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

audio_karaoke

The ioctl AUDIO_SET_KARAOKE uses the following format:

typedef
struct audio_karaoke {
    int vocal1;
    int vocal2;
    int melody;
} audio_karaoke_t;

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.

audio_attributes

The following attributes can be set by a call to AUDIO_SET_ATTRIBUTES:

typedef uint16_t audio_attributes_t;
/*   bits: descr. */
/*   15-13 audio coding mode (0=ac3, 2=mpeg1, 3=mpeg2ext, 4=LPCM, 6=DTS, */
/*   12    multichannel extension */
/*   11-10 audio type (0=not spec, 1=language included) */
/*    9- 8 audio application mode (0=not spec, 1=karaoke, 2=surround) */
/*    7- 6 Quantization / DRC (mpeg audio: 1=DRC exists)(lpcm: 0=16bit,  */
/*    5- 4 Sample frequency fs (0=48kHz, 1=96kHz) */
/*    2- 0 number of audio channels (n+1 channels) */