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 .. c:function:: int ioctl( int fd, VIDIOC_DECODER_CMD, struct v4l2_decoder_cmd *argp )
  19     :name: VIDIOC_DECODER_CMD
  20
  21
  22 .. c:function:: int ioctl( int fd, VIDIOC_TRY_DECODER_CMD, struct v4l2_decoder_cmd *argp )
  23     :name: VIDIOC_TRY_DECODER_CMD
  24
  25
  26 Arguments
  27 =========
  28
  29 ``fd``
  30     File descriptor returned by :ref:`open() <func-open>`.
  31
  32 ``argp``
  33     pointer to struct :c:type:`v4l2_decoder_cmd`.
  34
  35
  36 Description
  37 ===========
  38
  39 These ioctls control an audio/video (usually MPEG-) decoder.
  40 ``VIDIOC_DECODER_CMD`` sends a command to the decoder,
  41 ``VIDIOC_TRY_DECODER_CMD`` can be used to try a command without actually
  42 executing it. To send a command applications must initialize all fields
  43 of a struct :c:type:`v4l2_decoder_cmd` and call
  44 ``VIDIOC_DECODER_CMD`` or ``VIDIOC_TRY_DECODER_CMD`` with a pointer to
  45 this structure.
  46
  47 The ``cmd`` field must contain the command code. Some commands use the
  48 ``flags`` field for additional information.
  49
  50 A :ref:`write() <func-write>` or :ref:`VIDIOC_STREAMON`
  51 call sends an implicit START command to the decoder if it has not been
  52 started yet.
  53
  54 A :ref:`close() <func-close>` or :ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>`
  55 call of a streaming file descriptor sends an implicit immediate STOP
  56 command to the decoder, and all buffered data is discarded.
  57
  58 These ioctls are optional, not all drivers may support them. They were
  59 introduced in Linux 3.3.
  60
  61
  62 .. tabularcolumns:: |p{1.1cm}|p{2.4cm}|p{1.2cm}|p{1.6cm}|p{10.6cm}|
  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: 11 24 12 16 106
  72
  73
  74     -  .. row 1
  75
  76        -  __u32
  77
  78        -  ``cmd``
  79
  80        -
  81        -
  82        -  The decoder command, see :ref:`decoder-cmds`.
  83
  84     -  .. row 2
  85
  86        -  __u32
  87
  88        -  ``flags``
  89
  90        -
  91        -
  92        -  Flags to go with the command. If no flags are defined for this
  93           command, drivers and applications must set this field to zero.
  94
  95     -  .. row 3
  96
  97        -  union
  98
  99        -  (anonymous)
 100
 101        -
 102        -
 103        -
 104
 105     -  .. row 4
 106
 107        -
 108        -  struct
 109
 110        -  ``start``
 111
 112        -
 113        -  Structure containing additional data for the
 114           ``V4L2_DEC_CMD_START`` command.
 115
 116     -  .. row 5
 117
 118        -
 119        -
 120        -  __s32
 121
 122        -  ``speed``
 123
 124        -  Playback speed and direction. The playback speed is defined as
 125           ``speed``/1000 of the normal speed. So 1000 is normal playback.
 126           Negative numbers denote reverse playback, so -1000 does reverse
 127           playback at normal speed. Speeds -1, 0 and 1 have special
 128           meanings: speed 0 is shorthand for 1000 (normal playback). A speed
 129           of 1 steps just one frame forward, a speed of -1 steps just one
 130           frame back.
 131
 132     -  .. row 6
 133
 134        -
 135        -
 136        -  __u32
 137
 138        -  ``format``
 139
 140        -  Format restrictions. This field is set by the driver, not the
 141           application. Possible values are ``V4L2_DEC_START_FMT_NONE`` if
 142           there are no format restrictions or ``V4L2_DEC_START_FMT_GOP`` if
 143           the decoder operates on full GOPs (*Group Of Pictures*). This is
 144           usually the case for reverse playback: the decoder needs full
 145           GOPs, which it can then play in reverse order. So to implement
 146           reverse playback the application must feed the decoder the last
 147           GOP in the video file, then the GOP before that, etc. etc.
 148
 149     -  .. row 7
 150
 151        -
 152        -  struct
 153
 154        -  ``stop``
 155
 156        -
 157        -  Structure containing additional data for the ``V4L2_DEC_CMD_STOP``
 158           command.
 159
 160     -  .. row 8
 161
 162        -
 163        -
 164        -  __u64
 165
 166        -  ``pts``
 167
 168        -  Stop playback at this ``pts`` or immediately if the playback is
 169           already past that timestamp. Leave to 0 if you want to stop after
 170           the last frame was decoded.
 171
 172     -  .. row 9
 173
 174        -
 175        -  struct
 176
 177        -  ``raw``
 178
 179        -
 180        -
 181
 182     -  .. row 10
 183
 184        -
 185        -
 186        -  __u32
 187
 188        -  ``data``\ [16]
 189
 190        -  Reserved for future extensions. Drivers and applications must set
 191           the array to zero.
 192
 193
 194
 195 .. tabularcolumns:: |p{5.6cm}|p{0.6cm}|p{11.3cm}|
 196
 197 .. _decoder-cmds:
 198
 199 .. flat-table:: Decoder Commands
 200     :header-rows:  0
 201     :stub-columns: 0
 202     :widths: 56 6 113
 203
 204
 205     -  .. row 1
 206
 207        -  ``V4L2_DEC_CMD_START``
 208
 209        -  0
 210
 211        -  Start the decoder. When the decoder is already running or paused,
 212           this command will just change the playback speed. That means that
 213           calling ``V4L2_DEC_CMD_START`` when the decoder was paused will
 214           *not* resume the decoder. You have to explicitly call
 215           ``V4L2_DEC_CMD_RESUME`` for that. This command has one flag:
 216           ``V4L2_DEC_CMD_START_MUTE_AUDIO``. If set, then audio will be
 217           muted when playing back at a non-standard speed.
 218
 219     -  .. row 2
 220
 221        -  ``V4L2_DEC_CMD_STOP``
 222
 223        -  1
 224
 225        -  Stop the decoder. When the decoder is already stopped, this
 226           command does nothing. This command has two flags: if
 227           ``V4L2_DEC_CMD_STOP_TO_BLACK`` is set, then the decoder will set
 228           the picture to black after it stopped decoding. Otherwise the last
 229           image will repeat. mem2mem decoders will stop producing new frames
 230           altogether. They will send a ``V4L2_EVENT_EOS`` event when the
 231           last frame has been decoded and all frames are ready to be
 232           dequeued and will set the ``V4L2_BUF_FLAG_LAST`` buffer flag on
 233           the last buffer of the capture queue to indicate there will be no
 234           new buffers produced to dequeue. This buffer may be empty,
 235           indicated by the driver setting the ``bytesused`` field to 0. Once
 236           the ``V4L2_BUF_FLAG_LAST`` flag was set, the
 237           :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl will not block anymore,
 238           but return an ``EPIPE`` error code. If
 239           ``V4L2_DEC_CMD_STOP_IMMEDIATELY`` is set, then the decoder stops
 240           immediately (ignoring the ``pts`` value), otherwise it will keep
 241           decoding until timestamp >= pts or until the last of the pending
 242           data from its internal buffers was decoded.
 243
 244     -  .. row 3
 245
 246        -  ``V4L2_DEC_CMD_PAUSE``
 247
 248        -  2
 249
 250        -  Pause the decoder. When the decoder has not been started yet, the
 251           driver will return an ``EPERM`` error code. When the decoder is
 252           already paused, this command does nothing. This command has one
 253           flag: if ``V4L2_DEC_CMD_PAUSE_TO_BLACK`` is set, then set the
 254           decoder output to black when paused.
 255
 256     -  .. row 4
 257
 258        -  ``V4L2_DEC_CMD_RESUME``
 259
 260        -  3
 261
 262        -  Resume decoding after a PAUSE command. When the decoder has not
 263           been started yet, the driver will return an ``EPERM`` error code. When
 264           the decoder is already running, this command does nothing. No
 265           flags are defined for this command.
 266
 267
 268 Return Value
 269 ============
 270
 271 On success 0 is returned, on error -1 and the ``errno`` variable is set
 272 appropriately. The generic error codes are described at the
 273 :ref:`Generic Error Codes <gen-errors>` chapter.
 274
 275 EINVAL
 276     The ``cmd`` field is invalid.
 277
 278 EPERM
 279     The application sent a PAUSE or RESUME command when the decoder was
 280     not running.