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6. vidioc-g-audioout.xml

<refentry id="vidioc-g-audioout">
  <refmeta>
    <refentrytitle>ioctl VIDIOC_G_AUDOUT, VIDIOC_S_AUDOUT</refentrytitle>
    &manvol;
  </refmeta>

  <refnamediv>
    <refname>VIDIOC_G_AUDOUT</refname>
    <refname>VIDIOC_S_AUDOUT</refname>
    <refpurpose>Query or select the current audio output</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_audioout *<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_audioout *<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_AUDOUT, VIDIOC_S_AUDOUT</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 output applications zero out the
<structfield>reserved</structfield> array of a &v4l2-audioout; and
call the <constant>VIDIOC_G_AUDOUT</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 output.</para>

    <para>Audio outputs have no writable properties. Nevertheless, to
select the current audio output applications can initialize the
<structfield>index</structfield> field and
<structfield>reserved</structfield> array (which in the future may
contain writable properties) of a
<structname>v4l2_audioout</structname> structure and call the
<constant>VIDIOC_S_AUDOUT</constant> ioctl. Drivers switch to the
requested output or return the &EINVAL; when the index is out of
bounds. This is a write-only ioctl, it does not return the current
audio output attributes as <constant>VIDIOC_G_AUDOUT</constant>
does.</para>

    <para>Note connectors on a TV card to loop back the received audio
signal to a sound card are not audio outputs in this sense.</para>

    <table pgwide="1" frame="none" id="v4l2-audioout">
      <title>struct <structname>v4l2_audioout</structname></title>
      <tgroup cols="3">
	&cs-str;
	<tbody valign="top">
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>index</structfield></entry>
	    <entry>Identifies the audio output, set by the
driver or application.</entry>
	  </row>
	  <row>
	    <entry>__u8</entry>
	    <entry><structfield>name</structfield>[32]</entry>
	    <entry>Name of the audio output, a NUL-terminated ASCII
string, for example: "Line Out". 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, none defined yet. Drivers
must set this field to zero.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>mode</structfield></entry>
	    <entry>Audio mode, none defined yet. Drivers and
applications (on <constant>VIDIOC_S_AUDOUT</constant>) must set this
field to zero.</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>
  </refsect1>

  <refsect1>
    &return-value;

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