Documentation/DocBook/media/v4l/vidioc-g-audio.xml

   1 <refentry id="vidioc-g-audio">
   2   <refmeta>
   3     <refentrytitle>ioctl VIDIOC_G_AUDIO, VIDIOC_S_AUDIO</refentrytitle>
   4     &manvol;
   5   </refmeta>
   6
   7   <refnamediv>
   8     <refname>VIDIOC_G_AUDIO</refname>
   9     <refname>VIDIOC_S_AUDIO</refname>
  10     <refpurpose>Query or select the current audio input and its
  11 attributes</refpurpose>
  12   </refnamediv>
  13
  14   <refsynopsisdiv>
  15     <funcsynopsis>
  16       <funcprototype>
  17         <funcdef>int <function>ioctl</function></funcdef>
  18         <paramdef>int <parameter>fd</parameter></paramdef>
  19         <paramdef>int <parameter>request</parameter></paramdef>
  20         <paramdef>struct v4l2_audio *<parameter>argp</parameter></paramdef>
  21       </funcprototype>
  22     </funcsynopsis>
  23     <funcsynopsis>
  24       <funcprototype>
  25         <funcdef>int <function>ioctl</function></funcdef>
  26         <paramdef>int <parameter>fd</parameter></paramdef>
  27         <paramdef>int <parameter>request</parameter></paramdef>
  28         <paramdef>const struct v4l2_audio *<parameter>argp</parameter></paramdef>
  29       </funcprototype>
  30     </funcsynopsis>
  31   </refsynopsisdiv>
  32
  33   <refsect1>
  34     <title>Arguments</title>
  35
  36     <variablelist>
  37       <varlistentry>
  38         <term><parameter>fd</parameter></term>
  39         <listitem>
  40           <para>&fd;</para>
  41         </listitem>
  42       </varlistentry>
  43       <varlistentry>
  44         <term><parameter>request</parameter></term>
  45         <listitem>
  46           <para>VIDIOC_G_AUDIO, VIDIOC_S_AUDIO</para>
  47         </listitem>
  48       </varlistentry>
  49       <varlistentry>
  50         <term><parameter>argp</parameter></term>
  51         <listitem>
  52           <para></para>
  53         </listitem>
  54       </varlistentry>
  55     </variablelist>
  56   </refsect1>
  57
  58   <refsect1>
  59     <title>Description</title>
  60
  61     <para>To query the current audio input applications zero out the
  62 <structfield>reserved</structfield> array of a &v4l2-audio;
  63 and call the <constant>VIDIOC_G_AUDIO</constant> ioctl with a pointer
  64 to this structure. Drivers fill the rest of the structure or return an
  65 &EINVAL; when the device has no audio inputs, or none which combine
  66 with the current video input.</para>
  67
  68     <para>Audio inputs have one writable property, the audio mode. To
  69 select the current audio input <emphasis>and</emphasis> change the
  70 audio mode, applications initialize the
  71 <structfield>index</structfield> and <structfield>mode</structfield>
  72 fields, and the
  73 <structfield>reserved</structfield> array of a
  74 <structname>v4l2_audio</structname> structure and call the
  75 <constant>VIDIOC_S_AUDIO</constant> ioctl. Drivers may switch to a
  76 different audio mode if the request cannot be satisfied. However, this
  77 is a write-only ioctl, it does not return the actual new audio
  78 mode.</para>
  79
  80     <table pgwide="1" frame="none" id="v4l2-audio">
  81       <title>struct <structname>v4l2_audio</structname></title>
  82       <tgroup cols="3">
  83         &cs-str;
  84         <tbody valign="top">
  85           <row>
  86             <entry>__u32</entry>
  87             <entry><structfield>index</structfield></entry>
  88             <entry>Identifies the audio input, set by the
  89 driver or application.</entry>
  90           </row>
  91           <row>
  92             <entry>__u8</entry>
  93             <entry><structfield>name</structfield>[32]</entry>
  94             <entry>Name of the audio input, a NUL-terminated ASCII
  95 string, for example: "Line In". This information is intended for the
  96 user, preferably the connector label on the device itself.</entry>
  97           </row>
  98           <row>
  99             <entry>__u32</entry>
 100             <entry><structfield>capability</structfield></entry>
 101             <entry>Audio capability flags, see <xref
 102                 linkend="audio-capability" />.</entry>
 103           </row>
 104           <row>
 105             <entry>__u32</entry>
 106             <entry><structfield>mode</structfield></entry>
 107             <entry>Audio mode flags set by drivers and applications (on
 108             <constant>VIDIOC_S_AUDIO</constant> ioctl), see <xref linkend="audio-mode" />.</entry>
 109           </row>
 110           <row>
 111             <entry>__u32</entry>
 112             <entry><structfield>reserved</structfield>[2]</entry>
 113             <entry>Reserved for future extensions. Drivers and
 114 applications must set the array to zero.</entry>
 115           </row>
 116         </tbody>
 117       </tgroup>
 118     </table>
 119
 120     <table pgwide="1" frame="none" id="audio-capability">
 121       <title>Audio Capability Flags</title>
 122       <tgroup cols="3">
 123         &cs-def;
 124         <tbody valign="top">
 125           <row>
 126             <entry><constant>V4L2_AUDCAP_STEREO</constant></entry>
 127             <entry>0x00001</entry>
 128             <entry>This is a stereo input. The flag is intended to
 129 automatically disable stereo recording etc. when the signal is always
 130 monaural. The API provides no means to detect if stereo is
 131 <emphasis>received</emphasis>, unless the audio input belongs to a
 132 tuner.</entry>
 133           </row>
 134           <row>
 135             <entry><constant>V4L2_AUDCAP_AVL</constant></entry>
 136             <entry>0x00002</entry>
 137             <entry>Automatic Volume Level mode is supported.</entry>
 138           </row>
 139         </tbody>
 140       </tgroup>
 141     </table>
 142
 143     <table pgwide="1" frame="none" id="audio-mode">
 144       <title>Audio Mode Flags</title>
 145       <tgroup cols="3">
 146         &cs-def;
 147         <tbody valign="top">
 148           <row>
 149             <entry><constant>V4L2_AUDMODE_AVL</constant></entry>
 150             <entry>0x00001</entry>
 151             <entry>AVL mode is on.</entry>
 152           </row>
 153         </tbody>
 154       </tgroup>
 155     </table>
 156   </refsect1>
 157
 158   <refsect1>
 159     &return-value;
 160
 161     <variablelist>
 162       <varlistentry>
 163         <term><errorcode>EINVAL</errorcode></term>
 164         <listitem>
 165           <para>No audio inputs combine with the current video input,
 166 or the number of the selected audio input is out of bounds or it does
 167 not combine.</para>
 168         </listitem>
 169       </varlistentry>
 170     </variablelist>
 171   </refsect1>
 172 </refentry>