path: root/Documentation/DocBook/media/dvb/audio.xml

<title>DVB Audio Device</title>
<para>The DVB audio device controls the MPEG2 audio decoder of the DVB hardware. It
can be accessed through <emphasis role="tt">/dev/dvb/adapter0/audio0</emphasis>. Data types and and
ioctl definitions can be accessed by including <emphasis role="tt">linux/dvb/video.h</emphasis> in your
application.
</para>
<para>Please note that some DVB cards don&#8217;t have their own MPEG decoder, which results in
the omission of the audio and video device.
</para>

<section id="audio_data_types">
<title>Audio Data Types</title>
<para>This section describes the structures, data types and defines used when talking to the
audio device.
</para>

<section id="audio-stream-source-t">
<title>audio_stream_source_t</title>
<para>The audio stream source is set through the AUDIO_SELECT_SOURCE call and can take
the following values, depending on whether we are replaying from an internal (demux) or
external (user write) source.
</para>
<programlisting>
typedef enum {
	AUDIO_SOURCE_DEMUX,
	AUDIO_SOURCE_MEMORY
} audio_stream_source_t;
</programlisting>
<para>AUDIO_SOURCE_DEMUX selects the demultiplexer (fed either by the frontend or the
DVR device) as the source of the video stream. If AUDIO_SOURCE_MEMORY
is selected the stream comes from the application through the <emphasis role="tt">write()</emphasis> system
call.
</para>

</section>
<section id="audio-play-state-t">
<title>audio_play_state_t</title>
<para>The following values can be returned by the AUDIO_GET_STATUS call representing the
state of audio playback.
</para>
<programlisting>
typedef enum {
	AUDIO_STOPPED,
	AUDIO_PLAYING,
	AUDIO_PAUSED
} audio_play_state_t;
</programlisting>

</section>
<section id="audio-channel-select-t">
<title>audio_channel_select_t</title>
<para>The audio channel selected via AUDIO_CHANNEL_SELECT is determined by the
following values.
</para>
<programlisting>
typedef enum {
	AUDIO_STEREO,
	AUDIO_MONO_LEFT,
	AUDIO_MONO_RIGHT,
	AUDIO_MONO,
	AUDIO_STEREO_SWAPPED
} audio_channel_select_t;
</programlisting>

</section>
<section id="audio-status">
<title>struct audio_status</title>
<para>The AUDIO_GET_STATUS call returns the following structure informing about various
states of the playback operation.
</para>
<programlisting>
typedef struct audio_status {
	boolean AV_sync_state;
	boolean mute_state;
	audio_play_state_t play_state;
	audio_stream_source_t stream_source;
	audio_channel_select_t channel_select;
	boolean bypass_mode;
	audio_mixer_t mixer_state;
} audio_status_t;
</programlisting>

</section>
<section id="audio-mixer">
<title>struct audio_mixer</title>
<para>The following structure is used by the AUDIO_SET_MIXER call to set the audio
volume.
</para>
<programlisting>
typedef struct audio_mixer {
	unsigned int volume_left;
	unsigned int volume_right;
} audio_mixer_t;
</programlisting>

</section>
<section id="audio_encodings">
<title>audio encodings</title>
<para>A call to AUDIO_GET_CAPABILITIES returns an unsigned integer with the following
bits set according to the hardwares capabilities.
</para>
<programlisting>
 #define AUDIO_CAP_DTS    1
 #define AUDIO_CAP_LPCM   2
 #define AUDIO_CAP_MP1    4
 #define AUDIO_CAP_MP2    8
 #define AUDIO_CAP_MP3   16
 #define AUDIO_CAP_AAC   32
 #define AUDIO_CAP_OGG   64
 #define AUDIO_CAP_SDDS 128
 #define AUDIO_CAP_AC3  256
</programlisting>

</section>
<section id="audio-karaoke">
<title>struct audio_karaoke</title>
<para>The ioctl AUDIO_SET_KARAOKE uses the following format:
</para>
<programlisting>
typedef
struct audio_karaoke {
	int vocal1;
	int vocal2;
	int melody;
} audio_karaoke_t;
</programlisting>
<para>If Vocal1 or Vocal2 are non-zero, they get mixed into left and right t at 70% each. If both,
Vocal1 and Vocal2 are non-zero, Vocal1 gets mixed into the left channel and Vocal2 into the
right channel at 100% each. Ff Melody is non-zero, the melody channel gets mixed into left
and right.
</para>

</section>
<section id="audio-attributes-t">