linux-stable-rt/Documentation/DocBook/v4l/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, or there are no audio inputs at all and the ioctl is not
supported.</para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term><errorcode>EBUSY</errorcode></term>
	<listitem>
	  <para>I/O is in progress, the input cannot be
switched.</para>
	</listitem>
      </varlistentry>
    </variablelist>
  </refsect1>
</refentry>

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