT`` and then
237 3. The client may use :c:func:`VIDIOC_ENUM_FRAMESIZES` to detect supported
242 format will include all possible coded resolutions supported by the
246 will include all possible frame buffer resolutions supported by the
247 decoder for given raw pixel format and the coded format currently set on
250 4. Supported profiles and levels for the coded format currently set on
257 1. Set the coded format on ``OUTPUT`` via :c:func:`VIDIOC_S_FMT`.
268 coded resolution of the stream; required only if it cannot be parsed
269 from the stream for the given coded format; otherwise the decoder will
271 as soon as it can parse the actual coded resolution from the stream.
274 desired size of ``OUTPUT`` buffers; the decoder may adjust it to
285 * The ``CAPTURE`` format will be updated with an appropriate frame buffer
286 resolution instantly based on the width and height returned by
289 after the decoder is done parsing the information from the stream, it will
290 update the ``CAPTURE`` format with new values and signal a source change
291 event, regardless of whether they match the values set by the client or
296 Changing the ``OUTPUT`` format may change the currently set ``CAPTURE``
297 format. How the new ``CAPTURE`` format is determined is up to the decoder
298 and the client must ensure it matches its needs afterwards.
317 the actual number of buffers allocated.
321 The actual number of allocated buffers may differ from the ``count``
322 given. The client must check the updated value of ``count`` after the
325 Alternatively, :c:func:`VIDIOC_CREATE_BUFS` on the ``OUTPUT`` queue can be
345 adjusted to the number of allocated buffers.
349 The actual number of allocated buffers may differ from the ``count``
350 given. The client must check the updated value of ``count`` after the
353 3. Start streaming on the ``OUTPUT`` queue via :c:func:`VIDIOC_STREAMON`.
356 in the stream.** Continue queuing/dequeuing bytestream buffers to/from the
357 ``OUTPUT`` queue via :c:func:`VIDIOC_QBUF` and :c:func:`VIDIOC_DQBUF`. The
358 buffers will be processed and returned to the client in order, until
359 required metadata to configure the ``CAPTURE`` queue are found. This is
360 indicated by the decoder sending a ``V4L2_EVENT_SOURCE_CHANGE`` event with
363 * It is not an error if the first buffer does not contain enough data for
364 this to occur. Processing of the buffers will continue as long as more
367 * If data in a buffer that triggers the event is required to decode the
368 first frame, it will not be returned to the client, until the
369 initialization sequence completes and the frame is decoded.
371 * If the client has not set the coded resolution of the stream on its own,
373 :c:func:`VIDIOC_TRY_FMT` or :c:func:`VIDIOC_REQBUFS` on the ``CAPTURE``
374 queue will not return the real values for the stream until a
380 Any client query issued after the decoder queues the event will return
381 values applying to the just parsed stream, including queue formats,
386 A client capable of acquiring stream parameters from the bytestream on
387 its own may attempt to set the width and height of the ``OUTPUT`` format
388 to non-zero values matching the coded size of the stream, skip this step
389 and continue with the `Capture Setup` sequence. However, it must not
391 selection rectangles and controls, since the decoder has not parsed them
392 from the stream yet. If the values configured by the client do not match
393 those parsed by the decoder, a `Dynamic Resolution Change` will be
400 5. Continue with the `Capture Setup` sequence.
405 1. Call :c:func:`VIDIOC_G_FMT` on the ``CAPTURE`` queue to get format for the
406 destination buffers parsed/decoded from the bytestream.
416 frame buffer resolution for the decoded frames.
429 The value of ``pixelformat`` may be any pixel format supported by the
430 decoder for the current stream. The decoder should choose a
431 preferred/optimal format for the default configuration. For example, a
433 conversion step would be required for the latter.
435 2. **Optional.** Acquire the visible resolution via
449 the visible rectangle; it must fit within the frame buffer resolution
452 * The following selection targets are supported on ``CAPTURE``:
455 corresponds to the coded resolution of the stream.
458 the rectangle covering the part of the ``CAPTURE`` buffer that
460 will be equal to the visible resolution of the stream.
463 the rectangle within the coded resolution to be output to
468 the maximum rectangle within a ``CAPTURE`` buffer, which the cropped
469 frame can be composed into; equal to ``V4L2_SEL_TGT_CROP`` if the
476 the rectangle inside a ``CAPTURE`` buffer into which the cropped
481 the rectangle inside a ``CAPTURE`` buffer which is overwritten by the
482 hardware; equal to ``V4L2_SEL_TGT_COMPOSE`` if the hardware does not
487 The values are guaranteed to be meaningful only after the decoder
488 successfully parses the stream metadata. The client must not rely on the
492 the ``CAPTURE`` queue. Once the stream information is parsed and known, the
498 The decoder will return only formats supported for the currently
499 established coded format, as per the ``OUTPUT`` format and/or stream
501 may be supported by the decoder in general. In other words, the set
502 returned will be a subset of the initial query mentioned in the
509 but after parsing resolution higher than 1920x1088, the decoder will not
513 discovering a resolution change within the same stream may switch
514 the stream into a lower resolution and :c:func:`VIDIOC_ENUM_FMT`
517 4. **Optional.** Set the ``CAPTURE`` format via :c:func:`VIDIOC_S_FMT` on the
518 ``CAPTURE`` queue. The client may choose a different format than
519 selected/suggested by the decoder in :c:func:`VIDIOC_G_FMT`.
530 frame buffer resolution of the decoded stream; typically unchanged from
532 if the hardware supports composition and/or scaling.
534 * Setting the ``CAPTURE`` format will reset the compose selection rectangles
535 to their default values, based on the new resolution, as described in the
538 5. **Optional.** Set the compose rectangle via :c:func:`VIDIOC_S_SELECTION` on
539 the ``CAPTURE`` queue if it is desired and if the decoder has compose and/or
551 the rectangle inside a ``CAPTURE`` buffer into which the cropped
558 the visible rectangle; it must fit within the frame buffer resolution
563 The decoder may adjust the compose rectangle to the nearest
564 supported one to meet codec and hardware requirements. The client needs
565 to check the adjusted rectangle returned by :c:func:`VIDIOC_S_SELECTION`.
567 6. If all the following conditions are met, the client may resume the decoding
570 * ``sizeimage`` of the new format (determined in previous steps) is less
571 than or equal to the size of currently allocated buffers,
573 * the number of buffers currently allocated is greater than or equal to the
575 requirement, the client may use :c:func:`VIDIOC_CREATE_BUFS` to add new
578 In that case, the remaining steps do not apply and the client may resume
579 the decoding by one of the following actions:
581 * if the ``CAPTURE`` queue is streaming, call :c:func:`VIDIOC_DECODER_CMD`
582 with the ``V4L2_DEC_CMD_START`` command,
584 * if the ``CAPTURE`` queue is not streaming, call :c:func:`VIDIOC_STREAMON`
585 on the ``CAPTURE`` queue.
587 However, if the client intends to change the buffer set, to lower
589 the steps below.
591 7. **If the** ``CAPTURE`` **queue is streaming,** keep queuing and dequeuing
592 buffers on the ``CAPTURE`` queue until a buffer marked with the
595 8. **If the** ``CAPTURE`` **queue is streaming,** call :c:func:`VIDIOC_STREAMOFF`
596 on the ``CAPTURE`` queue to stop streaming.
600 The ``OUTPUT`` queue must remain streaming. Calling
601 :c:func:`VIDIOC_STREAMOFF` on it would abort the sequence and trigger a
604 9. **If the** ``CAPTURE`` **queue has buffers allocated,** free the ``CAPTURE``
618 10. Allocate ``CAPTURE`` buffers via :c:func:`VIDIOC_REQBUFS` on the
639 The actual number of allocated buffers may differ from the ``count``
640 given. The client must check the updated value of ``count`` after the
645 To allocate more than the minimum number of buffers (for pipeline
646 depth), the client may query the ``V4L2_CID_MIN_BUFFERS_FOR_CAPTURE``
647 control to get the minimum number of buffers required, and pass the
648 obtained value plus the number of additional buffers needed in the
651 Alternatively, :c:func:`VIDIOC_CREATE_BUFS` on the ``CAPTURE`` queue can be
653 allocating buffers larger than the current ``CAPTURE`` format, future
668 a format representing the maximum framebuffer resolution to be
674 adjusted to the number of allocated buffers.
678 The actual number of allocated buffers may differ from the ``count``
679 given. The client must check the updated value of ``count`` after the
684 To allocate buffers for a format different than parsed from the stream
685 metadata, the client must proceed as follows, before the metadata
688 * set width and height of the ``OUTPUT`` format to desired coded resolution to
689 let the decoder configure the ``CAPTURE`` format appropriately,
691 * query the ``CAPTURE`` format using :c:func:`VIDIOC_G_FMT` and save it
694 The format obtained in the query may be then used with
695 :c:func:`VIDIOC_CREATE_BUFS` in this step to allocate the buffers.
697 11. Call :c:func:`VIDIOC_STREAMON` on the ``CAPTURE`` queue to start decoding
703 This state is reached after the `Capture Setup` sequence finishes successfully.
704 In this state, the client queues and dequeues buffers to both queues via
705 :c:func:`VIDIOC_QBUF` and :c:func:`VIDIOC_DQBUF`, following the standard
708 The content of the source ``OUTPUT`` buffers depends on the active coded pixel
710 the documentation of each format.
712 Both queues operate independently, following the standard behavior of V4L2
713 buffer queues and memory-to-memory devices. In addition, the order of decoded
714 frames dequeued from the ``CAPTURE`` queue may differ from the order of queuing
715 coded frames to the ``OUTPUT`` queue, due to properties of the selected coded
718 The client must not assume any direct relationship between ``CAPTURE``
727 on ``CAPTURE`` (if the encoded data contained more than one frame, or if
728 returning a decoded frame allowed the decoder to return a frame that
729 preceded it in decode, but succeeded it in the display order),
736 * buffers may become available on the ``CAPTURE`` queue without additional
737 buffers queued to ``OUTPUT`` (e.g. during drain or ``EOS``), because of the
738 ``OUTPUT`` buffers queued in the past whose decoding results are only
739 available at later time, due to specifics of the decoding process.
744 originated from, the client can set the ``timestamp`` field of the
745 :c:type:`v4l2_buffer` struct when queuing an ``OUTPUT`` buffer. The
747 will have their ``timestamp`` field set to the same value when dequeued.
749 In addition to the straightforward case of one ``OUTPUT`` buffer producing
750 one ``CAPTURE`` buffer, the following cases are defined:
752 * one ``OUTPUT`` buffer generates multiple ``CAPTURE`` buffers: the same
756 the ``OUTPUT`` buffer queued first will be copied.
758 * the decoding order differs from the display order (i.e. the ``CAPTURE``
759 buffers are out-of-order compared to the ``OUTPUT`` buffers): ``CAPTURE``
760 timestamps will not retain the order of ``OUTPUT`` timestamps.
764 The backing memory of ``CAPTURE`` buffers that are used as reference frames
765 by the stream may be read by the hardware even after they are dequeued.
766 Consequently, the client should avoid writing into this memory while the
770 Similarly, when using a memory type other than ``V4L2_MEMORY_MMAP``, the
772 the same backing memory for as long as the ``CAPTURE`` queue is streaming.
773 The reason for this is that V4L2 buffer indices can be used by drivers to
774 identify frames. Thus, if the backing memory of a reference frame is
775 submitted under a different buffer ID, the driver may misidentify it and
777 of the following frames.
779 During the decoding, the decoder may initiate one of the special sequences, as
780 listed below. The sequences will result in the decoder returning all the
781 ``CAPTURE`` buffers that originated from all the ``OUTPUT`` buffers processed
782 before the sequence started. Last of the buffers will have the
783 ``V4L2_BUF_FLAG_LAST`` flag set. To determine the sequence to follow, the client
787 ``V4L2_EVENT_SRC_CH_RESOLUTION`` is pending, the `Dynamic Resolution
790 * if a ``V4L2_EVENT_EOS`` event is pending, the `End of Stream` sequence needs
793 Some of the sequences can be intermixed with each other and need to be handled
794 as they happen. The exact operation is documented for each sequence.
796 Should a decoding error occur, it will be reported to the client with the level
797 of details depending on the decoder capabilities. Specifically:
799 * the CAPTURE buffer that contains the results of the failed decode operation
800 will be returned with the V4L2_BUF_FLAG_ERROR flag set,
802 * if the decoder is able to precisely report the OUTPUT buffer that triggered
803 the error, such buffer will be returned with the V4L2_BUF_FLAG_ERROR flag
806 In case of a fatal failure that does not allow the decoding to continue, any
807 further operations on corresponding decoder file handle will return the -EIO
808 error code. The client may close the file handle and open a new one, or
809 alternatively reinitialize the instance by stopping streaming on both queues,
810 releasing all buffers and performing the Initialization sequence again.
815 Seek is controlled by the ``OUTPUT`` queue, as it is the source of coded data.
816 The seek does not require any specific operation on the ``CAPTURE`` queue, but
819 1. Stop the ``OUTPUT`` queue to begin the seek sequence via
827 * The decoder will drop all the pending ``OUTPUT`` buffers and they must be
828 treated as returned to the client (following standard semantics).
830 2. Restart the ``OUTPUT`` queue via :c:func:`VIDIOC_STREAMON`.
837 * The decoder will start accepting new source bytestream buffers after the
840 3. Start queuing buffers containing coded data after the seek to the ``OUTPUT``
847 buffers will be processed and returned to the client until a suitable
848 resume point is found. While looking for a resume point, the decoder
853 being made available on the ``CAPTURE`` queue. Drivers must ensure that
859 In case of the H.264/HEVC codec, the client must take care not to seek
860 over a change of SPS/PPS. Even though the target frame could be a
861 keyframe, the stale SPS/PPS inside decoder state would lead to undefined
862 results when decoding. Although the decoder must handle that case without
863 a crash or a fatal decode error, the client must not expect a sensible
866 If the hardware can detect such corrupted decoded frames, then
867 corresponding buffers will be returned to the client with the
868 V4L2_BUF_FLAG_ERROR set. See the `Decoding` section for further
871 4. After a resume point is found, the decoder will start returning ``CAPTURE``
876 A seek may result in the `Dynamic Resolution Change` sequence being
877 initiated, due to the seek target having decoding parameters different from
878 the part of the stream decoded before the seek. The sequence must be handled
883 It is not specified when the ``CAPTURE`` queue starts producing buffers
884 containing decoded data from the ``OUTPUT`` buffers queued after the seek,
885 as it operates independently from the ``OUTPUT`` queue.
887 The decoder may return a number of remaining ``CAPTURE`` buffers containing
888 decoded frames originating from the ``OUTPUT`` buffers queued before the
891 The ``VIDIOC_STREAMOFF`` operation discards any remaining queued
892 ``OUTPUT`` buffers, which means that not all of the ``OUTPUT`` buffers
893 queued before the seek sequence may have matching ``CAPTURE`` buffers
894 produced. For example, given the sequence of operations on the
899 any of the following results on the ``CAPTURE`` queue is allowed:
903 To determine the CAPTURE buffer containing the first decoded frame after the
904 seek, the client may observe the timestamps to match the CAPTURE and OUTPUT
905 buffers or use V4L2_DEC_CMD_STOP and V4L2_DEC_CMD_START to drain the
910 To achieve instantaneous seek, the client may restart streaming on the
916 Streams that include resolution metadata in the bytestream may require switching
917 to a different resolution during the decoding.
921 Not all decoders can detect resolution changes. Those that do set the
922 ``V4L2_FMT_FLAG_DYN_RESOLUTION`` flag for the coded format when
925 The sequence starts when the decoder detects a coded frame with one or more of
926 the following parameters different from those previously established (and
933 * the minimum number of buffers needed for decoding,
935 * bit-depth of the bitstream has been changed.
937 Whenever that happens, the decoder must proceed as follows:
939 1. After encountering a resolution change in the stream, the decoder sends a
945 Any client query issued after the decoder queues the event will return
946 values applying to the stream after the resolution change, including
949 2. The decoder will then process and decode all remaining buffers from before
950 the resolution change point.
952 * The last buffer from before the change must be marked with the
953 ``V4L2_BUF_FLAG_LAST`` flag, similarly to the `Drain` sequence above.
957 The last buffer may be empty (with :c:type:`v4l2_buffer` ``bytesused``
958 = 0) and in that case it must be ignored by the client, as it does not
963 Any attempt to dequeue more ``CAPTURE`` buffers beyond the buffer marked
967 The client must continue the sequence as described below to continue the
970 1. Dequeue the source change event.
974 A source change triggers an implicit decoder drain, similar to the
975 explicit `Drain` sequence. The decoder is stopped after it completes.
976 The decoding process must be resumed with either a pair of calls to
977 :c:func:`VIDIOC_STREAMOFF` and :c:func:`VIDIOC_STREAMON` on the
978 ``CAPTURE`` queue, or a call to :c:func:`VIDIOC_DECODER_CMD` with the
981 2. Continue with the `Capture Setup` sequence.
985 During the resolution change sequence, the ``OUTPUT`` queue must remain
986 streaming. Calling :c:func:`VIDIOC_STREAMOFF` on the ``OUTPUT`` queue would
987 abort the sequence and initiate a seek.
989 In principle, the ``OUTPUT`` queue operates separately from the ``CAPTURE``
990 queue and this remains true for the duration of the entire resolution change
993 The client should, for best performance and simplicity, keep queuing/dequeuing
994 buffers to/from the ``OUTPUT`` queue even while processing this sequence.
1000 ``CAPTURE`` buffers are given to the client, the client must follow the drain
1001 sequence described below. After the drain sequence ends, the client has
1002 received all decoded frames for all ``OUTPUT`` buffers queued before the
1020 The sequence can be only initiated if both ``OUTPUT`` and ``CAPTURE``
1021 queues are streaming. For compatibility reasons, the call to
1022 :c:func:`VIDIOC_DECODER_CMD` will not fail even if any of the queues is
1023 not streaming, but at the same time it will not initiate the `Drain`
1024 sequence and so the steps described below would not be applicable.
1026 2. Any ``OUTPUT`` buffers queued by the client before the
1028 normal. The client must continue to handle both queues independently,
1032 such as the `Dynamic Resolution Change` sequence, before continuing with
1033 the drain sequence,
1035 * queuing and dequeuing ``CAPTURE`` buffers, until a buffer marked with the
1040 The last buffer may be empty (with :c:type:`v4l2_buffer`
1041 ``bytesused`` = 0) and in that case it must be ignored by the client,
1046 Any attempt to dequeue more ``CAPTURE`` buffers beyond the buffer
1050 * dequeuing processed ``OUTPUT`` buffers, until all the buffers queued
1051 before the ``V4L2_DEC_CMD_STOP`` command are dequeued,
1053 * dequeuing the ``V4L2_EVENT_EOS`` event, if the client subscribed to it.
1057 For backwards compatibility, the decoder will signal a ``V4L2_EVENT_EOS``
1058 event when the last frame has been decoded and all frames are ready to be
1059 dequeued. It is a deprecated behavior and the client must not rely on it.
1060 The ``V4L2_BUF_FLAG_LAST`` buffer flag should be used instead.
1062 3. Once all the ``OUTPUT`` buffers queued before the ``V4L2_DEC_CMD_STOP`` call
1063 are dequeued and the last ``CAPTURE`` buffer is dequeued, the decoder is
1065 buffers until the client issues any of the following operations:
1067 * ``V4L2_DEC_CMD_START`` - the decoder will not be reset and will resume
1068 operation normally, with all the state from before the drain,
1070 * a pair of :c:func:`VIDIOC_STREAMOFF` and :c:func:`VIDIOC_STREAMON` on the
1071 ``CAPTURE`` queue - the decoder will resume the operation normally,
1072 however any ``CAPTURE`` buffers still in the queue will be returned to the
1075 * a pair of :c:func:`VIDIOC_STREAMOFF` and :c:func:`VIDIOC_STREAMON` on the
1076 ``OUTPUT`` queue - any pending source buffers will be returned to the
1077 client and the `Seek` sequence will be triggered.
1081 Once the drain sequence is initiated, the client needs to drive it to
1082 completion, as described by the steps above, unless it aborts the process by
1083 issuing :c:func:`VIDIOC_STREAMOFF` on any of the ``OUTPUT`` or ``CAPTURE``
1084 queues. The client is not allowed to issue ``V4L2_DEC_CMD_START`` or
1085 ``V4L2_DEC_CMD_STOP`` again while the drain sequence is in progress and they
1088 Although not mandatory, the availability of decoder commands may be queried
1094 If the decoder encounters an end of stream marking in the stream, the decoder
1095 will initiate the `Drain` sequence, which the client must handle as described
1096 above, skipping the initial :c:func:`VIDIOC_DECODER_CMD`.
1101 Setting formats and allocating buffers trigger changes in the behavior of the
1104 1. Setting the format on the ``OUTPUT`` queue may change the set of formats
1105 supported/advertised on the ``CAPTURE`` queue. In particular, it also means
1106 that the ``CAPTURE`` format may be reset and the client must not rely on the
1109 2. Enumerating formats on the ``CAPTURE`` queue always returns only formats
1110 supported for the current ``OUTPUT`` format.
1112 3. Setting the format on the ``CAPTURE`` queue does not change the list of
1113 formats available on the ``OUTPUT`` queue. An attempt to set a ``CAPTURE``
1114 format that is not supported for the currently selected ``OUTPUT`` format
1115 will result in the decoder adjusting the requested ``CAPTURE`` format to a
1118 4. Enumerating formats on the ``OUTPUT`` queue always returns the full set of
1119 supported coded formats, irrespectively of the current ``CAPTURE`` format.
1121 5. While buffers are allocated on any of the ``OUTPUT`` or ``CAPTURE`` queues,
1122 the client must not change the format on the ``OUTPUT`` queue. Drivers will
1123 return the -EBUSY error code for any such format change attempt.
1125 To summarize, setting formats and allocation must always start with the
1126 ``OUTPUT`` queue and the ``OUTPUT`` queue is the master that governs the
1127 set of supported formats for the ``CAPTURE`` queue.