1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2.. c:namespace:: V4L
3
4.. _VIDIOC_DECODER_CMD:
5
6************************************************
7ioctl VIDIOC_DECODER_CMD, VIDIOC_TRY_DECODER_CMD
8************************************************
9
10Name
11====
12
13VIDIOC_DECODER_CMD - VIDIOC_TRY_DECODER_CMD - Execute an decoder command
14
15Synopsis
16========
17
18.. c:macro:: VIDIOC_DECODER_CMD
19
20``int ioctl(int fd, VIDIOC_DECODER_CMD, struct v4l2_decoder_cmd *argp)``
21
22.. c:macro:: VIDIOC_TRY_DECODER_CMD
23
24``int ioctl(int fd, VIDIOC_TRY_DECODER_CMD, struct v4l2_decoder_cmd *argp)``
25
26Arguments
27=========
28
29``fd``
30    File descriptor returned by :c:func:`open()`.
31
32``argp``
33    pointer to struct :c:type:`v4l2_decoder_cmd`.
34
35Description
36===========
37
38These ioctls control an audio/video (usually MPEG-) decoder.
39``VIDIOC_DECODER_CMD`` sends a command to the decoder,
40``VIDIOC_TRY_DECODER_CMD`` can be used to try a command without actually
41executing it. To send a command applications must initialize all fields
42of a struct :c:type:`v4l2_decoder_cmd` and call
43``VIDIOC_DECODER_CMD`` or ``VIDIOC_TRY_DECODER_CMD`` with a pointer to
44this structure.
45
46The ``cmd`` field must contain the command code. Some commands use the
47``flags`` field for additional information.
48
49A :c:func:`write()` or :ref:`VIDIOC_STREAMON`
50call sends an implicit START command to the decoder if it has not been
51started yet. Applies to both queues of mem2mem decoders.
52
53A :c:func:`close()` or :ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>`
54call of a streaming file descriptor sends an implicit immediate STOP
55command to the decoder, and all buffered data is discarded. Applies to both
56queues of mem2mem decoders.
57
58In principle, these ioctls are optional, not all drivers may support them. They were
59introduced in Linux 3.3. They are, however, mandatory for stateful mem2mem decoders
60(as further documented in :ref:`decoder`).
61
62.. tabularcolumns:: |p{2.0cm}|p{1.1cm}|p{2.2cm}|p{11.8cm}|
63
64.. c:type:: v4l2_decoder_cmd
65
66.. cssclass:: longtable
67
68.. flat-table:: struct v4l2_decoder_cmd
69    :header-rows:  0
70    :stub-columns: 0
71    :widths: 1 1 1 3
72
73    * - __u32
74      - ``cmd``
75      -
76      - The decoder command, see :ref:`decoder-cmds`.
77    * - __u32
78      - ``flags``
79      -
80      - Flags to go with the command. If no flags are defined for this
81	command, drivers and applications must set this field to zero.
82    * - union {
83      - (anonymous)
84    * - struct
85      - ``start``
86      -
87      - Structure containing additional data for the
88	``V4L2_DEC_CMD_START`` command.
89    * -
90      - __s32
91      - ``speed``
92      - Playback speed and direction. The playback speed is defined as
93	``speed``/1000 of the normal speed. So 1000 is normal playback.
94	Negative numbers denote reverse playback, so -1000 does reverse
95	playback at normal speed. Speeds -1, 0 and 1 have special
96	meanings: speed 0 is shorthand for 1000 (normal playback). A speed
97	of 1 steps just one frame forward, a speed of -1 steps just one
98	frame back.
99    * -
100      - __u32
101      - ``format``
102      - Format restrictions. This field is set by the driver, not the
103	application. Possible values are ``V4L2_DEC_START_FMT_NONE`` if
104	there are no format restrictions or ``V4L2_DEC_START_FMT_GOP`` if
105	the decoder operates on full GOPs (*Group Of Pictures*). This is
106	usually the case for reverse playback: the decoder needs full
107	GOPs, which it can then play in reverse order. So to implement
108	reverse playback the application must feed the decoder the last
109	GOP in the video file, then the GOP before that, etc. etc.
110    * - struct
111      - ``stop``
112      -
113      - Structure containing additional data for the ``V4L2_DEC_CMD_STOP``
114	command.
115    * -
116      - __u64
117      - ``pts``
118      - Stop playback at this ``pts`` or immediately if the playback is
119	already past that timestamp. Leave to 0 if you want to stop after
120	the last frame was decoded.
121    * - struct
122      - ``raw``
123    * -
124      - __u32
125      - ``data``\ [16]
126      - Reserved for future extensions. Drivers and applications must set
127	the array to zero.
128    * - }
129      -
130
131
132.. tabularcolumns:: |p{5.6cm}|p{0.6cm}|p{11.1cm}|
133
134.. cssclass:: longtable
135
136.. _decoder-cmds:
137
138.. flat-table:: Decoder Commands
139    :header-rows:  0
140    :stub-columns: 0
141    :widths: 56 6 113
142
143    * - ``V4L2_DEC_CMD_START``
144      - 0
145      - Start the decoder. When the decoder is already running or paused,
146	this command will just change the playback speed. That means that
147	calling ``V4L2_DEC_CMD_START`` when the decoder was paused will
148	*not* resume the decoder. You have to explicitly call
149	``V4L2_DEC_CMD_RESUME`` for that. This command has one flag:
150	``V4L2_DEC_CMD_START_MUTE_AUDIO``. If set, then audio will be
151	muted when playing back at a non-standard speed.
152
153	For a device implementing the :ref:`decoder`, once the drain sequence
154	is initiated with the ``V4L2_DEC_CMD_STOP`` command, it must be driven
155	to completion before this command can be invoked.  Any attempt to
156	invoke the command while the drain sequence is in progress will trigger
157	an ``EBUSY`` error code.  The command may be also used to restart the
158	decoder in case of an implicit stop initiated by the decoder itself,
159	without the ``V4L2_DEC_CMD_STOP`` being called explicitly. See
160	:ref:`decoder` for more details.
161    * - ``V4L2_DEC_CMD_STOP``
162      - 1
163      - Stop the decoder. When the decoder is already stopped, this
164	command does nothing. This command has two flags: if
165	``V4L2_DEC_CMD_STOP_TO_BLACK`` is set, then the decoder will set
166	the picture to black after it stopped decoding. Otherwise the last
167	image will repeat. If
168	``V4L2_DEC_CMD_STOP_IMMEDIATELY`` is set, then the decoder stops
169	immediately (ignoring the ``pts`` value), otherwise it will keep
170	decoding until timestamp >= pts or until the last of the pending
171	data from its internal buffers was decoded.
172
173	For a device implementing the :ref:`decoder`, the command will initiate
174	the drain sequence as documented in :ref:`decoder`.  No flags or other
175	arguments are accepted in this case. Any attempt to invoke the command
176	again before the sequence completes will trigger an ``EBUSY`` error
177	code.
178    * - ``V4L2_DEC_CMD_PAUSE``
179      - 2
180      - Pause the decoder. When the decoder has not been started yet, the
181	driver will return an ``EPERM`` error code. When the decoder is
182	already paused, this command does nothing. This command has one
183	flag: if ``V4L2_DEC_CMD_PAUSE_TO_BLACK`` is set, then set the
184	decoder output to black when paused.
185    * - ``V4L2_DEC_CMD_RESUME``
186      - 3
187      - Resume decoding after a PAUSE command. When the decoder has not
188	been started yet, the driver will return an ``EPERM`` error code. When
189	the decoder is already running, this command does nothing. No
190	flags are defined for this command.
191    * - ``V4L2_DEC_CMD_FLUSH``
192      - 4
193      - Flush any held capture buffers. Only valid for stateless decoders.
194	This command is typically used when the application reached the
195	end of the stream and the last output buffer had the
196	``V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF`` flag set. This would prevent
197	dequeueing the capture buffer containing the last decoded frame.
198	So this command can be used to explicitly flush that final decoded
199	frame. This command does nothing if there are no held capture buffers.
200
201Return Value
202============
203
204On success 0 is returned, on error -1 and the ``errno`` variable is set
205appropriately. The generic error codes are described at the
206:ref:`Generic Error Codes <gen-errors>` chapter.
207
208EBUSY
209    A drain sequence of a device implementing the :ref:`decoder` is still in
210    progress. It is not allowed to issue another decoder command until it
211    completes.
212
213EINVAL
214    The ``cmd`` field is invalid.
215
216EPERM
217    The application sent a PAUSE or RESUME command when the decoder was
218    not running.
219