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<chapter> <title> The audio output layer </title>
<sect1> <title> Data exchanges between a decoder and the audio output
</title>
<para>
The audio output basically takes audio samples from one or several
FIFOs, mixes and resamples them, and plays them through the audio
chip. Data exchanges are simple and described in <filename>
src/audio_output/audio_output.c.</filename> A decoder needs to open
a channel FIFO with <function> aout_CreateFifo </function>, and
then write the data to the buffer. The buffer is in <parameter>
p_aout_fifo->buffer + p_aout_fifo->l_end_frame </parameter>
* <constant> ADEC_FRAME_SIZE</constant>.
</para>
</sect1>
<sect1> <title> How to write an audio output plugin </title>
<para>
[This API is subject to change in the very near future.] Have a look at
<filename> plugins/dsp/aout_dsp.c</filename>. You need to write six
functions :
</para>
<itemizedlist>
<listitem> <para> <type> int </type> <function> aout_Probe </function>
<parameter> ( probedata_t *p_data ) </parameter> :
Returns a score between 0 and 999 to tell whether the plugin
can be used. <parameter> p_data </parameter> is currently
unused.
</para> </listitem>
<listitem> <para> <type> int </type> <function> aout_Open </function>
<parameter> ( aout_thread_t *p_aout ) </parameter> :
Opens the audio device.
</para> </listitem>
<listitem> <para> <type> int </type> <function> aout_SetFormat
</function> <parameter> ( aout_thread_t *p_aout ) </parameter> :
Sets the output format, the number of channels, and the output
rate.
</para> </listitem>
<listitem> <para> <type> long </type> <function> aout_GetBufInfo
</function> <parameter> ( aout_thread_t *p_aout,
long l_buffer_limit ) </parameter> :
Gets the status of the audio buffer.
</para> </listitem>
<listitem> <para> <function> aout_Play </function> <parameter>
( aout_thread_t *p_aout, byte_t *buffer, int i_size )
</parameter> :
Writes the audio output buffer to the audio device.
</para> </listitem>
<listitem> <para> <function> aout_Close </function> <parameter>
( aout_thread_t *p_aout ) </parameter> :
Closes the audio device.
</para> </listitem>
</itemizedlist>
</sect1>
</chapter>
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