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Linux kernel mirror (for testing)
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linux
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.