Documentation/media/uapi/v4l/vidioc-decoder-cmd.rst

   1 .. -*- coding: utf-8; mode: rst -*-
   2
   3 .. _VIDIOC_DECODER_CMD:
   4
   5 ************************************************
   6 ioctl VIDIOC_DECODER_CMD, VIDIOC_TRY_DECODER_CMD
   7 ************************************************
   8
   9 Name
  10 ====
  11
  12 VIDIOC_DECODER_CMD - VIDIOC_TRY_DECODER_CMD - Execute an decoder command
  13
  14
  15 Synopsis
  16 ========
  17
  18 .. cpp:function:: int ioctl( int fd, int request, struct v4l2_decoder_cmd *argp )
  19
  20
  21 Arguments
  22 =========
  23
  24 ``fd``
  25     File descriptor returned by :ref:`open() <func-open>`.
  26
  27 ``request``
  28     VIDIOC_DECODER_CMD, VIDIOC_TRY_DECODER_CMD
  29
  30 ``argp``
  31
  32
  33 Description
  34 ===========
  35
  36 These ioctls control an audio/video (usually MPEG-) decoder.
  37 ``VIDIOC_DECODER_CMD`` sends a command to the decoder,
  38 ``VIDIOC_TRY_DECODER_CMD`` can be used to try a command without actually
  39 executing it. To send a command applications must initialize all fields
  40 of a struct :ref:`v4l2_decoder_cmd <v4l2-decoder-cmd>` and call
  41 ``VIDIOC_DECODER_CMD`` or ``VIDIOC_TRY_DECODER_CMD`` with a pointer to
  42 this structure.
  43
  44 The ``cmd`` field must contain the command code. Some commands use the
  45 ``flags`` field for additional information.
  46
  47 A :ref:`write() <func-write>` or :ref:`VIDIOC_STREAMON`
  48 call sends an implicit START command to the decoder if it has not been
  49 started yet.
  50
  51 A :ref:`close() <func-close>` or :ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>`
  52 call of a streaming file descriptor sends an implicit immediate STOP
  53 command to the decoder, and all buffered data is discarded.
  54
  55 These ioctls are optional, not all drivers may support them. They were
  56 introduced in Linux 3.3.
  57
  58
  59 .. _v4l2-decoder-cmd:
  60
  61 .. tabularcolumns:: |p{2.9cm}|p{2.9cm}|p{5.8cm}|p{2.9cm}|p{3.0cm}|
  62
  63 .. flat-table:: struct v4l2_decoder_cmd
  64     :header-rows:  0
  65     :stub-columns: 0
  66     :widths:       1 1 2 1 1
  67
  68
  69     -  .. row 1
  70
  71        -  __u32
  72
  73        -  ``cmd``
  74
  75        -
  76        -
  77        -  The decoder command, see :ref:`decoder-cmds`.
  78
  79     -  .. row 2
  80
  81        -  __u32
  82
  83        -  ``flags``
  84
  85        -
  86        -
  87        -  Flags to go with the command. If no flags are defined for this
  88           command, drivers and applications must set this field to zero.
  89
  90     -  .. row 3
  91
  92        -  union
  93
  94        -  (anonymous)
  95
  96        -
  97        -
  98        -
  99
 100     -  .. row 4
 101
 102        -
 103        -  struct
 104
 105        -  ``start``
 106
 107        -
 108        -  Structure containing additional data for the
 109           ``V4L2_DEC_CMD_START`` command.
 110
 111     -  .. row 5
 112
 113        -
 114        -
 115        -  __s32
 116
 117        -  ``speed``
 118
 119        -  Playback speed and direction. The playback speed is defined as
 120           ``speed``/1000 of the normal speed. So 1000 is normal playback.
 121           Negative numbers denote reverse playback, so -1000 does reverse
 122           playback at normal speed. Speeds -1, 0 and 1 have special
 123           meanings: speed 0 is shorthand for 1000 (normal playback). A speed
 124           of 1 steps just one frame forward, a speed of -1 steps just one
 125           frame back.
 126
 127     -  .. row 6
 128
 129        -
 130        -
 131        -  __u32
 132
 133        -  ``format``
 134
 135        -  Format restrictions. This field is set by the driver, not the
 136           application. Possible values are ``V4L2_DEC_START_FMT_NONE`` if
 137           there are no format restrictions or ``V4L2_DEC_START_FMT_GOP`` if
 138           the decoder operates on full GOPs (*Group Of Pictures*). This is
 139           usually the case for reverse playback: the decoder needs full
 140           GOPs, which it can then play in reverse order. So to implement
 141           reverse playback the application must feed the decoder the last
 142           GOP in the video file, then the GOP before that, etc. etc.
 143
 144     -  .. row 7
 145
 146        -
 147        -  struct
 148
 149        -  ``stop``
 150
 151        -
 152        -  Structure containing additional data for the ``V4L2_DEC_CMD_STOP``
 153           command.
 154
 155     -  .. row 8
 156
 157        -
 158        -
 159        -  __u64
 160
 161        -  ``pts``
 162
 163        -  Stop playback at this ``pts`` or immediately if the playback is
 164           already past that timestamp. Leave to 0 if you want to stop after
 165           the last frame was decoded.
 166
 167     -  .. row 9
 168
 169        -
 170        -  struct
 171
 172        -  ``raw``
 173
 174        -
 175        -
 176
 177     -  .. row 10
 178
 179        -
 180        -
 181        -  __u32
 182
 183        -  ``data``\ [16]
 184
 185        -  Reserved for future extensions. Drivers and applications must set
 186           the array to zero.
 187
 188
 189
 190 .. _decoder-cmds:
 191
 192 .. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|
 193
 194 .. flat-table:: Decoder Commands
 195     :header-rows:  0
 196     :stub-columns: 0
 197     :widths:       3 1 4
 198
 199
 200     -  .. row 1
 201
 202        -  ``V4L2_DEC_CMD_START``
 203
 204        -  0
 205
 206        -  Start the decoder. When the decoder is already running or paused,
 207           this command will just change the playback speed. That means that
 208           calling ``V4L2_DEC_CMD_START`` when the decoder was paused will
 209           *not* resume the decoder. You have to explicitly call
 210           ``V4L2_DEC_CMD_RESUME`` for that. This command has one flag:
 211           ``V4L2_DEC_CMD_START_MUTE_AUDIO``. If set, then audio will be
 212           muted when playing back at a non-standard speed.
 213
 214     -  .. row 2
 215
 216        -  ``V4L2_DEC_CMD_STOP``
 217
 218        -  1
 219
 220        -  Stop the decoder. When the decoder is already stopped, this
 221           command does nothing. This command has two flags: if
 222           ``V4L2_DEC_CMD_STOP_TO_BLACK`` is set, then the decoder will set
 223           the picture to black after it stopped decoding. Otherwise the last
 224           image will repeat. mem2mem decoders will stop producing new frames
 225           altogether. They will send a ``V4L2_EVENT_EOS`` event when the
 226           last frame has been decoded and all frames are ready to be
 227           dequeued and will set the ``V4L2_BUF_FLAG_LAST`` buffer flag on
 228           the last buffer of the capture queue to indicate there will be no
 229           new buffers produced to dequeue. This buffer may be empty,
 230           indicated by the driver setting the ``bytesused`` field to 0. Once
 231           the ``V4L2_BUF_FLAG_LAST`` flag was set, the
 232           :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl will not block anymore,
 233           but return an ``EPIPE`` error code. If
 234           ``V4L2_DEC_CMD_STOP_IMMEDIATELY`` is set, then the decoder stops
 235           immediately (ignoring the ``pts`` value), otherwise it will keep
 236           decoding until timestamp >= pts or until the last of the pending
 237           data from its internal buffers was decoded.
 238
 239     -  .. row 3
 240
 241        -  ``V4L2_DEC_CMD_PAUSE``
 242
 243        -  2
 244
 245        -  Pause the decoder. When the decoder has not been started yet, the
 246           driver will return an ``EPERM`` error code. When the decoder is
 247           already paused, this command does nothing. This command has one
 248           flag: if ``V4L2_DEC_CMD_PAUSE_TO_BLACK`` is set, then set the
 249           decoder output to black when paused.
 250
 251     -  .. row 4
 252
 253        -  ``V4L2_DEC_CMD_RESUME``
 254
 255        -  3
 256
 257        -  Resume decoding after a PAUSE command. When the decoder has not
 258           been started yet, the driver will return an ``EPERM`` error code. When
 259           the decoder is already running, this command does nothing. No
 260           flags are defined for this command.
 261
 262
 263 Return Value
 264 ============
 265
 266 On success 0 is returned, on error -1 and the ``errno`` variable is set
 267 appropriately. The generic error codes are described at the
 268 :ref:`Generic Error Codes <gen-errors>` chapter.
 269
 270 EINVAL
 271     The ``cmd`` field is invalid.
 272
 273 EPERM
 274     The application sent a PAUSE or RESUME command when the decoder was
 275     not running.