Documentation/linux_tv/media/v4l/vidioc-encoder-cmd.rst

   1 .. -*- coding: utf-8; mode: rst -*-
   2
   3 .. _VIDIOC_ENCODER_CMD:
   4
   5 ************************************************
   6 ioctl VIDIOC_ENCODER_CMD, VIDIOC_TRY_ENCODER_CMD
   7 ************************************************
   8
   9 *man VIDIOC_ENCODER_CMD(2)*
  10
  11 VIDIOC_TRY_ENCODER_CMD
  12 Execute an encoder command
  13
  14
  15 Synopsis
  16 ========
  17
  18 .. cpp:function:: int ioctl( int fd, int request, struct v4l2_encoder_cmd *argp )
  19
  20 Arguments
  21 =========
  22
  23 ``fd``
  24     File descriptor returned by :ref:`open() <func-open>`.
  25
  26 ``request``
  27     VIDIOC_ENCODER_CMD, VIDIOC_TRY_ENCODER_CMD
  28
  29 ``argp``
  30
  31
  32 Description
  33 ===========
  34
  35 These ioctls control an audio/video (usually MPEG-) encoder.
  36 ``VIDIOC_ENCODER_CMD`` sends a command to the encoder,
  37 ``VIDIOC_TRY_ENCODER_CMD`` can be used to try a command without actually
  38 executing it.
  39
  40 To send a command applications must initialize all fields of a struct
  41 :ref:`v4l2_encoder_cmd <v4l2-encoder-cmd>` and call
  42 ``VIDIOC_ENCODER_CMD`` or ``VIDIOC_TRY_ENCODER_CMD`` with a pointer to
  43 this structure.
  44
  45 The ``cmd`` field must contain the command code. The ``flags`` field is
  46 currently only used by the STOP command and contains one bit: If the
  47 ``V4L2_ENC_CMD_STOP_AT_GOP_END`` flag is set, encoding will continue
  48 until the end of the current *Group Of Pictures*, otherwise it will stop
  49 immediately.
  50
  51 A :c:func:`read()`() or :ref:`VIDIOC_STREAMON`
  52 call sends an implicit START command to the encoder if it has not been
  53 started yet. After a STOP command, :c:func:`read()`() calls will read
  54 the remaining data buffered by the driver. When the buffer is empty,
  55 :c:func:`read()`() will return zero and the next :c:func:`read()`()
  56 call will restart the encoder.
  57
  58 A :c:func:`close()`() or :ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>`
  59 call of a streaming file descriptor sends an implicit immediate STOP to
  60 the encoder, and all buffered data is discarded.
  61
  62 These ioctls are optional, not all drivers may support them. They were
  63 introduced in Linux 2.6.21.
  64
  65
  66 .. _v4l2-encoder-cmd:
  67
  68 .. flat-table:: struct v4l2_encoder_cmd
  69     :header-rows:  0
  70     :stub-columns: 0
  71     :widths:       1 1 2
  72
  73
  74     -  .. row 1
  75
  76        -  __u32
  77
  78        -  ``cmd``
  79
  80        -  The encoder command, see :ref:`encoder-cmds`.
  81
  82     -  .. row 2
  83
  84        -  __u32
  85
  86        -  ``flags``
  87
  88        -  Flags to go with the command, see :ref:`encoder-flags`. If no
  89           flags are defined for this command, drivers and applications must
  90           set this field to zero.
  91
  92     -  .. row 3
  93
  94        -  __u32
  95
  96        -  ``data``\ [8]
  97
  98        -  Reserved for future extensions. Drivers and applications must set
  99           the array to zero.
 100
 101
 102
 103 .. _encoder-cmds:
 104
 105 .. flat-table:: Encoder Commands
 106     :header-rows:  0
 107     :stub-columns: 0
 108     :widths:       3 1 4
 109
 110
 111     -  .. row 1
 112
 113        -  ``V4L2_ENC_CMD_START``
 114
 115        -  0
 116
 117        -  Start the encoder. When the encoder is already running or paused,
 118           this command does nothing. No flags are defined for this command.
 119
 120     -  .. row 2
 121
 122        -  ``V4L2_ENC_CMD_STOP``
 123
 124        -  1
 125
 126        -  Stop the encoder. When the ``V4L2_ENC_CMD_STOP_AT_GOP_END`` flag
 127           is set, encoding will continue until the end of the current *Group
 128           Of Pictures*, otherwise encoding will stop immediately. When the
 129           encoder is already stopped, this command does nothing. mem2mem
 130           encoders will send a ``V4L2_EVENT_EOS`` event when the last frame
 131           has been encoded and all frames are ready to be dequeued and will
 132           set the ``V4L2_BUF_FLAG_LAST`` buffer flag on the last buffer of
 133           the capture queue to indicate there will be no new buffers
 134           produced to dequeue. This buffer may be empty, indicated by the
 135           driver setting the ``bytesused`` field to 0. Once the
 136           ``V4L2_BUF_FLAG_LAST`` flag was set, the
 137           :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl will not block anymore,
 138           but return an ``EPIPE`` error code.
 139
 140     -  .. row 3
 141
 142        -  ``V4L2_ENC_CMD_PAUSE``
 143
 144        -  2
 145
 146        -  Pause the encoder. When the encoder has not been started yet, the
 147           driver will return an ``EPERM`` error code. When the encoder is
 148           already paused, this command does nothing. No flags are defined
 149           for this command.
 150
 151     -  .. row 4
 152
 153        -  ``V4L2_ENC_CMD_RESUME``
 154
 155        -  3
 156
 157        -  Resume encoding after a PAUSE command. When the encoder has not
 158           been started yet, the driver will return an ``EPERM`` error code. When
 159           the encoder is already running, this command does nothing. No
 160           flags are defined for this command.
 161
 162
 163
 164 .. _encoder-flags:
 165
 166 .. flat-table:: Encoder Command Flags
 167     :header-rows:  0
 168     :stub-columns: 0
 169     :widths:       3 1 4
 170
 171
 172     -  .. row 1
 173
 174        -  ``V4L2_ENC_CMD_STOP_AT_GOP_END``
 175
 176        -  0x0001
 177
 178        -  Stop encoding at the end of the current *Group Of Pictures*,
 179           rather than immediately.
 180
 181
 182
 183 Return Value
 184 ============
 185
 186 On success 0 is returned, on error -1 and the ``errno`` variable is set
 187 appropriately. The generic error codes are described at the
 188 :ref:`Generic Error Codes <gen-errors>` chapter.
 189
 190 EINVAL
 191     The ``cmd`` field is invalid.
 192
 193 EPERM
 194     The application sent a PAUSE or RESUME command when the encoder was
 195     not running.
 196
 197
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