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6. vidioc-g-audio.xml

<refentry id="vidioc-g-audio">
  <refmeta>
    <refentrytitle>ioctl VIDIOC_G_AUDIO, VIDIOC_S_AUDIO</refentrytitle>
    &manvol;
  </refmeta>

  <refnamediv>
    <refname>VIDIOC_G_AUDIO</refname>
    <refname>VIDIOC_S_AUDIO</refname>
    <refpurpose>Query or select the current audio input and its
attributes</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <funcsynopsis>
      <funcprototype>
	<funcdef>int <function>ioctl</function></funcdef>
	<paramdef>int <parameter>fd</parameter></paramdef>
	<paramdef>int <parameter>request</parameter></paramdef>
	<paramdef>struct v4l2_audio *<parameter>argp</parameter></paramdef>
      </funcprototype>
    </funcsynopsis>
    <funcsynopsis>
      <funcprototype>
	<funcdef>int <function>ioctl</function></funcdef>
	<paramdef>int <parameter>fd</parameter></paramdef>
	<paramdef>int <parameter>request</parameter></paramdef>
	<paramdef>const struct v4l2_audio *<parameter>argp</parameter></paramdef>
      </funcprototype>
    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Arguments</title>

    <variablelist>
      <varlistentry>
	<term><parameter>fd</parameter></term>
	<listitem>
	  <para>&fd;</para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term><parameter>request</parameter></term>
	<listitem>
	  <para>VIDIOC_G_AUDIO, VIDIOC_S_AUDIO</para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term><parameter>argp</parameter></term>
	<listitem>
	  <para></para>
	</listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>Description</title>

    <para>To query the current audio input applications zero out the
<structfield>reserved</structfield> array of a &v4l2-audio;
and call the <constant>VIDIOC_G_AUDIO</constant> ioctl with a pointer
to this structure. Drivers fill the rest of the structure or return an
&EINVAL; when the device has no audio inputs, or none which combine
with the current video input.</para>

    <para>Audio inputs have one writable property, the audio mode. To
select the current audio input <emphasis>and</emphasis> change the
audio mode, applications initialize the
<structfield>index</structfield> and <structfield>mode</structfield>
fields, and the
<structfield>reserved</structfield> array of a
<structname>v4l2_audio</structname> structure and call the
<constant>VIDIOC_S_AUDIO</constant> ioctl. Drivers may switch to a
different audio mode if the request cannot be satisfied. However, this
is a write-only ioctl, it does not return the actual new audio
mode.</para>

    <table pgwide="1" frame="none" id="v4l2-audio">
      <title>struct <structname>v4l2_audio</structname></title>
      <tgroup cols="3">
	&cs-str;
	<tbody valign="top">
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>index</structfield></entry>
	    <entry>Identifies the audio input, set by the
driver or application.</entry>
	  </row>
	  <row>
	    <entry>__u8</entry>
	    <entry><structfield>name</structfield>[32]</entry>
	    <entry>Name of the audio input, a NUL-terminated ASCII
string, for example: "Line In". This information is intended for the
user, preferably the connector label on the device itself.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>capability</structfield></entry>
	    <entry>Audio capability flags, see <xref
		linkend="audio-capability" />.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>mode</structfield></entry>
	    <entry>Audio mode flags set by drivers and applications (on
	    <constant>VIDIOC_S_AUDIO</constant> ioctl), see <xref linkend="audio-mode" />.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>reserved</structfield>[2]</entry>
	    <entry>Reserved for future extensions. Drivers and
applications must set the array to zero.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>

    <table pgwide="1" frame="none" id="audio-capability">
      <title>Audio Capability Flags</title>
      <tgroup cols="3">
	&cs-def;
	<tbody valign="top">
	  <row>
	    <entry><constant>V4L2_AUDCAP_STEREO</constant></entry>
	    <entry>0x00001</entry>
	    <entry>This is a stereo input. The flag is intended to
automatically disable stereo recording etc. when the signal is always
monaural. The API provides no means to detect if stereo is
<emphasis>received</emphasis>, unless the audio input belongs to a
tuner.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_AUDCAP_AVL</constant></entry>
	    <entry>0x00002</entry>
	    <entry>Automatic Volume Level mode is supported.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>

    <table pgwide="1" frame="none" id="audio-mode">
      <title>Audio Mode Flags</title>
      <tgroup cols="3">
	&cs-def;
	<tbody valign="top">
	  <row>
	    <entry><constant>V4L2_AUDMODE_AVL</constant></entry>
	    <entry>0x00001</entry>
	    <entry>AVL mode is on.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>
  </refsect1>

  <refsect1>
    &return-value;

    <variablelist>
      <varlistentry>
	<term><errorcode>EINVAL</errorcode></term>
	<listitem>
	  <para>No audio inputs combine with the current video input,
or the number of the selected audio input is out of bounds or it does
not combine.</para>
	</listitem>
      </varlistentry>
    </variablelist>
  </refsect1>
</refentry>