Documentation/linux_tv/media/v4l/vidioc-g-audio.rst

   1 .. -*- coding: utf-8; mode: rst -*-
   2
   3 .. _VIDIOC_G_AUDIO:
   4
   5 ************************************
   6 ioctl VIDIOC_G_AUDIO, VIDIOC_S_AUDIO
   7 ************************************
   8
   9 NAME
  10 ====
  11
  12 VIDIOC_G_AUDIO - VIDIOC_S_AUDIO - Query or select the current audio input and its attributes
  13
  14 SYNOPSIS
  15 ========
  16
  17 .. cpp:function:: int ioctl( int fd, int request, struct v4l2_audio *argp )
  18
  19 .. cpp:function:: int ioctl( int fd, int request, const struct v4l2_audio *argp )
  20
  21
  22 ARGUMENTS
  23 =========
  24
  25 ``fd``
  26     File descriptor returned by :ref:`open() <func-open>`.
  27
  28 ``request``
  29     VIDIOC_G_AUDIO, VIDIOC_S_AUDIO
  30
  31 ``argp``
  32
  33
  34 DESCRIPTION
  35 ===========
  36
  37 To query the current audio input applications zero out the ``reserved``
  38 array of a struct :ref:`v4l2_audio <v4l2-audio>` and call the
  39 :ref:`VIDIOC_G_AUDIO <VIDIOC_G_AUDIO>` ioctl with a pointer to this structure. Drivers fill
  40 the rest of the structure or return an ``EINVAL`` error code when the device
  41 has no audio inputs, or none which combine with the current video input.
  42
  43 Audio inputs have one writable property, the audio mode. To select the
  44 current audio input *and* change the audio mode, applications initialize
  45 the ``index`` and ``mode`` fields, and the ``reserved`` array of a
  46 :ref:`struct v4l2_audio <v4l2-audio>` structure and call the :ref:`VIDIOC_S_AUDIO <VIDIOC_G_AUDIO>`
  47 ioctl. Drivers may switch to a different audio mode if the request
  48 cannot be satisfied. However, this is a write-only ioctl, it does not
  49 return the actual new audio mode.
  50
  51
  52 .. _v4l2-audio:
  53
  54 .. flat-table:: struct v4l2_audio
  55     :header-rows:  0
  56     :stub-columns: 0
  57     :widths:       1 1 2
  58
  59
  60     -  .. row 1
  61
  62        -  __u32
  63
  64        -  ``index``
  65
  66        -  Identifies the audio input, set by the driver or application.
  67
  68     -  .. row 2
  69
  70        -  __u8
  71
  72        -  ``name``\ [32]
  73
  74        -  Name of the audio input, a NUL-terminated ASCII string, for
  75           example: "Line In". This information is intended for the user,
  76           preferably the connector label on the device itself.
  77
  78     -  .. row 3
  79
  80        -  __u32
  81
  82        -  ``capability``
  83
  84        -  Audio capability flags, see :ref:`audio-capability`.
  85
  86     -  .. row 4
  87
  88        -  __u32
  89
  90        -  ``mode``
  91
  92        -  Audio mode flags set by drivers and applications (on
  93           :ref:`VIDIOC_S_AUDIO <VIDIOC_G_AUDIO>` ioctl), see :ref:`audio-mode`.
  94
  95     -  .. row 5
  96
  97        -  __u32
  98
  99        -  ``reserved``\ [2]
 100
 101        -  Reserved for future extensions. Drivers and applications must set
 102           the array to zero.
 103
 104
 105
 106 .. _audio-capability:
 107
 108 .. flat-table:: Audio Capability Flags
 109     :header-rows:  0
 110     :stub-columns: 0
 111     :widths:       3 1 4
 112
 113
 114     -  .. row 1
 115
 116        -  ``V4L2_AUDCAP_STEREO``
 117
 118        -  0x00001
 119
 120        -  This is a stereo input. The flag is intended to automatically
 121           disable stereo recording etc. when the signal is always monaural.
 122           The API provides no means to detect if stereo is *received*,
 123           unless the audio input belongs to a tuner.
 124
 125     -  .. row 2
 126
 127        -  ``V4L2_AUDCAP_AVL``
 128
 129        -  0x00002
 130
 131        -  Automatic Volume Level mode is supported.
 132
 133
 134
 135 .. _audio-mode:
 136
 137 .. flat-table:: Audio Mode Flags
 138     :header-rows:  0
 139     :stub-columns: 0
 140     :widths:       3 1 4
 141
 142
 143     -  .. row 1
 144
 145        -  ``V4L2_AUDMODE_AVL``
 146
 147        -  0x00001
 148
 149        -  AVL mode is on.
 150
 151
 152 RETURN VALUE
 153 ============
 154
 155 On success 0 is returned, on error -1 and the ``errno`` variable is set
 156 appropriately. The generic error codes are described at the
 157 :ref:`Generic Error Codes <gen-errors>` chapter.
 158
 159 EINVAL
 160     No audio inputs combine with the current video input, or the number
 161     of the selected audio input is out of bounds or it does not combine.