Le lundi 15 juillet 2019 à 14:12 +0200, Maxime Jourdan a écrit : > On Tue, Jun 11, 2019 at 10:29 AM Hans Verkuil <hverkuil-cisco@xxxxxxxxx> wrote: > > On 6/10/19 9:54 PM, Nicolas Dufresne wrote: > > > Hi Hans, > > > > > > I went through it, and I think we are close to ready. Unfortunately, I > > > believe the SOURCE_CHANGE event is still under specified. There was a > > > post recently to try and add a new flag for changes in color space > > > which is not included here. We are also missing a workflow for changes > > > that don't affect the allocation but will affect the rendering on a > > > display (like colorimetry). Userspace needs to know at which frames > > > these parameter changes in order to signal that to the following > > > processing block. I think we must have a plane for this. > > > > Yes, we need a new flag for the SOURCE_CHANGE event to indicate colorimetry > > changes. That's actually useful for e.g. HDMI receivers as well. > > > > But I don't see why that should make much of a change to the spec: you still > > have to drain the capture queue, the only difference is that you don't need > > to reallocate buffers, you can just restart the decoder. > > > > My intention was to get this spec in first, then extend it once we have a new > > colorimetry change flag. > > > > > Another aspect, I'd like if we could relax a bit the bits about dynamic > > > resolutions, making some space for the "static resolution" cases. > > > Something to keep in mind, these "static resolution" HW might not be > > > able to inform userspace of the display size of the picture, we should > > > check with Maxime what happens with the Amlogic. > > > > I've asked him about that in another email thread: > > > > https://www.mail-archive.com/linux-media@xxxxxxxxxxxxxxx/msg147652.html > > > > Maxime, related to that: can the amlogic detect midstream colorimetry > > changes? Or is that also impossible? > > > > Hi Hans, Nicolas, > > The SOURCE_CHANGE limitations on amlogic are related to older > compression standards. I'm focusing on H264, HEVC, VP9 which will all > be able to properly report resolution changes (and probing at init). > Currently, older codecs such as MPEG 1/2 require userspace to probe > the coded resolution itself and set it to the driver via S_FMT, but > there is no indication from the driver about that. See the series > about the FIXED_RESOLUTION fmt flag for what I had in mind but isn't > that great of a solution.. > > When it comes to colorimetry, I don't believe I saw anything in the > vendor SDK that relates to probing colorspace (e.g bt.709/bt.601 > etc.). > > @Nicolas: is this information embedded in a SEI packet or SPS/PPS when > it comes to H264 ? It seems it a VUI parameter, which is part of the active SPS. > > > > Le lundi 03 juin 2019 à 13:28 +0200, Hans Verkuil a écrit : > > > > From: Tomasz Figa <tfiga@xxxxxxxxxxxx> > > > > > > > > Due to complexity of the video decoding process, the V4L2 drivers of > > > > stateful decoder hardware require specific sequences of V4L2 API calls > > > > to be followed. These include capability enumeration, initialization, > > > > decoding, seek, pause, dynamic resolution change, drain and end of > > > > stream. > > > > > > > > Specifics of the above have been discussed during Media Workshops at > > > > LinuxCon Europe 2012 in Barcelona and then later Embedded Linux > > > > Conference Europe 2014 in Düsseldorf. The de facto Codec API that > > > > originated at those events was later implemented by the drivers we already > > > > have merged in mainline, such as s5p-mfc or coda. > > > > > > > > The only thing missing was the real specification included as a part of > > > > Linux Media documentation. Fix it now and document the decoder part of > > > > the Codec API. > > > > > > > > Signed-off-by: Tomasz Figa <tfiga@xxxxxxxxxxxx> > > > > Signed-off-by: Hans Verkuil <hverkuil-cisco@xxxxxxxxx> > > > > --- > > > > Documentation/media/uapi/v4l/dev-decoder.rst | 1084 +++++++++++++++++ > > > > Documentation/media/uapi/v4l/dev-mem2mem.rst | 8 +- > > > > Documentation/media/uapi/v4l/pixfmt-v4l2.rst | 5 + > > > > Documentation/media/uapi/v4l/v4l2.rst | 10 +- > > > > .../media/uapi/v4l/vidioc-decoder-cmd.rst | 41 +- > > > > 5 files changed, 1132 insertions(+), 16 deletions(-) > > > > create mode 100644 Documentation/media/uapi/v4l/dev-decoder.rst > > > > > > > > diff --git a/Documentation/media/uapi/v4l/dev-decoder.rst b/Documentation/media/uapi/v4l/dev-decoder.rst > > > > new file mode 100644 > > > > index 000000000000..b106f2d97c48 > > > > --- /dev/null > > > > +++ b/Documentation/media/uapi/v4l/dev-decoder.rst > > > > @@ -0,0 +1,1084 @@ > > > > +.. SPDX-License-Identifier: GPL-2.0 > > > > + > > > > +.. _decoder: > > > > + > > > > +************************************************* > > > > +Memory-to-memory Stateful Video Decoder Interface > > > > +************************************************* > > > > + > > > > +A stateful video decoder takes complete chunks of the bitstream (e.g. Annex-B > > > > +H.264/HEVC stream, raw VP8/9 stream) and decodes them into raw video frames in > > > > > > (minor, may ignore) > > > This isn't very precise, do we expect to document this per-format ? I > > > think we should maybe say "a complete frame of the bitstream", that > > > being said, I think stateful CODEC should be allowed to implement the > > > per-slice/per-frame control we are adding to stateless CODEC. Maybe > > > something like "documented complete chunks of bitstream" ? > > > > > > > +display order. The decoder is expected not to require any additional information > > > > +from the client to process these buffers. > > > > + > > > > +Performing software parsing, processing etc. of the stream in the driver in > > > > +order to support this interface is strongly discouraged. In case such > > > > +operations are needed, use of the Stateless Video Decoder Interface (in > > > > +development) is strongly advised. > > > > + > > > > +Conventions and notation used in this document > > > > +============================================== > > > > + > > > > +1. The general V4L2 API rules apply if not specified in this document > > > > + otherwise. > > > > + > > > > +2. The meaning of words "must", "may", "should", etc. is as per `RFC > > > > + 2119 <https://tools.ietf.org/html/rfc2119>`_. > > > > + > > > > +3. All steps not marked "optional" are required. > > > > + > > > > +4. :c:func:`VIDIOC_G_EXT_CTRLS` and :c:func:`VIDIOC_S_EXT_CTRLS` may be used > > > > + interchangeably with :c:func:`VIDIOC_G_CTRL` and :c:func:`VIDIOC_S_CTRL`, > > > > + unless specified otherwise. > > > > + > > > > +5. Single-planar API (see :ref:`planar-apis`) and applicable structures may be > > > > + used interchangeably with multi-planar API, unless specified otherwise, > > > > + depending on decoder capabilities and following the general V4L2 guidelines. > > > > + > > > > +6. i = [a..b]: sequence of integers from a to b, inclusive, i.e. i = > > > > + [0..2]: i = 0, 1, 2. > > > > + > > > > +7. Given an ``OUTPUT`` buffer A, then A’ represents a buffer on the ``CAPTURE`` > > > > + queue containing data that resulted from processing buffer A. > > > > + > > > > +.. _decoder-glossary: > > > > + > > > > +Glossary > > > > +======== > > > > + > > > > +CAPTURE > > > > + the destination buffer queue; for decoders, the queue of buffers containing > > > > + decoded frames; for encoders, the queue of buffers containing an encoded > > > > + bitstream; ``V4L2_BUF_TYPE_VIDEO_CAPTURE`` or > > > > + ``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE``; data is captured from the hardware > > > > + into ``CAPTURE`` buffers. > > > > + > > > > +client > > > > + the application communicating with the decoder or encoder implementing > > > > + this interface. > > > > + > > > > +coded format > > > > + encoded/compressed video bitstream format (e.g. H.264, VP8, etc.); see > > > > + also: raw format. > > > > + > > > > +coded height > > > > + height for given coded resolution. > > > > + > > > > +coded resolution > > > > + stream resolution in pixels aligned to codec and hardware requirements; > > > > + typically visible resolution rounded up to full macroblocks; > > > > + see also: visible resolution. > > > > + > > > > +coded width > > > > + width for given coded resolution. > > > > + > > > > +decode order > > > > + the order in which frames are decoded; may differ from display order if the > > > > + coded format includes a feature of frame reordering; for decoders, > > > > + ``OUTPUT`` buffers must be queued by the client in decode order; for > > > > + encoders ``CAPTURE`` buffers must be returned by the encoder in decode order. > > > > + > > > > +destination > > > > + data resulting from the decode process; see ``CAPTURE``. > > > > + > > > > +display order > > > > + the order in which frames must be displayed; for encoders, ``OUTPUT`` > > > > + buffers must be queued by the client in display order; for decoders, > > > > + ``CAPTURE`` buffers must be returned by the decoder in display order. > > > > + > > > > +DPB > > > > + Decoded Picture Buffer; an H.264/HEVC term for a buffer that stores a decoded > > > > + raw frame available for reference in further decoding steps. > > > > + > > > > +EOS > > > > + end of stream. > > > > + > > > > +IDR > > > > + Instantaneous Decoder Refresh; a type of a keyframe in an H.264/HEVC-encoded > > > > + stream, which clears the list of earlier reference frames (DPBs). > > > > + > > > > +keyframe > > > > + an encoded frame that does not reference frames decoded earlier, i.e. > > > > + can be decoded fully on its own. > > > > + > > > > +macroblock > > > > + a processing unit in image and video compression formats based on linear > > > > + block transforms (e.g. H.264, VP8, VP9); codec-specific, but for most of > > > > + popular codecs the size is 16x16 samples (pixels). > > > > + > > > > +OUTPUT > > > > + the source buffer queue; for decoders, the queue of buffers containing > > > > + an encoded bitstream; for encoders, the queue of buffers containing raw > > > > + frames; ``V4L2_BUF_TYPE_VIDEO_OUTPUT`` or > > > > + ``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE``; the hardware is fed with data > > > > + from ``OUTPUT`` buffers. > > > > + > > > > +PPS > > > > + Picture Parameter Set; a type of metadata entity in an H.264/HEVC bitstream. > > > > + > > > > +raw format > > > > + uncompressed format containing raw pixel data (e.g. YUV, RGB formats). > > > > + > > > > +resume point > > > > + a point in the bitstream from which decoding may start/continue, without > > > > + any previous state/data present, e.g.: a keyframe (VP8/VP9) or > > > > + SPS/PPS/IDR sequence (H.264/HEVC); a resume point is required to start decode > > > > + of a new stream, or to resume decoding after a seek. > > > > + > > > > +source > > > > + data fed to the decoder or encoder; see ``OUTPUT``. > > > > + > > > > +source height > > > > + height in pixels for given source resolution; relevant to encoders only. > > > > + > > > > +source resolution > > > > + resolution in pixels of source frames being source to the encoder and > > > > + subject to further cropping to the bounds of visible resolution; relevant to > > > > + encoders only. > > > > + > > > > +source width > > > > + width in pixels for given source resolution; relevant to encoders only. > > > > + > > > > +SPS > > > > + Sequence Parameter Set; a type of metadata entity in an H.264/HEVC bitstream. > > > > + > > > > +stream metadata > > > > + additional (non-visual) information contained inside encoded bitstream; > > > > + for example: coded resolution, visible resolution, codec profile. > > > > + > > > > +visible height > > > > + height for given visible resolution; display height. > > > > + > > > > +visible resolution > > > > + stream resolution of the visible picture, in pixels, to be used for > > > > + display purposes; must be smaller or equal to coded resolution; > > > > + display resolution. > > > > + > > > > +visible width > > > > + width for given visible resolution; display width. > > > > + > > > > +State machine > > > > +============= > > > > + > > > > +.. kernel-render:: DOT > > > > + :alt: DOT digraph of decoder state machine > > > > + :caption: Decoder state machine > > > > + > > > > + digraph decoder_state_machine { > > > > + node [shape = doublecircle, label="Decoding"] Decoding; > > > > + > > > > + node [shape = circle, label="Initialization"] Initialization; > > > > + node [shape = circle, label="Capture\nsetup"] CaptureSetup; > > > > + node [shape = circle, label="Dynamic\nresolution\nchange"] ResChange; > > > > + node [shape = circle, label="Stopped"] Stopped; > > > > + node [shape = circle, label="Drain"] Drain; > > > > + node [shape = circle, label="Seek"] Seek; > > > > + node [shape = circle, label="End of stream"] EoS; > > > > + > > > > + node [shape = point]; qi > > > > + qi -> Initialization [ label = "open()" ]; > > > > + > > > > + Initialization -> CaptureSetup [ label = "CAPTURE\nformat\nestablished" ]; > > > > + > > > > + CaptureSetup -> Stopped [ label = "CAPTURE\nbuffers\nready" ]; > > > > + > > > > + Decoding -> ResChange [ label = "Stream\nresolution\nchange" ]; > > > > + Decoding -> Drain [ label = "V4L2_DEC_CMD_STOP" ]; > > > > + Decoding -> EoS [ label = "EoS mark\nin the stream" ]; > > > > + Decoding -> Seek [ label = "VIDIOC_STREAMOFF(OUTPUT)" ]; > > > > + Decoding -> Stopped [ label = "VIDIOC_STREAMOFF(CAPTURE)" ]; > > > > + Decoding -> Decoding; > > > > + > > > > + ResChange -> CaptureSetup [ label = "CAPTURE\nformat\nestablished" ]; > > > > + ResChange -> Seek [ label = "VIDIOC_STREAMOFF(OUTPUT)" ]; > > > > + > > > > + EoS -> Drain [ label = "Implicit\ndrain" ]; > > > > + > > > > + Drain -> Stopped [ label = "All CAPTURE\nbuffers dequeued\nor\nVIDIOC_STREAMOFF(CAPTURE)" ]; > > > > + Drain -> Seek [ label = "VIDIOC_STREAMOFF(OUTPUT)" ]; > > > > + > > > > + Seek -> Decoding [ label = "VIDIOC_STREAMON(OUTPUT)" ]; > > > > + Seek -> Initialization [ label = "VIDIOC_REQBUFS(OUTPUT, 0)" ]; > > > > + > > > > + Stopped -> Decoding [ label = "V4L2_DEC_CMD_START\nor\nVIDIOC_STREAMON(CAPTURE)" ]; > > > > + Stopped -> Seek [ label = "VIDIOC_STREAMOFF(OUTPUT)" ]; > > > > + } > > > > + > > > > +Querying capabilities > > > > +===================== > > > > + > > > > +1. To enumerate the set of coded formats supported by the decoder, the > > > > + client may call :c:func:`VIDIOC_ENUM_FMT` on ``OUTPUT``. > > > > + > > > > + * The full set of supported formats will be returned, regardless of the > > > > + format set on ``CAPTURE``. > > > > + > > > > +2. To enumerate the set of supported raw formats, the client may call > > > > + :c:func:`VIDIOC_ENUM_FMT` on ``CAPTURE``. > > > > + > > > > + * Only the formats supported for the format currently active on ``OUTPUT`` > > > > + will be returned. > > > > + > > > > + * In order to enumerate raw formats supported by a given coded format, > > > > + the client must first set that coded format on ``OUTPUT`` and then > > > > + enumerate formats on ``CAPTURE``. > > > > + > > > > +3. The client may use :c:func:`VIDIOC_ENUM_FRAMESIZES` to detect supported > > > > + resolutions for a given format, passing desired pixel format in > > > > + :c:type:`v4l2_frmsizeenum` ``pixel_format``. > > > > + > > > > + * Values returned by :c:func:`VIDIOC_ENUM_FRAMESIZES` for a coded pixel > > > > + format will include all possible coded resolutions supported by the > > > > + decoder for given coded pixel format. > > > > + > > > > + * Values returned by :c:func:`VIDIOC_ENUM_FRAMESIZES` for a raw pixel format > > > > + will include all possible frame buffer resolutions supported by the > > > > + decoder for given raw pixel format and the coded format currently set on > > > > + ``OUTPUT``. > > > > + > > > > +4. Supported profiles and levels for the coded format currently set on > > > > + ``OUTPUT``, if applicable, may be queried using their respective controls > > > > + via :c:func:`VIDIOC_QUERYCTRL`. > > > > + > > > > +Initialization > > > > +============== > > > > + > > > > +1. Set the coded format on ``OUTPUT`` via :c:func:`VIDIOC_S_FMT` > > > > + > > > > + * **Required fields:** > > > > + > > > > + ``type`` > > > > + a ``V4L2_BUF_TYPE_*`` enum appropriate for ``OUTPUT``. > > > > + > > > > + ``pixelformat`` > > > > + a coded pixel format. > > > > + > > > > + ``width``, ``height`` > > > > + coded resolution of the stream; required only if it cannot be parsed > > > > + from the stream for the given coded format; otherwise the decoder will > > > > + use this resolution as a placeholder resolution that will likely change > > > > + as soon as it can parse the actual coded resolution from the stream. > > > > + > > > > + ``sizeimage`` > > > > + desired size of ``OUTPUT`` buffers; the decoder may adjust it to > > > > + match hardware requirements. > > > > + > > > > + other fields > > > > + follow standard semantics. > > > > + > > > > + * **Return fields:** > > > > + > > > > + ``sizeimage`` > > > > + adjusted size of ``OUTPUT`` buffers. > > > > + > > > > + * The ``CAPTURE`` format will be updated with an appropriate frame buffer > > > > + resolution instantly based on the width and height returned by > > > > + :c:func:`VIDIOC_S_FMT`. > > > > + However, for coded formats that include stream resolution information, > > > > + after the decoder is done parsing the information from the stream, it will > > > > + update the ``CAPTURE`` format with new values and signal a source change > > > > + event, regardless of whether they match the values set by the client or > > > > + not. > > > > + > > > > + .. important:: > > > > + > > > > + Changing the ``OUTPUT`` format may change the currently set ``CAPTURE`` > > > > + format. How the new ``CAPTURE`` format is determined is up to the decoder > > > > + and the client must ensure it matches its needs afterwards. > > > > + > > > > +2. Allocate source (bitstream) buffers via :c:func:`VIDIOC_REQBUFS` on > > > > + ``OUTPUT``. > > > > + > > > > + * **Required fields:** > > > > + > > > > + ``count`` > > > > + requested number of buffers to allocate; greater than zero. > > > > + > > > > + ``type`` > > > > + a ``V4L2_BUF_TYPE_*`` enum appropriate for ``OUTPUT``. > > > > + > > > > + ``memory`` > > > > + follows standard semantics. > > > > + > > > > + * **Return fields:** > > > > + > > > > + ``count`` > > > > + the actual number of buffers allocated. > > > > + > > > > + .. warning:: > > > > + > > > > + The actual number of allocated buffers may differ from the ``count`` > > > > + given. The client must check the updated value of ``count`` after the > > > > + call returns. > > > > + > > > > + Alternatively, :c:func:`VIDIOC_CREATE_BUFS` on the ``OUTPUT`` queue can be > > > > + used to have more control over buffer allocation. > > > > + > > > > + * **Required fields:** > > > > + > > > > + ``count`` > > > > + requested number of buffers to allocate; greater than zero. > > > > + > > > > + ``type`` > > > > + a ``V4L2_BUF_TYPE_*`` enum appropriate for ``OUTPUT``. > > > > + > > > > + ``memory`` > > > > + follows standard semantics. > > > > + > > > > + ``format`` > > > > + follows standard semantics. > > > > + > > > > + * **Return fields:** > > > > + > > > > + ``count`` > > > > + adjusted to the number of allocated buffers. > > > > + > > > > + .. warning:: > > > > + > > > > + The actual number of allocated buffers may differ from the ``count`` > > > > + given. The client must check the updated value of ``count`` after the > > > > + call returns. > > > > + > > > > +3. Start streaming on the ``OUTPUT`` queue via :c:func:`VIDIOC_STREAMON`. > > > > + > > > > +4. **This step only applies to coded formats that contain resolution information > > > > + in the stream.** Continue queuing/dequeuing bitstream buffers to/from the > > > > + ``OUTPUT`` queue via :c:func:`VIDIOC_QBUF` and :c:func:`VIDIOC_DQBUF`. The > > > > + buffers will be processed and returned to the client in order, until > > > > + required metadata to configure the ``CAPTURE`` queue are found. This is > > > > + indicated by the decoder sending a ``V4L2_EVENT_SOURCE_CHANGE`` event with > > > > + ``changes`` set to ``V4L2_EVENT_SRC_CH_RESOLUTION``. > > > > + > > > > + * It is not an error if the first buffer does not contain enough data for > > > > + this to occur. Processing of the buffers will continue as long as more > > > > + data is needed. > > > > + > > > > + * If data in a buffer that triggers the event is required to decode the > > > > + first frame, it will not be returned to the client, until the > > > > + initialization sequence completes and the frame is decoded. > > > > + > > > > + * If the client has not set the coded resolution of the stream on its own, > > > > + calling :c:func:`VIDIOC_G_FMT`, :c:func:`VIDIOC_S_FMT`, > > > > + :c:func:`VIDIOC_TRY_FMT` or :c:func:`VIDIOC_REQBUFS` on the ``CAPTURE`` > > > > + queue will not return the real values for the stream until a > > > > + ``V4L2_EVENT_SOURCE_CHANGE`` event is signaled. > > > > + > > > > + .. important:: > > > > + > > > > + Any client query issued after the decoder queues the event will return > > > > + values applying to the just parsed stream, including queue formats, > > > > + selection rectangles and controls. > > > > + > > > > + .. note:: > > > > + > > > > + A client capable of acquiring stream parameters from the bitstream on > > > > + its own may attempt to set the width and height of the ``OUTPUT`` format > > > > + to non-zero values matching the coded size of the stream, skip this step > > > > + and continue with the `Capture setup` sequence. However, it must not > > > > + rely on any driver queries regarding stream parameters, such as > > > > + selection rectangles and controls, since the decoder has not parsed them > > > > + from the stream yet. If the values configured by the client do not match > > > > + those parsed by the decoder, a `Dynamic resolution change` will be > > > > + triggered to reconfigure them. > > > > + > > > > + .. note:: > > > > + > > > > + No decoded frames are produced during this phase. > > > > + > > > > +5. Continue with the `Capture setup` sequence. > > > > + > > > > +Capture setup > > > > +============= > > > > + > > > > +1. Call :c:func:`VIDIOC_G_FMT` on the ``CAPTURE`` queue to get format for the > > > > + destination buffers parsed/decoded from the bitstream. > > > > + > > > > + * **Required fields:** > > > > + > > > > + ``type`` > > > > + a ``V4L2_BUF_TYPE_*`` enum appropriate for ``CAPTURE``. > > > > + > > > > + * **Return fields:** > > > > + > > > > + ``width``, ``height`` > > > > + frame buffer resolution for the decoded frames. > > > > + > > > > + ``pixelformat`` > > > > + pixel format for decoded frames. > > > > + > > > > + ``num_planes`` (for _MPLANE ``type`` only) > > > > + number of planes for pixelformat. > > > > + > > > > + ``sizeimage``, ``bytesperline`` > > > > + as per standard semantics; matching frame buffer format. > > > > + > > > > + .. note:: > > > > + > > > > + The value of ``pixelformat`` may be any pixel format supported by the > > > > + decoder for the current stream. The decoder should choose a > > > > + preferred/optimal format for the default configuration. For example, a > > > > + YUV format may be preferred over an RGB format if an additional > > > > + conversion step would be required for the latter. > > > > + > > > > +2. **Optional.** Acquire the visible resolution via > > > > + :c:func:`VIDIOC_G_SELECTION`. > > > > + > > > > + * **Required fields:** > > > > + > > > > + ``type`` > > > > + a ``V4L2_BUF_TYPE_*`` enum appropriate for ``CAPTURE``. > > > > + > > > > + ``target`` > > > > + set to ``V4L2_SEL_TGT_COMPOSE``. > > > > + > > > > + * **Return fields:** > > > > + > > > > + ``r.left``, ``r.top``, ``r.width``, ``r.height`` > > > > + the visible rectangle; it must fit within the frame buffer resolution > > > > + returned by :c:func:`VIDIOC_G_FMT` on ``CAPTURE``. > > > > + > > > > + * The following selection targets are supported on ``CAPTURE``: > > > > + > > > > + ``V4L2_SEL_TGT_CROP_BOUNDS`` > > > > + corresponds to the coded resolution of the stream. > > > > + > > > > + ``V4L2_SEL_TGT_CROP_DEFAULT`` > > > > + the rectangle covering the part of the ``CAPTURE`` buffer that > > > > + contains meaningful picture data (visible area); width and height > > > > + will be equal to the visible resolution of the stream. > > > > + > > > > + ``V4L2_SEL_TGT_CROP`` > > > > + the rectangle within the coded resolution to be output to > > > > + ``CAPTURE``; defaults to ``V4L2_SEL_TGT_CROP_DEFAULT``; read-only on > > > > + hardware without additional compose/scaling capabilities. > > > > + > > > > + ``V4L2_SEL_TGT_COMPOSE_BOUNDS`` > > > > + the maximum rectangle within a ``CAPTURE`` buffer, which the cropped > > > > + frame can be composed into; equal to ``V4L2_SEL_TGT_CROP`` if the > > > > + hardware does not support compose/scaling. > > > > + > > > > + ``V4L2_SEL_TGT_COMPOSE_DEFAULT`` > > > > + equal to ``V4L2_SEL_TGT_CROP``. > > > > + > > > > + ``V4L2_SEL_TGT_COMPOSE`` > > > > + the rectangle inside a ``CAPTURE`` buffer into which the cropped > > > > + frame is written; defaults to ``V4L2_SEL_TGT_COMPOSE_DEFAULT``; > > > > + read-only on hardware without additional compose/scaling capabilities. > > > > + > > > > + ``V4L2_SEL_TGT_COMPOSE_PADDED`` > > > > + the rectangle inside a ``CAPTURE`` buffer which is overwritten by the > > > > + hardware; equal to ``V4L2_SEL_TGT_COMPOSE`` if the hardware does not > > > > + write padding pixels. > > > > + > > > > + .. warning:: > > > > + > > > > + The values are guaranteed to be meaningful only after the decoder > > > > + successfully parses the stream metadata. The client must not rely on the > > > > + query before that happens. > > > > + > > > > +3. **Optional.** Enumerate ``CAPTURE`` formats via :c:func:`VIDIOC_ENUM_FMT` on > > > > + the ``CAPTURE`` queue. Once the stream information is parsed and known, the > > > > + client may use this ioctl to discover which raw formats are supported for > > > > + given stream and select one of them via :c:func:`VIDIOC_S_FMT`. > > > > + > > > > + .. important:: > > > > + > > > > + The decoder will return only formats supported for the currently > > > > + established coded format, as per the ``OUTPUT`` format and/or stream > > > > + metadata parsed in this initialization sequence, even if more formats > > > > + may be supported by the decoder in general. In other words, the set > > > > + returned will be a subset of the initial query mentioned in the > > > > + `Querying capabilities` section. > > > > + > > > > + For example, a decoder may support YUV and RGB formats for resolutions > > > > + 1920x1088 and lower, but only YUV for higher resolutions (due to > > > > + hardware limitations). After parsing a resolution of 1920x1088 or lower, > > > > + :c:func:`VIDIOC_ENUM_FMT` may return a set of YUV and RGB pixel formats, > > > > + but after parsing resolution higher than 1920x1088, the decoder will not > > > > + return RGB, unsupported for this resolution. > > > > + > > > > + However, subsequent resolution change event triggered after > > > > + discovering a resolution change within the same stream may switch > > > > + the stream into a lower resolution and :c:func:`VIDIOC_ENUM_FMT` > > > > + would return RGB formats again in that case. > > > > + > > > > +4. **Optional.** Set the ``CAPTURE`` format via :c:func:`VIDIOC_S_FMT` on the > > > > + ``CAPTURE`` queue. The client may choose a different format than > > > > + selected/suggested by the decoder in :c:func:`VIDIOC_G_FMT`. > > > > + > > > > + * **Required fields:** > > > > + > > > > + ``type`` > > > > + a ``V4L2_BUF_TYPE_*`` enum appropriate for ``CAPTURE``. > > > > + > > > > + ``pixelformat`` > > > > + a raw pixel format. > > > > + > > > > + * Setting the ``CAPTURE`` format will reset the compose selection rectangles > > > > + to their default values, based on the new resolution, as described in the > > > > + previous step. > > > > + > > > > +5. **Optional.** Set the compose rectangle via :c:func:`VIDIOC_S_SELECTION` on > > > > + the ``CAPTURE`` queue if it is desired and if the decoder has compose and/or > > > > + scaling capabilities. > > > > + > > > > + * **Required fields:** > > > > + > > > > + ``type`` > > > > + a ``V4L2_BUF_TYPE_*`` enum appropriate for ``CAPTURE``. > > > > + > > > > + ``target`` > > > > + set to ``V4L2_SEL_TGT_COMPOSE``. > > > > + > > > > + ``r.left``, ``r.top``, ``r.width``, ``r.height`` > > > > + the rectangle inside a ``CAPTURE`` buffer into which the cropped > > > > + frame is written; defaults to ``V4L2_SEL_TGT_COMPOSE_DEFAULT``; > > > > + read-only on hardware without additional compose/scaling capabilities. > > > > + > > > > + * **Return fields:** > > > > + > > > > + ``r.left``, ``r.top``, ``r.width``, ``r.height`` > > > > + the visible rectangle; it must fit within the frame buffer resolution > > > > + returned by :c:func:`VIDIOC_G_FMT` on ``CAPTURE``. > > > > + > > > > + .. warning:: > > > > + > > > > + The decoder may adjust the compose rectangle to the nearest > > > > + supported one to meet codec and hardware requirements. The client needs > > > > + to check the adjusted rectangle returned by :c:func:`VIDIOC_S_SELECTION`. > > > > + > > > > +6. If all the following conditions are met, the client may resume the decoding > > > > + instantly: > > > > + > > > > + * ``sizeimage`` of the new format (determined in previous steps) is less > > > > + than or equal to the size of currently allocated buffers, > > > > + > > > > + * the number of buffers currently allocated is greater than or equal to the > > > > + minimum number of buffers acquired in previous steps. To fulfill this > > > > + requirement, the client may use :c:func:`VIDIOC_CREATE_BUFS` to add new > > > > + buffers. > > > > + > > > > + In that case, the remaining steps do not apply and the client may resume > > > > + the decoding by one of the following actions: > > > > + > > > > + * if the ``CAPTURE`` queue is streaming, call :c:func:`VIDIOC_DECODER_CMD` > > > > + with the ``V4L2_DEC_CMD_START`` command, > > > > + > > > > + * if the ``CAPTURE`` queue is not streaming, call :c:func:`VIDIOC_STREAMON` > > > > + on the ``CAPTURE`` queue. > > > > + > > > > + However, if the client intends to change the buffer set, to lower > > > > + memory usage or for any other reasons, it may be achieved by following > > > > + the steps below. > > > > + > > > > +7. **If the** ``CAPTURE`` **queue is streaming,** keep queuing and dequeuing > > > > + buffers on the ``CAPTURE`` queue until a buffer marked with the > > > > + ``V4L2_BUF_FLAG_LAST`` flag is dequeued. > > > > + > > > > +8. **If the** ``CAPTURE`` **queue is streaming,** call :c:func:`VIDIOC_STREAMOFF` > > > > + on the ``CAPTURE`` queue to stop streaming. > > > > + > > > > + .. warning:: > > > > + > > > > + The ``OUTPUT`` queue must remain streaming. Calling > > > > + :c:func:`VIDIOC_STREAMOFF` on it would abort the sequence and trigger a > > > > + seek. > > > > + > > > > +9. **If the** ``CAPTURE`` **queue has buffers allocated,** free the ``CAPTURE`` > > > > + buffers using :c:func:`VIDIOC_REQBUFS`. > > > > + > > > > + * **Required fields:** > > > > + > > > > + ``count`` > > > > + set to 0. > > > > + > > > > + ``type`` > > > > + a ``V4L2_BUF_TYPE_*`` enum appropriate for ``CAPTURE``. > > > > + > > > > + ``memory`` > > > > + follows standard semantics. > > > > + > > > > +10. Allocate ``CAPTURE`` buffers via :c:func:`VIDIOC_REQBUFS` on the > > > > + ``CAPTURE`` queue. > > > > + > > > > + * **Required fields:** > > > > + > > > > + ``count`` > > > > + requested number of buffers to allocate; greater than zero. > > > > + > > > > + ``type`` > > > > + a ``V4L2_BUF_TYPE_*`` enum appropriate for ``CAPTURE``. > > > > + > > > > + ``memory`` > > > > + follows standard semantics. > > > > + > > > > + * **Return fields:** > > > > + > > > > + ``count`` > > > > + actual number of buffers allocated. > > > > + > > > > + .. warning:: > > > > + > > > > + The actual number of allocated buffers may differ from the ``count`` > > > > + given. The client must check the updated value of ``count`` after the > > > > + call returns. > > > > + > > > > + .. note:: > > > > + > > > > + To allocate more than the minimum number of buffers (for pipeline > > > > + depth), the client may query the ``V4L2_CID_MIN_BUFFERS_FOR_CAPTURE`` > > > > + control to get the minimum number of buffers required, and pass the > > > > + obtained value plus the number of additional buffers needed in the > > > > + ``count`` field to :c:func:`VIDIOC_REQBUFS`. > > > > + > > > > + Alternatively, :c:func:`VIDIOC_CREATE_BUFS` on the ``CAPTURE`` queue can be > > > > + used to have more control over buffer allocation. For example, by > > > > + allocating buffers larger than the current ``CAPTURE`` format, future > > > > + resolution changes can be accommodated. > > > > + > > > > + * **Required fields:** > > > > + > > > > + ``count`` > > > > + requested number of buffers to allocate; greater than zero. > > > > + > > > > + ``type`` > > > > + a ``V4L2_BUF_TYPE_*`` enum appropriate for ``CAPTURE``. > > > > + > > > > + ``memory`` > > > > + follows standard semantics. > > > > + > > > > + ``format`` > > > > + a format representing the maximum framebuffer resolution to be > > > > + accommodated by newly allocated buffers. > > > > + > > > > + * **Return fields:** > > > > + > > > > + ``count`` > > > > + adjusted to the number of allocated buffers. > > > > + > > > > + .. warning:: > > > > + > > > > + The actual number of allocated buffers may differ from the ``count`` > > > > + given. The client must check the updated value of ``count`` after the > > > > + call returns. > > > > + > > > > + .. note:: > > > > + > > > > + To allocate buffers for a format different than parsed from the stream > > > > + metadata, the client must proceed as follows, before the metadata > > > > + parsing is initiated: > > > > + > > > > + * set width and height of the ``OUTPUT`` format to desired coded resolution to > > > > + let the decoder configure the ``CAPTURE`` format appropriately, > > > > + > > > > + * query the ``CAPTURE`` format using :c:func:`VIDIOC_G_FMT` and save it > > > > + until this step. > > > > + > > > > + The format obtained in the query may be then used with > > > > + :c:func:`VIDIOC_CREATE_BUFS` in this step to allocate the buffers. > > > > + > > > > +11. Call :c:func:`VIDIOC_STREAMON` on the ``CAPTURE`` queue to start decoding > > > > + frames. > > > > + > > > > +Decoding > > > > +======== > > > > + > > > > +This state is reached after the `Capture setup` sequence finishes successfully. > > > > +In this state, the client queues and dequeues buffers to both queues via > > > > +:c:func:`VIDIOC_QBUF` and :c:func:`VIDIOC_DQBUF`, following the standard > > > > +semantics. > > > > + > > > > +The content of the source ``OUTPUT`` buffers depends on the active coded pixel > > > > +format and may be affected by codec-specific extended controls, as stated in > > > > +the documentation of each format. > > > > + > > > > +Both queues operate independently, following the standard behavior of V4L2 > > > > +buffer queues and memory-to-memory devices. In addition, the order of decoded > > > > +frames dequeued from the ``CAPTURE`` queue may differ from the order of queuing > > > > +coded frames to the ``OUTPUT`` queue, due to properties of the selected coded > > > > +format, e.g. frame reordering. > > > > + > > > > +The client must not assume any direct relationship between ``CAPTURE`` > > > > +and ``OUTPUT`` buffers and any specific timing of buffers becoming > > > > +available to dequeue. Specifically: > > > > + > > > > +* a buffer queued to ``OUTPUT`` may result in no buffers being produced > > > > + on ``CAPTURE`` (e.g. if it does not contain encoded data, or if only > > > > + metadata syntax structures are present in it), > > > > + > > > > +* a buffer queued to ``OUTPUT`` may result in more than one buffer produced > > > > + on ``CAPTURE`` (if the encoded data contained more than one frame, or if > > > > + returning a decoded frame allowed the decoder to return a frame that > > > > + preceded it in decode, but succeeded it in the display order), > > > > + > > > > +* a buffer queued to ``OUTPUT`` may result in a buffer being produced on > > > > + ``CAPTURE`` later into decode process, and/or after processing further > > > > + ``OUTPUT`` buffers, or be returned out of order, e.g. if display > > > > + reordering is used, > > > > + > > > > +* buffers may become available on the ``CAPTURE`` queue without additional > > > > + buffers queued to ``OUTPUT`` (e.g. during drain or ``EOS``), because of the > > > > + ``OUTPUT`` buffers queued in the past whose decoding results are only > > > > + available at later time, due to specifics of the decoding process. > > > > + > > > > +.. note:: > > > > + > > > > + To allow matching decoded ``CAPTURE`` buffers with ``OUTPUT`` buffers they > > > > + originated from, the client can set the ``timestamp`` field of the > > > > + :c:type:`v4l2_buffer` struct when queuing an ``OUTPUT`` buffer. The > > > > + ``CAPTURE`` buffer(s), which resulted from decoding that ``OUTPUT`` buffer > > > > + will have their ``timestamp`` field set to the same value when dequeued. > > > > + > > > > + In addition to the straightforward case of one ``OUTPUT`` buffer producing > > > > + one ``CAPTURE`` buffer, the following cases are defined: > > > > + > > > > + * one ``OUTPUT`` buffer generates multiple ``CAPTURE`` buffers: the same > > > > + ``OUTPUT`` timestamp will be copied to multiple ``CAPTURE`` buffers. > > > > + > > > > + * multiple ``OUTPUT`` buffers generate one ``CAPTURE`` buffer: timestamp of > > > > + the ``OUTPUT`` buffer queued last will be copied. > > > > + > > > > + * the decoding order differs from the display order (i.e. the ``CAPTURE`` > > > > + buffers are out-of-order compared to the ``OUTPUT`` buffers): ``CAPTURE`` > > > > + timestamps will not retain the order of ``OUTPUT`` timestamps. > > > > + > > > > +During the decoding, the decoder may initiate one of the special sequences, as > > > > +listed below. The sequences will result in the decoder returning all the > > > > +``CAPTURE`` buffers that originated from all the ``OUTPUT`` buffers processed > > > > +before the sequence started. Last of the buffers will have the > > > > +``V4L2_BUF_FLAG_LAST`` flag set. To determine the sequence to follow, the client > > > > +must check if there is any pending event and: > > > > + > > > > +* if a ``V4L2_EVENT_SOURCE_CHANGE`` event is pending, the `Dynamic resolution > > > > + change` sequence needs to be followed, > > > > + > > > > +* if a ``V4L2_EVENT_EOS`` event is pending, the `End of stream` sequence needs > > > > + to be followed. > > > > + > > > > +Some of the sequences can be intermixed with each other and need to be handled > > > > +as they happen. The exact operation is documented for each sequence. > > > > + > > > > +Should a decoding error occur, it will be reported to the client with the level > > > > +of details depending on the decoder capabilities. Specifically: > > > > + > > > > +* the CAPTURE buffer that contains the results of the failed decode operation > > > > + will be returned with the V4L2_BUF_FLAG_ERROR flag set, > > > > + > > > > +* if the decoder is able to precisely report the OUTPUT buffer that triggered > > > > + the error, such buffer will be returned with the V4L2_BUF_FLAG_ERROR flag > > > > + set. > > > > + > > > > +In case of a fatal failure that does not allow the decoding to continue, any > > > > +further operations on corresponding decoder file handle will return the -EIO > > > > +error code. The client may close the file handle and open a new one, or > > > > +alternatively reinitialize the instance by stopping streaming on both queues, > > > > +releasing all buffers and performing the Initialization sequence again. > > > > + > > > > +Seek > > > > +==== > > > > + > > > > +Seek is controlled by the ``OUTPUT`` queue, as it is the source of coded data. > > > > +The seek does not require any specific operation on the ``CAPTURE`` queue, but > > > > +it may be affected as per normal decoder operation. > > > > + > > > > +1. Stop the ``OUTPUT`` queue to begin the seek sequence via > > > > + :c:func:`VIDIOC_STREAMOFF`. > > > > + > > > > + * **Required fields:** > > > > + > > > > + ``type`` > > > > + a ``V4L2_BUF_TYPE_*`` enum appropriate for ``OUTPUT``. > > > > + > > > > + * The decoder will drop all the pending ``OUTPUT`` buffers and they must be > > > > + treated as returned to the client (following standard semantics). > > > > + > > > > +2. Restart the ``OUTPUT`` queue via :c:func:`VIDIOC_STREAMON` > > > > + > > > > + * **Required fields:** > > > > + > > > > + ``type`` > > > > + a ``V4L2_BUF_TYPE_*`` enum appropriate for ``OUTPUT``. > > > > + > > > > + * The decoder will start accepting new source bitstream buffers after the > > > > + call returns. > > > > + > > > > +3. Start queuing buffers containing coded data after the seek to the ``OUTPUT`` > > > > + queue until a suitable resume point is found. > > > > + > > > > + .. note:: > > > > + > > > > + There is no requirement to begin queuing coded data starting exactly > > > > + from a resume point (e.g. SPS or a keyframe). Any queued ``OUTPUT`` > > > > + buffers will be processed and returned to the client until a suitable > > > > + resume point is found. While looking for a resume point, the decoder > > > > + should not produce any decoded frames into ``CAPTURE`` buffers. > > > > + > > > > + Some hardware is known to mishandle seeks to a non-resume point. Such an > > > > + operation may result in an unspecified number of corrupted decoded frames > > > > + being made available on the ``CAPTURE`` queue. Drivers must ensure that > > > > + no fatal decoding errors or crashes occur, and implement any necessary > > > > + handling and workarounds for hardware issues related to seek operations. > > > > + > > > > + .. warning:: > > > > + > > > > + In case of the H.264/HEVC codec, the client must take care not to seek > > > > + over a change of SPS/PPS. Even though the target frame could be a > > > > + keyframe, the stale SPS/PPS inside decoder state would lead to undefined > > > > + results when decoding. Although the decoder must handle that case without > > > > + a crash or a fatal decode error, the client must not expect a sensible > > > > + decode output. > > > > + > > > > + If the hardware can detect such corrupted decoded frames, then > > > > + corresponding buffers will be returned to the client with the > > > > + V4L2_BUF_FLAG_ERROR set. See the `Decoding` section for further > > > > + description of decode error reporting. > > > > + > > > > +4. After a resume point is found, the decoder will start returning ``CAPTURE`` > > > > + buffers containing decoded frames. > > > > + > > > > +.. important:: > > > > + > > > > + A seek may result in the `Dynamic resolution change` sequence being > > > > + initiated, due to the seek target having decoding parameters different from > > > > + the part of the stream decoded before the seek. The sequence must be handled > > > > + as per normal decoder operation. > > > > + > > > > +.. warning:: > > > > + > > > > + It is not specified when the ``CAPTURE`` queue starts producing buffers > > > > + containing decoded data from the ``OUTPUT`` buffers queued after the seek, > > > > + as it operates independently from the ``OUTPUT`` queue. > > > > + > > > > + The decoder may return a number of remaining ``CAPTURE`` buffers containing > > > > + decoded frames originating from the ``OUTPUT`` buffers queued before the > > > > + seek sequence is performed. > > > > + > > > > + The ``VIDIOC_STREAMOFF`` operation discards any remaining queued > > > > + ``OUTPUT`` buffers, which means that not all of the ``OUTPUT`` buffers > > > > + queued before the seek sequence may have matching ``CAPTURE`` buffers > > > > + produced. For example, given the sequence of operations on the > > > > + ``OUTPUT`` queue: > > > > + > > > > + QBUF(A), QBUF(B), STREAMOFF(), STREAMON(), QBUF(G), QBUF(H), > > > > + > > > > + any of the following results on the ``CAPTURE`` queue is allowed: > > > > + > > > > + {A’, B’, G’, H’}, {A’, G’, H’}, {G’, H’}. > > > > + > > > > + To determine the CAPTURE buffer containing the first decoded frame after the > > > > + seek, the client may observe the timestamps to match the CAPTURE and OUTPUT > > > > + buffers or use V4L2_DEC_CMD_STOP and V4L2_DEC_CMD_START to drain the > > > > + decoder. > > > > + > > > > +.. note:: > > > > + > > > > + To achieve instantaneous seek, the client may restart streaming on the > > > > + ``CAPTURE`` queue too to discard decoded, but not yet dequeued buffers. > > > > + > > > > +Dynamic resolution change > > > > +========================= > > > > + > > > > +Streams that include resolution metadata in the bitstream may require switching > > > > +to a different resolution during the decoding. > > > > + > > > > +The sequence starts when the decoder detects a coded frame with one or more of > > > > +the following parameters different from those previously established (and > > > > +reflected by corresponding queries): > > > > + > > > > +* coded resolution (``OUTPUT`` width and height), > > > > + > > > > +* visible resolution (selection rectangles), > > > > + > > > > +* the minimum number of buffers needed for decoding. > > > > + > > > > +Whenever that happens, the decoder must proceed as follows: > > > > + > > > > +1. After encountering a resolution change in the stream, the decoder sends a > > > > + ``V4L2_EVENT_SOURCE_CHANGE`` event with ``changes`` set to > > > > + ``V4L2_EVENT_SRC_CH_RESOLUTION``. > > > > > > What about a format changes that does now affect the resolution, like a > > > pixel format change ? Also, what about changes that don't require a > > > > A pixel format change always implies a resolution change. > > > > > reallocation ? Like a change in the colorimetry parameters ? I don't > > > think the spec need to initially cover it all, but we need to make sure > > > there is a mechanism for userspace to know at which frames to read back > > > the new format (G_FMT). Maybe we need both an event and a buffer flag > > > to mark it ? > > > > After a SOURCE_CHANGE event is received, G_FMT returns the *new* format, > > including colorimetry. This will become the active format once the drain > > operation finished. > > > > If that's not clear from the spec, then I need to improve it. > > > > Regards, > > > > Hans > > > > > > + > > > > + .. important:: > > > > + > > > > + Any client query issued after the decoder queues the event will return > > > > + values applying to the stream after the resolution change, including > > > > + queue formats, selection rectangles and controls. > > > > + > > > > +2. The decoder will then process and decode all remaining buffers from before > > > > + the resolution change point. > > > > + > > > > + * The last buffer from before the change must be marked with the > > > > + ``V4L2_BUF_FLAG_LAST`` flag, similarly to the `Drain` sequence above. > > > > + > > > > + .. warning:: > > > > + > > > > + The last buffer may be empty (with :c:type:`v4l2_buffer` ``bytesused`` > > > > + = 0) and in that case it must be ignored by the client, as it does not > > > > + contain a decoded frame. > > > > + > > > > + .. note:: > > > > + > > > > + Any attempt to dequeue more ``CAPTURE`` buffers beyond the buffer marked > > > > + with ``V4L2_BUF_FLAG_LAST`` will result in a -EPIPE error from > > > > + :c:func:`VIDIOC_DQBUF`. > > > > + > > > > +The client must continue the sequence as described below to continue the > > > > +decoding process. > > > > + > > > > +1. Dequeue the source change event. > > > > + > > > > + .. important:: > > > > + > > > > + A source change triggers an implicit decoder drain, similar to the > > > > + explicit `Drain` sequence. The decoder is stopped after it completes. > > > > + The decoding process must be resumed with either a pair of calls to > > > > + :c:func:`VIDIOC_STREAMOFF` and :c:func:`VIDIOC_STREAMON` on the > > > > + ``CAPTURE`` queue, or a call to :c:func:`VIDIOC_DECODER_CMD` with the > > > > + ``V4L2_DEC_CMD_START`` command. > > > > + > > > > +2. Continue with the `Capture setup` sequence. > > > > + > > > > +.. note:: > > > > + > > > > + During the resolution change sequence, the ``OUTPUT`` queue must remain > > > > + streaming. Calling :c:func:`VIDIOC_STREAMOFF` on the ``OUTPUT`` queue would > > > > + abort the sequence and initiate a seek. > > > > + > > > > + In principle, the ``OUTPUT`` queue operates separately from the ``CAPTURE`` > > > > + queue and this remains true for the duration of the entire resolution change > > > > + sequence as well. > > > > + > > > > + The client should, for best performance and simplicity, keep queuing/dequeuing > > > > + buffers to/from the ``OUTPUT`` queue even while processing this sequence. > > > > + > > > > +Drain > > > > +===== > > > > + > > > > +To ensure that all queued ``OUTPUT`` buffers have been processed and related > > > > +``CAPTURE`` buffers are given to the client, the client must follow the drain > > > > +sequence described below. After the drain sequence ends, the client has > > > > +received all decoded frames for all ``OUTPUT`` buffers queued before the > > > > +sequence was started. > > > > + > > > > +1. Begin drain by issuing :c:func:`VIDIOC_DECODER_CMD`. > > > > + > > > > + * **Required fields:** > > > > + > > > > + ``cmd`` > > > > + set to ``V4L2_DEC_CMD_STOP``. > > > > + > > > > + ``flags`` > > > > + set to 0. > > > > + > > > > + ``pts`` > > > > + set to 0. > > > > + > > > > + .. warning:: > > > > + > > > > + The sequence can be only initiated if both ``OUTPUT`` and ``CAPTURE`` > > > > + queues are streaming. For compatibility reasons, the call to > > > > + :c:func:`VIDIOC_DECODER_CMD` will not fail even if any of the queues is > > > > + not streaming, but at the same time it will not initiate the `Drain` > > > > + sequence and so the steps described below would not be applicable. > > > > + > > > > +2. Any ``OUTPUT`` buffers queued by the client before the > > > > + :c:func:`VIDIOC_DECODER_CMD` was issued will be processed and decoded as > > > > + normal. The client must continue to handle both queues independently, > > > > + similarly to normal decode operation. This includes: > > > > + > > > > + * handling any operations triggered as a result of processing those buffers, > > > > + such as the `Dynamic resolution change` sequence, before continuing with > > > > + the drain sequence, > > > > + > > > > + * queuing and dequeuing ``CAPTURE`` buffers, until a buffer marked with the > > > > + ``V4L2_BUF_FLAG_LAST`` flag is dequeued, > > > > + > > > > + .. warning:: > > > > + > > > > + The last buffer may be empty (with :c:type:`v4l2_buffer` > > > > + ``bytesused`` = 0) and in that case it must be ignored by the client, > > > > + as it does not contain a decoded frame. > > > > + > > > > + .. note:: > > > > + > > > > + Any attempt to dequeue more ``CAPTURE`` buffers beyond the buffer > > > > + marked with ``V4L2_BUF_FLAG_LAST`` will result in a -EPIPE error from > > > > + :c:func:`VIDIOC_DQBUF`. > > > > + > > > > + * dequeuing processed ``OUTPUT`` buffers, until all the buffers queued > > > > + before the ``V4L2_DEC_CMD_STOP`` command are dequeued, > > > > + > > > > + * dequeuing the ``V4L2_EVENT_EOS`` event, if the client subscribed to it. > > > > + > > > > + .. note:: > > > > + > > > > + For backwards compatibility, the decoder will signal a ``V4L2_EVENT_EOS`` > > > > + event when the last frame has been decoded and all frames are ready to be > > > > + dequeued. It is a deprecated behavior and the client must not rely on it. > > > > + The ``V4L2_BUF_FLAG_LAST`` buffer flag should be used instead. > > > > + > > > > +3. Once all the ``OUTPUT`` buffers queued before the ``V4L2_DEC_CMD_STOP`` call > > > > + are dequeued and the last ``CAPTURE`` buffer is dequeued, the decoder is > > > > + stopped and it will accept, but not process, any newly queued ``OUTPUT`` > > > > + buffers until the client issues any of the following operations: > > > > + > > > > + * ``V4L2_DEC_CMD_START`` - the decoder will not be reset and will resume > > > > + operation normally, with all the state from before the drain, > > > > + > > > > + * a pair of :c:func:`VIDIOC_STREAMOFF` and :c:func:`VIDIOC_STREAMON` on the > > > > + ``CAPTURE`` queue - the decoder will resume the operation normally, > > > > + however any ``CAPTURE`` buffers still in the queue will be returned to the > > > > + client, > > > > + > > > > + * a pair of :c:func:`VIDIOC_STREAMOFF` and :c:func:`VIDIOC_STREAMON` on the > > > > + ``OUTPUT`` queue - any pending source buffers will be returned to the > > > > + client and the `Seek` sequence will be triggered. > > > > + > > > > +.. note:: > > > > + > > > > + Once the drain sequence is initiated, the client needs to drive it to > > > > + completion, as described by the steps above, unless it aborts the process by > > > > + issuing :c:func:`VIDIOC_STREAMOFF` on any of the ``OUTPUT`` or ``CAPTURE`` > > > > + queues. The client is not allowed to issue ``V4L2_DEC_CMD_START`` or > > > > + ``V4L2_DEC_CMD_STOP`` again while the drain sequence is in progress and they > > > > + will fail with -EBUSY error code if attempted. > > > > + > > > > + Although mandatory, the availability of decoder commands may be queried > > > > + using :c:func:`VIDIOC_TRY_DECODER_CMD`. > > > > + > > > > +End of stream > > > > +============= > > > > + > > > > +If the decoder encounters an end of stream marking in the stream, the decoder > > > > +will initiate the `Drain` sequence, which the client must handle as described > > > > +above, skipping the initial :c:func:`VIDIOC_DECODER_CMD`. > > > > + > > > > +Commit points > > > > +============= > > > > + > > > > +Setting formats and allocating buffers trigger changes in the behavior of the > > > > +decoder. > > > > + > > > > +1. Setting the format on the ``OUTPUT`` queue may change the set of formats > > > > + supported/advertised on the ``CAPTURE`` queue. In particular, it also means > > > > + that the ``CAPTURE`` format may be reset and the client must not rely on the > > > > + previously set format being preserved. > > > > + > > > > +2. Enumerating formats on the ``CAPTURE`` queue always returns only formats > > > > + supported for the current ``OUTPUT`` format. > > > > + > > > > +3. Setting the format on the ``CAPTURE`` queue does not change the list of > > > > + formats available on the ``OUTPUT`` queue. An attempt to set a ``CAPTURE`` > > > > + format that is not supported for the currently selected ``OUTPUT`` format > > > > + will result in the decoder adjusting the requested ``CAPTURE`` format to a > > > > + supported one. > > > > + > > > > +4. Enumerating formats on the ``OUTPUT`` queue always returns the full set of > > > > + supported coded formats, irrespectively of the current ``CAPTURE`` format. > > > > + > > > > +5. While buffers are allocated on any of the ``OUTPUT`` or ``CAPTURE`` queues, > > > > + the client must not change the format on the ``OUTPUT`` queue. Drivers will > > > > + return the -EBUSY error code for any such format change attempt. > > > > + > > > > +To summarize, setting formats and allocation must always start with the > > > > +``OUTPUT`` queue and the ``OUTPUT`` queue is the master that governs the > > > > +set of supported formats for the ``CAPTURE`` queue. > > > > diff --git a/Documentation/media/uapi/v4l/dev-mem2mem.rst b/Documentation/media/uapi/v4l/dev-mem2mem.rst > > > > index 67a980818dc8..caa05f5f6380 100644 > > > > --- a/Documentation/media/uapi/v4l/dev-mem2mem.rst > > > > +++ b/Documentation/media/uapi/v4l/dev-mem2mem.rst > > > > @@ -39,4 +39,10 @@ file handle is visible through another file handle). > > > > One of the most common memory-to-memory device is the codec. Codecs > > > > are more complicated than most and require additional setup for > > > > their codec parameters. This is done through codec controls. > > > > -See :ref:`mpeg-controls`. > > > > +See :ref:`mpeg-controls`. More details on how to use codec memory-to-memory > > > > +devices are given in the following sections. > > > > + > > > > +.. toctree:: > > > > + :maxdepth: 1 > > > > + > > > > + dev-decoder > > > > diff --git a/Documentation/media/uapi/v4l/pixfmt-v4l2.rst b/Documentation/media/uapi/v4l/pixfmt-v4l2.rst > > > > index 71eebfc6d853..caf14e440447 100644 > > > > --- a/Documentation/media/uapi/v4l/pixfmt-v4l2.rst > > > > +++ b/Documentation/media/uapi/v4l/pixfmt-v4l2.rst > > > > @@ -39,6 +39,11 @@ Single-planar format structure > > > > to a multiple of the scale factor of any smaller planes. For > > > > example when the image format is YUV 4:2:0, ``width`` and > > > > ``height`` must be multiples of two. > > > > + > > > > + For compressed formats that contain the resolution information encoded > > > > + inside the stream, when fed to a stateful mem2mem decoder, the fields > > > > + may be zero to rely on the decoder to detect the right values. For more > > > > + details see :ref:`decoder` and format descriptions. > > > > * - __u32 > > > > - ``pixelformat`` > > > > - The pixel format or type of compression, set by the application. > > > > diff --git a/Documentation/media/uapi/v4l/v4l2.rst b/Documentation/media/uapi/v4l/v4l2.rst > > > > index 004ec00db6bd..97015b9b40b8 100644 > > > > --- a/Documentation/media/uapi/v4l/v4l2.rst > > > > +++ b/Documentation/media/uapi/v4l/v4l2.rst > > > > @@ -60,6 +60,10 @@ Authors, in alphabetical order: > > > > > > > > - Original author of the V4L2 API and documentation. > > > > > > > > +- Figa, Tomasz <tfiga@xxxxxxxxxxxx> > > > > + > > > > + - Documented the memory-to-memory decoder interface. > > > > + > > > > - H Schimek, Michael <mschimek@xxxxxx> > > > > > > > > - Original author of the V4L2 API and documentation. > > > > @@ -68,6 +72,10 @@ Authors, in alphabetical order: > > > > > > > > - Documented the Digital Video timings API. > > > > > > > > +- Osciak, Pawel <posciak@xxxxxxxxxxxx> > > > > + > > > > + - Documented the memory-to-memory decoder interface. > > > > + > > > > - Osciak, Pawel <pawel@xxxxxxxxxx> > > > > > > > > - Designed and documented the multi-planar API. > > > > @@ -92,7 +100,7 @@ Authors, in alphabetical order: > > > > > > > > - Designed and documented the VIDIOC_LOG_STATUS ioctl, the extended control ioctls, major parts of the sliced VBI API, the MPEG encoder and decoder APIs and the DV Timings API. > > > > > > > > -**Copyright** |copy| 1999-2016: Bill Dirks, Michael H. Schimek, Hans Verkuil, Martin Rubli, Andy Walls, Muralidharan Karicheri, Mauro Carvalho Chehab, Pawel Osciak, Sakari Ailus & Antti Palosaari. > > > > +**Copyright** |copy| 1999-2018: Bill Dirks, Michael H. Schimek, Hans Verkuil, Martin Rubli, Andy Walls, Muralidharan Karicheri, Mauro Carvalho Chehab, Pawel Osciak, Sakari Ailus & Antti Palosaari, Tomasz Figa > > > > > > > > Except when explicitly stated as GPL, programming examples within this > > > > part can be used and distributed without restrictions. > > > > diff --git a/Documentation/media/uapi/v4l/vidioc-decoder-cmd.rst b/Documentation/media/uapi/v4l/vidioc-decoder-cmd.rst > > > > index ccf83b05afa7..57f0066f4cff 100644 > > > > --- a/Documentation/media/uapi/v4l/vidioc-decoder-cmd.rst > > > > +++ b/Documentation/media/uapi/v4l/vidioc-decoder-cmd.rst > > > > @@ -56,14 +56,16 @@ The ``cmd`` field must contain the command code. Some commands use the > > > > > > > > A :ref:`write() <func-write>` or :ref:`VIDIOC_STREAMON` > > > > call sends an implicit START command to the decoder if it has not been > > > > -started yet. > > > > +started yet. Applies to both queues of mem2mem decoders. > > > > > > > > A :ref:`close() <func-close>` or :ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>` > > > > call of a streaming file descriptor sends an implicit immediate STOP > > > > -command to the decoder, and all buffered data is discarded. > > > > +command to the decoder, and all buffered data is discarded. Applies to both > > > > +queues of mem2mem decoders. > > > > > > > > -These ioctls are optional, not all drivers may support them. They were > > > > -introduced in Linux 3.3. > > > > +In principle, these ioctls are optional, not all drivers may support them. They were > > > > +introduced in Linux 3.3. They are, however, mandatory for stateful mem2mem decoders > > > > +(as further documented in :ref:`decoder`). > > > > > > > > > > > > .. tabularcolumns:: |p{1.1cm}|p{2.4cm}|p{1.2cm}|p{1.6cm}|p{10.6cm}| > > > > @@ -167,26 +169,32 @@ introduced in Linux 3.3. > > > > ``V4L2_DEC_CMD_RESUME`` for that. This command has one flag: > > > > ``V4L2_DEC_CMD_START_MUTE_AUDIO``. If set, then audio will be > > > > muted when playing back at a non-standard speed. > > > > + > > > > + For a device implementing the :ref:`decoder`, once the drain sequence > > > > + is initiated with the ``V4L2_DEC_CMD_STOP`` command, it must be driven > > > > + to completion before this command can be invoked. Any attempt to > > > > + invoke the command while the drain sequence is in progress will trigger > > > > + an ``EBUSY`` error code. The command may be also used to restart the > > > > + decoder in case of an implicit stop initiated by the decoder itself, > > > > + without the ``V4L2_DEC_CMD_STOP`` being called explicitly. See > > > > + :ref:`decoder` for more details. > > > > * - ``V4L2_DEC_CMD_STOP`` > > > > - 1 > > > > - Stop the decoder. When the decoder is already stopped, this > > > > command does nothing. This command has two flags: if > > > > ``V4L2_DEC_CMD_STOP_TO_BLACK`` is set, then the decoder will set > > > > the picture to black after it stopped decoding. Otherwise the last > > > > - image will repeat. mem2mem decoders will stop producing new frames > > > > - altogether. They will send a ``V4L2_EVENT_EOS`` event when the > > > > - last frame has been decoded and all frames are ready to be > > > > - dequeued and will set the ``V4L2_BUF_FLAG_LAST`` buffer flag on > > > > - the last buffer of the capture queue to indicate there will be no > > > > - new buffers produced to dequeue. This buffer may be empty, > > > > - indicated by the driver setting the ``bytesused`` field to 0. Once > > > > - the ``V4L2_BUF_FLAG_LAST`` flag was set, the > > > > - :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl will not block anymore, > > > > - but return an ``EPIPE`` error code. If > > > > + image will repeat. If > > > > ``V4L2_DEC_CMD_STOP_IMMEDIATELY`` is set, then the decoder stops > > > > immediately (ignoring the ``pts`` value), otherwise it will keep > > > > decoding until timestamp >= pts or until the last of the pending > > > > data from its internal buffers was decoded. > > > > + > > > > + For a device implementing the :ref:`decoder`, the command will initiate > > > > + the drain sequence as documented in :ref:`decoder`. No flags or other > > > > + arguments are accepted in this case. Any attempt to invoke the command > > > > + again before the sequence completes will trigger an ``EBUSY`` error > > > > + code. > > > > * - ``V4L2_DEC_CMD_PAUSE`` > > > > - 2 > > > > - Pause the decoder. When the decoder has not been started yet, the > > > > @@ -209,6 +217,11 @@ On success 0 is returned, on error -1 and the ``errno`` variable is set > > > > appropriately. The generic error codes are described at the > > > > :ref:`Generic Error Codes <gen-errors>` chapter. > > > > > > > > +EBUSY > > > > + A drain sequence of a device implementing the :ref:`decoder` is still in > > > > + progress. It is not allowed to issue another decoder command until it > > > > + completes. > > > > + > > > > EINVAL > > > > The ``cmd`` field is invalid. > > > >
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