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+.. 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