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+.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
+.. c:namespace:: V4L
+
+.. _VIDIOC_DECODER_CMD:
+
+************************************************
+ioctl VIDIOC_DECODER_CMD, VIDIOC_TRY_DECODER_CMD
+************************************************
+
+Name
+====
+
+VIDIOC_DECODER_CMD - VIDIOC_TRY_DECODER_CMD - Execute an decoder command
+
+Synopsis
+========
+
+.. c:macro:: VIDIOC_DECODER_CMD
+
+``int ioctl(int fd, VIDIOC_DECODER_CMD, struct v4l2_decoder_cmd *argp)``
+
+.. c:macro:: VIDIOC_TRY_DECODER_CMD
+
+``int ioctl(int fd, VIDIOC_TRY_DECODER_CMD, struct v4l2_decoder_cmd *argp)``
+
+Arguments
+=========
+
+``fd``
+ File descriptor returned by :c:func:`open()`.
+
+``argp``
+ pointer to struct :c:type:`v4l2_decoder_cmd`.
+
+Description
+===========
+
+These ioctls control an audio/video (usually MPEG-) decoder.
+``VIDIOC_DECODER_CMD`` sends a command to the decoder,
+``VIDIOC_TRY_DECODER_CMD`` can be used to try a command without actually
+executing it. To send a command applications must initialize all fields
+of a struct :c:type:`v4l2_decoder_cmd` and call
+``VIDIOC_DECODER_CMD`` or ``VIDIOC_TRY_DECODER_CMD`` with a pointer to
+this structure.
+
+The ``cmd`` field must contain the command code. Some commands use the
+``flags`` field for additional information.
+
+A :c:func:`write()` or :ref:`VIDIOC_STREAMON`
+call sends an implicit START command to the decoder if it has not been
+started yet. Applies to both queues of mem2mem decoders.
+
+A :c: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. Applies to both
+queues of mem2mem decoders.
+
+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{2.0cm}|p{1.1cm}|p{2.2cm}|p{11.8cm}|
+
+.. c:type:: v4l2_decoder_cmd
+
+.. cssclass:: longtable
+
+.. flat-table:: struct v4l2_decoder_cmd
+ :header-rows: 0
+ :stub-columns: 0
+ :widths: 1 1 1 3
+
+ * - __u32
+ - ``cmd``
+ -
+ - The decoder command, see :ref:`decoder-cmds`.
+ * - __u32
+ - ``flags``
+ -
+ - Flags to go with the command. If no flags are defined for this
+ command, drivers and applications must set this field to zero.
+ * - union {
+ - (anonymous)
+ * - struct
+ - ``start``
+ -
+ - Structure containing additional data for the
+ ``V4L2_DEC_CMD_START`` command.
+ * -
+ - __s32
+ - ``speed``
+ - Playback speed and direction. The playback speed is defined as
+ ``speed``/1000 of the normal speed. So 1000 is normal playback.
+ Negative numbers denote reverse playback, so -1000 does reverse
+ playback at normal speed. Speeds -1, 0 and 1 have special
+ meanings: speed 0 is shorthand for 1000 (normal playback). A speed
+ of 1 steps just one frame forward, a speed of -1 steps just one
+ frame back.
+ * -
+ - __u32
+ - ``format``
+ - Format restrictions. This field is set by the driver, not the
+ application. Possible values are ``V4L2_DEC_START_FMT_NONE`` if
+ there are no format restrictions or ``V4L2_DEC_START_FMT_GOP`` if
+ the decoder operates on full GOPs (*Group Of Pictures*). This is
+ usually the case for reverse playback: the decoder needs full
+ GOPs, which it can then play in reverse order. So to implement
+ reverse playback the application must feed the decoder the last
+ GOP in the video file, then the GOP before that, etc. etc.
+ * - struct
+ - ``stop``
+ -
+ - Structure containing additional data for the ``V4L2_DEC_CMD_STOP``
+ command.
+ * -
+ - __u64
+ - ``pts``
+ - Stop playback at this ``pts`` or immediately if the playback is
+ already past that timestamp. Leave to 0 if you want to stop after
+ the last frame was decoded.
+ * - struct
+ - ``raw``
+ * -
+ - __u32
+ - ``data``\ [16]
+ - Reserved for future extensions. Drivers and applications must set
+ the array to zero.
+ * - }
+ -
+
+
+.. tabularcolumns:: |p{5.6cm}|p{0.6cm}|p{11.1cm}|
+
+.. cssclass:: longtable
+
+.. _decoder-cmds:
+
+.. flat-table:: Decoder Commands
+ :header-rows: 0
+ :stub-columns: 0
+ :widths: 56 6 113
+
+ * - ``V4L2_DEC_CMD_START``
+ - 0
+ - Start the decoder. When the decoder is already running or paused,
+ this command will just change the playback speed. That means that
+ calling ``V4L2_DEC_CMD_START`` when the decoder was paused will
+ *not* resume the decoder. You have to explicitly call
+ ``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. 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
+ driver will return an ``EPERM`` error code. When the decoder is
+ already paused, this command does nothing. This command has one
+ flag: if ``V4L2_DEC_CMD_PAUSE_TO_BLACK`` is set, then set the
+ decoder output to black when paused.
+ * - ``V4L2_DEC_CMD_RESUME``
+ - 3
+ - Resume decoding after a PAUSE command. When the decoder has not
+ been started yet, the driver will return an ``EPERM`` error code. When
+ the decoder is already running, this command does nothing. No
+ flags are defined for this command.
+ * - ``V4L2_DEC_CMD_FLUSH``
+ - 4
+ - Flush any held capture buffers. Only valid for stateless decoders.
+ This command is typically used when the application reached the
+ end of the stream and the last output buffer had the
+ ``V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF`` flag set. This would prevent
+ dequeueing the capture buffer containing the last decoded frame.
+ So this command can be used to explicitly flush that final decoded
+ frame. This command does nothing if there are no held capture buffers.
+
+Return Value
+============
+
+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.
+
+EPERM
+ The application sent a PAUSE or RESUME command when the decoder was
+ not running.