.. Permission is granted to copy, distribute and/or modify this
.. document under the terms of the GNU Free Documentation License,
.. Version 1.1 or any later version published by the Free Software
.. Foundation, with no Invariant Sections, no Front-Cover Texts
.. and no Back-Cover Texts. A copy of the license is included at
.. Documentation/userspace-api/media/fdl-appendix.rst.
..
.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections

.. _audio_data_types:

****************
Audio Data Types
****************

This section describes the structures, data types and defines used when
talking to the audio device.

.. c:type:: audio_stream_source

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.


.. code-block:: c

    typedef enum {
	AUDIO_SOURCE_DEMUX,
	AUDIO_SOURCE_MEMORY
    } audio_stream_source_t;

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 ``write()`` system call.


.. c:type:: audio_play_state

The following values can be returned by the AUDIO_GET_STATUS call
representing the state of audio playback.


.. code-block:: c

    typedef enum {
	AUDIO_STOPPED,
	AUDIO_PLAYING,
	AUDIO_PAUSED
    } audio_play_state_t;


.. c:type:: audio_channel_select

The audio channel selected via AUDIO_CHANNEL_SELECT is determined by
the following values.


.. code-block:: c

    typedef enum {
	AUDIO_STEREO,
	AUDIO_MONO_LEFT,
	AUDIO_MONO_RIGHT,
	AUDIO_MONO,
	AUDIO_STEREO_SWAPPED
    } audio_channel_select_t;


.. c:type:: audio_status

The AUDIO_GET_STATUS call returns the following structure informing
about various states of the playback operation.


.. code-block:: c

    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;


.. c:type:: audio_mixer

The following structure is used by the AUDIO_SET_MIXER call to set the
audio volume.


.. code-block:: c

    typedef struct audio_mixer {
	unsigned int volume_left;
	unsigned int volume_right;
    } audio_mixer_t;


.. _audio_encodings:

audio encodings
===============

A call to AUDIO_GET_CAPABILITIES returns an unsigned integer with the
following bits set according to the hardwares capabilities.


.. code-block:: c

     #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
