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/media/uapi/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: 11 24 12 16 106 81 82 * - __u32 83 - ``cmd`` 84 - 85 - 86 - The decoder command, see :ref:`decoder-cmds`. 87 * - __u32 88 - ``flags`` 89 - 90 - 91 - Flags to go with the command. If no flags are defined for this 92 command, drivers and applications must set this field to zero. 93 * - union 94 - (anonymous) 95 - 96 - 97 - 98 * - 99 - struct 100 - ``start`` 101 - 102 - Structure containing additional data for the 103 ``V4L2_DEC_CMD_START`` command. 104 * - 105 - 106 - __s32 107 - ``speed`` 108 - Playback speed and direction. The playback speed is defined as 109 ``speed``/1000 of the normal speed. So 1000 is normal playback. 110 Negative numbers denote reverse playback, so -1000 does reverse 111 playback at normal speed. Speeds -1, 0 and 1 have special 112 meanings: speed 0 is shorthand for 1000 (normal playback). A speed 113 of 1 steps just one frame forward, a speed of -1 steps just one 114 frame back. 115 * - 116 - 117 - __u32 118 - ``format`` 119 - Format restrictions. This field is set by the driver, not the 120 application. Possible values are ``V4L2_DEC_START_FMT_NONE`` if 121 there are no format restrictions or ``V4L2_DEC_START_FMT_GOP`` if 122 the decoder operates on full GOPs (*Group Of Pictures*). This is 123 usually the case for reverse playback: the decoder needs full 124 GOPs, which it can then play in reverse order. So to implement 125 reverse playback the application must feed the decoder the last 126 GOP in the video file, then the GOP before that, etc. etc. 127 * - 128 - struct 129 - ``stop`` 130 - 131 - Structure containing additional data for the ``V4L2_DEC_CMD_STOP`` 132 command. 133 * - 134 - 135 - __u64 136 - ``pts`` 137 - Stop playback at this ``pts`` or immediately if the playback is 138 already past that timestamp. Leave to 0 if you want to stop after 139 the last frame was decoded. 140 * - 141 - struct 142 - ``raw`` 143 - 144 - 145 * - 146 - 147 - __u32 148 - ``data``\ [16] 149 - Reserved for future extensions. Drivers and applications must set 150 the array to zero. 151 152 153 154.. tabularcolumns:: |p{5.6cm}|p{0.6cm}|p{11.3cm}| 155 156.. _decoder-cmds: 157 158.. flat-table:: Decoder Commands 159 :header-rows: 0 160 :stub-columns: 0 161 :widths: 56 6 113 162 163 * - ``V4L2_DEC_CMD_START`` 164 - 0 165 - Start the decoder. When the decoder is already running or paused, 166 this command will just change the playback speed. That means that 167 calling ``V4L2_DEC_CMD_START`` when the decoder was paused will 168 *not* resume the decoder. You have to explicitly call 169 ``V4L2_DEC_CMD_RESUME`` for that. This command has one flag: 170 ``V4L2_DEC_CMD_START_MUTE_AUDIO``. If set, then audio will be 171 muted when playing back at a non-standard speed. 172 173 For a device implementing the :ref:`decoder`, once the drain sequence 174 is initiated with the ``V4L2_DEC_CMD_STOP`` command, it must be driven 175 to completion before this command can be invoked. Any attempt to 176 invoke the command while the drain sequence is in progress will trigger 177 an ``EBUSY`` error code. The command may be also used to restart the 178 decoder in case of an implicit stop initiated by the decoder itself, 179 without the ``V4L2_DEC_CMD_STOP`` being called explicitly. See 180 :ref:`decoder` for more details. 181 * - ``V4L2_DEC_CMD_STOP`` 182 - 1 183 - Stop the decoder. When the decoder is already stopped, this 184 command does nothing. This command has two flags: if 185 ``V4L2_DEC_CMD_STOP_TO_BLACK`` is set, then the decoder will set 186 the picture to black after it stopped decoding. Otherwise the last 187 image will repeat. If 188 ``V4L2_DEC_CMD_STOP_IMMEDIATELY`` is set, then the decoder stops 189 immediately (ignoring the ``pts`` value), otherwise it will keep 190 decoding until timestamp >= pts or until the last of the pending 191 data from its internal buffers was decoded. 192 193 For a device implementing the :ref:`decoder`, the command will initiate 194 the drain sequence as documented in :ref:`decoder`. No flags or other 195 arguments are accepted in this case. Any attempt to invoke the command 196 again before the sequence completes will trigger an ``EBUSY`` error 197 code. 198 * - ``V4L2_DEC_CMD_PAUSE`` 199 - 2 200 - Pause the decoder. When the decoder has not been started yet, the 201 driver will return an ``EPERM`` error code. When the decoder is 202 already paused, this command does nothing. This command has one 203 flag: if ``V4L2_DEC_CMD_PAUSE_TO_BLACK`` is set, then set the 204 decoder output to black when paused. 205 * - ``V4L2_DEC_CMD_RESUME`` 206 - 3 207 - Resume decoding after a PAUSE command. When the decoder has not 208 been started yet, the driver will return an ``EPERM`` error code. When 209 the decoder is already running, this command does nothing. No 210 flags are defined for this command. 211 212 213Return Value 214============ 215 216On success 0 is returned, on error -1 and the ``errno`` variable is set 217appropriately. The generic error codes are described at the 218:ref:`Generic Error Codes <gen-errors>` chapter. 219 220EBUSY 221 A drain sequence of a device implementing the :ref:`decoder` is still in 222 progress. It is not allowed to issue another decoder command until it 223 completes. 224 225EINVAL 226 The ``cmd`` field is invalid. 227 228EPERM 229 The application sent a PAUSE or RESUME command when the decoder was 230 not running. 231