6.3.1. Audio Data Types

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

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.

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.

audio_play_state

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

typedef enum {
    AUDIO_STOPPED,
    AUDIO_PLAYING,
    AUDIO_PAUSED
} audio_play_state_t;

audio_channel_select

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

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

audio_status

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

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;

audio_mixer

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

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

6.3.1.1. audio encodings

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

#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