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 .. flat-table:: struct v4l2_decoder_cmd
  62     :header-rows:  0
  63     :stub-columns: 0
  64     :widths:       1 1 2 1 1
  65
  66
  67     -  .. row 1
  68
  69        -  __u32
  70
  71        -  ``cmd``
  72
  73        -
  74        -
  75        -  The decoder command, see :ref:`decoder-cmds`.
  76
  77     -  .. row 2
  78
  79        -  __u32
  80
  81        -  ``flags``
  82
  83        -
  84        -
  85        -  Flags to go with the command. If no flags are defined for this
  86           command, drivers and applications must set this field to zero.
  87
  88     -  .. row 3
  89
  90        -  union
  91
  92        -  (anonymous)
  93
  94        -
  95        -
  96        -
  97
  98     -  .. row 4
  99
 100        -
 101        -  struct
 102
 103        -  ``start``
 104
 105        -
 106        -  Structure containing additional data for the
 107           ``V4L2_DEC_CMD_START`` command.
 108
 109     -  .. row 5
 110
 111        -
 112        -
 113        -  __s32
 114
 115        -  ``speed``
 116
 117        -  Playback speed and direction. The playback speed is defined as
 118           ``speed``/1000 of the normal speed. So 1000 is normal playback.
 119           Negative numbers denote reverse playback, so -1000 does reverse
 120           playback at normal speed. Speeds -1, 0 and 1 have special
 121           meanings: speed 0 is shorthand for 1000 (normal playback). A speed
 122           of 1 steps just one frame forward, a speed of -1 steps just one
 123           frame back.
 124
 125     -  .. row 6
 126
 127        -
 128        -
 129        -  __u32
 130
 131        -  ``format``
 132
 133        -  Format restrictions. This field is set by the driver, not the
 134           application. Possible values are ``V4L2_DEC_START_FMT_NONE`` if
 135           there are no format restrictions or ``V4L2_DEC_START_FMT_GOP`` if
 136           the decoder operates on full GOPs (*Group Of Pictures*). This is
 137           usually the case for reverse playback: the decoder needs full
 138           GOPs, which it can then play in reverse order. So to implement
 139           reverse playback the application must feed the decoder the last
 140           GOP in the video file, then the GOP before that, etc. etc.
 141
 142     -  .. row 7
 143
 144        -
 145        -  struct
 146
 147        -  ``stop``
 148
 149        -
 150        -  Structure containing additional data for the ``V4L2_DEC_CMD_STOP``
 151           command.
 152
 153     -  .. row 8
 154
 155        -
 156        -
 157        -  __u64
 158
 159        -  ``pts``
 160
 161        -  Stop playback at this ``pts`` or immediately if the playback is
 162           already past that timestamp. Leave to 0 if you want to stop after
 163           the last frame was decoded.
 164
 165     -  .. row 9
 166
 167        -
 168        -  struct
 169
 170        -  ``raw``
 171
 172        -
 173        -
 174
 175     -  .. row 10
 176
 177        -
 178        -
 179        -  __u32
 180
 181        -  ``data``\ [16]
 182
 183        -  Reserved for future extensions. Drivers and applications must set
 184           the array to zero.
 185
 186
 187
 188 .. _decoder-cmds:
 189
 190 .. flat-table:: Decoder Commands
 191     :header-rows:  0
 192     :stub-columns: 0
 193     :widths:       3 1 4
 194
 195
 196     -  .. row 1
 197
 198        -  ``V4L2_DEC_CMD_START``
 199
 200        -  0
 201
 202        -  Start the decoder. When the decoder is already running or paused,
 203           this command will just change the playback speed. That means that
 204           calling ``V4L2_DEC_CMD_START`` when the decoder was paused will
 205           *not* resume the decoder. You have to explicitly call
 206           ``V4L2_DEC_CMD_RESUME`` for that. This command has one flag:
 207           ``V4L2_DEC_CMD_START_MUTE_AUDIO``. If set, then audio will be
 208           muted when playing back at a non-standard speed.
 209
 210     -  .. row 2
 211
 212        -  ``V4L2_DEC_CMD_STOP``
 213
 214        -  1
 215
 216        -  Stop the decoder. When the decoder is already stopped, this
 217           command does nothing. This command has two flags: if
 218           ``V4L2_DEC_CMD_STOP_TO_BLACK`` is set, then the decoder will set
 219           the picture to black after it stopped decoding. Otherwise the last
 220           image will repeat. mem2mem decoders will stop producing new frames
 221           altogether. They will send a ``V4L2_EVENT_EOS`` event when the
 222           last frame has been decoded and all frames are ready to be
 223           dequeued and will set the ``V4L2_BUF_FLAG_LAST`` buffer flag on
 224           the last buffer of the capture queue to indicate there will be no
 225           new buffers produced to dequeue. This buffer may be empty,
 226           indicated by the driver setting the ``bytesused`` field to 0. Once
 227           the ``V4L2_BUF_FLAG_LAST`` flag was set, the
 228           :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl will not block anymore,
 229           but return an ``EPIPE`` error code. If
 230           ``V4L2_DEC_CMD_STOP_IMMEDIATELY`` is set, then the decoder stops
 231           immediately (ignoring the ``pts`` value), otherwise it will keep
 232           decoding until timestamp >= pts or until the last of the pending
 233           data from its internal buffers was decoded.
 234
 235     -  .. row 3
 236
 237        -  ``V4L2_DEC_CMD_PAUSE``
 238
 239        -  2
 240
 241        -  Pause the decoder. When the decoder has not been started yet, the
 242           driver will return an ``EPERM`` error code. When the decoder is
 243           already paused, this command does nothing. This command has one
 244           flag: if ``V4L2_DEC_CMD_PAUSE_TO_BLACK`` is set, then set the
 245           decoder output to black when paused.
 246
 247     -  .. row 4
 248
 249        -  ``V4L2_DEC_CMD_RESUME``
 250
 251        -  3
 252
 253        -  Resume decoding after a PAUSE command. When the decoder has not
 254           been started yet, the driver will return an ``EPERM`` error code. When
 255           the decoder is already running, this command does nothing. No
 256           flags are defined for this command.
 257
 258
 259 Return Value
 260 ============
 261
 262 On success 0 is returned, on error -1 and the ``errno`` variable is set
 263 appropriately. The generic error codes are described at the
 264 :ref:`Generic Error Codes <gen-errors>` chapter.
 265
 266 EINVAL
 267     The ``cmd`` field is invalid.
 268
 269 EPERM
 270     The application sent a PAUSE or RESUME command when the decoder was
 271     not running.