1.. Permission is granted to copy, distribute and/or modify this
2.. document under the terms of the GNU Free Documentation License,
3.. Version 1.1 or any later version published by the Free Software
4.. Foundation, with no Invariant Sections, no Front-Cover Texts
5.. and no Back-Cover Texts. A copy of the license is included at
6.. Documentation/userspace-api/media/fdl-appendix.rst.
7..
8.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections
9
10.. _VIDIOC_DECODER_CMD:
11
12************************************************
13ioctl VIDIOC_DECODER_CMD, VIDIOC_TRY_DECODER_CMD
14************************************************
15
16Name
17====
18
19VIDIOC_DECODER_CMD - VIDIOC_TRY_DECODER_CMD - Execute an decoder command
20
21
22Synopsis
23========
24
25.. c:function:: int ioctl( int fd, VIDIOC_DECODER_CMD, struct v4l2_decoder_cmd *argp )
26    :name: VIDIOC_DECODER_CMD
27
28
29.. c:function:: int ioctl( int fd, VIDIOC_TRY_DECODER_CMD, struct v4l2_decoder_cmd *argp )
30    :name: VIDIOC_TRY_DECODER_CMD
31
32
33Arguments
34=========
35
36``fd``
37    File descriptor returned by :ref:`open() <func-open>`.
38
39``argp``
40    pointer to struct :c:type:`v4l2_decoder_cmd`.
41
42
43Description
44===========
45
46These ioctls control an audio/video (usually MPEG-) decoder.
47``VIDIOC_DECODER_CMD`` sends a command to the decoder,
48``VIDIOC_TRY_DECODER_CMD`` can be used to try a command without actually
49executing it. To send a command applications must initialize all fields
50of a struct :c:type:`v4l2_decoder_cmd` and call
51``VIDIOC_DECODER_CMD`` or ``VIDIOC_TRY_DECODER_CMD`` with a pointer to
52this structure.
53
54The ``cmd`` field must contain the command code. Some commands use the
55``flags`` field for additional information.
56
57A :ref:`write() <func-write>` or :ref:`VIDIOC_STREAMON`
58call sends an implicit START command to the decoder if it has not been
59started yet. Applies to both queues of mem2mem decoders.
60
61A :ref:`close() <func-close>` or :ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>`
62call of a streaming file descriptor sends an implicit immediate STOP
63command to the decoder, and all buffered data is discarded. Applies to both
64queues of mem2mem decoders.
65
66In principle, these ioctls are optional, not all drivers may support them. They were
67introduced in Linux 3.3. They are, however, mandatory for stateful mem2mem decoders
68(as further documented in :ref:`decoder`).
69
70
71.. tabularcolumns:: |p{1.1cm}|p{2.4cm}|p{1.2cm}|p{1.6cm}|p{10.6cm}|
72
73.. c:type:: v4l2_decoder_cmd
74
75.. cssclass:: longtable
76
77.. flat-table:: struct v4l2_decoder_cmd
78    :header-rows:  0
79    :stub-columns: 0
80    :widths: 1 1 1 3
81
82    * - __u32
83      - ``cmd``
84      -
85      - The decoder command, see :ref:`decoder-cmds`.
86    * - __u32
87      - ``flags``
88      -
89      - Flags to go with the command. If no flags are defined for this
90	command, drivers and applications must set this field to zero.
91    * - union {
92      - (anonymous)
93    * - struct
94      - ``start``
95      -
96      - Structure containing additional data for the
97	``V4L2_DEC_CMD_START`` command.
98    * -
99      - __s32
100      - ``speed``
101      - Playback speed and direction. The playback speed is defined as
102	``speed``/1000 of the normal speed. So 1000 is normal playback.
103	Negative numbers denote reverse playback, so -1000 does reverse
104	playback at normal speed. Speeds -1, 0 and 1 have special
105	meanings: speed 0 is shorthand for 1000 (normal playback). A speed
106	of 1 steps just one frame forward, a speed of -1 steps just one
107	frame back.
108    * -
109      - __u32
110      - ``format``
111      - Format restrictions. This field is set by the driver, not the
112	application. Possible values are ``V4L2_DEC_START_FMT_NONE`` if
113	there are no format restrictions or ``V4L2_DEC_START_FMT_GOP`` if
114	the decoder operates on full GOPs (*Group Of Pictures*). This is
115	usually the case for reverse playback: the decoder needs full
116	GOPs, which it can then play in reverse order. So to implement
117	reverse playback the application must feed the decoder the last
118	GOP in the video file, then the GOP before that, etc. etc.
119    * - struct
120      - ``stop``
121      -
122      - Structure containing additional data for the ``V4L2_DEC_CMD_STOP``
123	command.
124    * -
125      - __u64
126      - ``pts``
127      - Stop playback at this ``pts`` or immediately if the playback is
128	already past that timestamp. Leave to 0 if you want to stop after
129	the last frame was decoded.
130    * - struct
131      - ``raw``
132    * -
133      - __u32
134      - ``data``\ [16]
135      - Reserved for future extensions. Drivers and applications must set
136	the array to zero.
137    * - }
138      -
139
140
141
142.. tabularcolumns:: |p{5.6cm}|p{0.6cm}|p{11.3cm}|
143
144.. _decoder-cmds:
145
146.. flat-table:: Decoder Commands
147    :header-rows:  0
148    :stub-columns: 0
149    :widths: 56 6 113
150
151    * - ``V4L2_DEC_CMD_START``
152      - 0
153      - Start the decoder. When the decoder is already running or paused,
154	this command will just change the playback speed. That means that
155	calling ``V4L2_DEC_CMD_START`` when the decoder was paused will
156	*not* resume the decoder. You have to explicitly call
157	``V4L2_DEC_CMD_RESUME`` for that. This command has one flag:
158	``V4L2_DEC_CMD_START_MUTE_AUDIO``. If set, then audio will be
159	muted when playing back at a non-standard speed.
160
161	For a device implementing the :ref:`decoder`, once the drain sequence
162	is initiated with the ``V4L2_DEC_CMD_STOP`` command, it must be driven
163	to completion before this command can be invoked.  Any attempt to
164	invoke the command while the drain sequence is in progress will trigger
165	an ``EBUSY`` error code.  The command may be also used to restart the
166	decoder in case of an implicit stop initiated by the decoder itself,
167	without the ``V4L2_DEC_CMD_STOP`` being called explicitly. See
168	:ref:`decoder` for more details.
169    * - ``V4L2_DEC_CMD_STOP``
170      - 1
171      - Stop the decoder. When the decoder is already stopped, this
172	command does nothing. This command has two flags: if
173	``V4L2_DEC_CMD_STOP_TO_BLACK`` is set, then the decoder will set
174	the picture to black after it stopped decoding. Otherwise the last
175	image will repeat. If
176	``V4L2_DEC_CMD_STOP_IMMEDIATELY`` is set, then the decoder stops
177	immediately (ignoring the ``pts`` value), otherwise it will keep
178	decoding until timestamp >= pts or until the last of the pending
179	data from its internal buffers was decoded.
180
181	For a device implementing the :ref:`decoder`, the command will initiate
182	the drain sequence as documented in :ref:`decoder`.  No flags or other
183	arguments are accepted in this case. Any attempt to invoke the command
184	again before the sequence completes will trigger an ``EBUSY`` error
185	code.
186    * - ``V4L2_DEC_CMD_PAUSE``
187      - 2
188      - Pause the decoder. When the decoder has not been started yet, the
189	driver will return an ``EPERM`` error code. When the decoder is
190	already paused, this command does nothing. This command has one
191	flag: if ``V4L2_DEC_CMD_PAUSE_TO_BLACK`` is set, then set the
192	decoder output to black when paused.
193    * - ``V4L2_DEC_CMD_RESUME``
194      - 3
195      - Resume decoding after a PAUSE command. When the decoder has not
196	been started yet, the driver will return an ``EPERM`` error code. When
197	the decoder is already running, this command does nothing. No
198	flags are defined for this command.
199    * - ``V4L2_DEC_CMD_FLUSH``
200      - 4
201      - Flush any held capture buffers. Only valid for stateless decoders.
202	This command is typically used when the application reached the
203	end of the stream and the last output buffer had the
204	``V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF`` flag set. This would prevent
205	dequeueing the capture buffer containing the last decoded frame.
206	So this command can be used to explicitly flush that final decoded
207	frame. This command does nothing if there are no held capture buffers.
208
209Return Value
210============
211
212On success 0 is returned, on error -1 and the ``errno`` variable is set
213appropriately. The generic error codes are described at the
214:ref:`Generic Error Codes <gen-errors>` chapter.
215
216EBUSY
217    A drain sequence of a device implementing the :ref:`decoder` is still in
218    progress. It is not allowed to issue another decoder command until it
219    completes.
220
221EINVAL
222    The ``cmd`` field is invalid.
223
224EPERM
225    The application sent a PAUSE or RESUME command when the decoder was
226    not running.
227