vidioc-decoder-cmd.rst (7773B)
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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.