DVB Audio Device

DVB Audio Device
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Audio Data Types
Audio Function Calls

The DVB audio device controls the MPEG2 audio decoder of the DVB hardware. It can be accessed through /dev/dvb/adapter?/audio?. Data types and and ioctl definitions can be accessed by including linux/dvb/audio.h in your application.

Please note that some DVB cards don’t have their own MPEG decoder, which results in the omission of the audio and video device.

These ioctls were also used by V4L2 to control MPEG decoders implemented in V4L2. The use of these ioctls for that purpose has been made obsolete and proper V4L2 ioctls or controls have been created to replace that functionality.

Audio Data Types

audio_stream_source_t
audio_play_state_t
audio_channel_select_t
struct audio_status
struct audio_mixer
audio encodings
struct audio_karaoke
audio attributes

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

audio_stream_source_t

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_t

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_t

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;

struct 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;

struct 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;

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

struct 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) ⋆/

Audio Function Calls

open()

DESCRIPTION

This system call opens a named audio device (e.g. /dev/dvb/adapter0/audio0) for subsequent use. When an open() call has succeeded, the device will be ready for use. The significance of blocking or non-blocking mode is described in the documentation for functions where there is a difference. It does not affect the semantics of the open() call itself. A device opened in blocking mode can later be put into non-blocking mode (and vice versa) using the F_SETFL command of the fcntl system call. This is a standard system call, documented in the Linux manual page for fcntl. Only one user can open the Audio Device in O_RDWR mode. All other attempts to open the device in this mode will fail, and an error code will be returned. If the Audio Device is opened in O_RDONLY mode, the only ioctl call that can be used is AUDIO_GET_STATUS. All other call will return with an error code.

SYNOPSIS

int open(const char ⋆deviceName, int flags);

PARAMETERS

const char *deviceName	Name of specific audio device.
int flags	A bit-wise OR of the following flags:
	O_RDONLY read-only access
	O_RDWR read/write access
	O_NONBLOCK open in non-blocking mode
	(blocking mode is the default)

RETURN VALUE

ENODEV	Device driver not loaded/available.
EBUSY	Device or resource busy.
EINVAL	Invalid argument.

close()

DESCRIPTION

This system call closes a previously opened audio device.

SYNOPSIS

int close(int fd);

PARAMETERS

int fd

File descriptor returned by a previous call to open().

RETURN VALUE

EBADF

fd is not a valid open file descriptor.

write()

DESCRIPTION

This system call can only be used if AUDIO_SOURCE_MEMORY is selected in the ioctl call AUDIO_SELECT_SOURCE. The data provided shall be in PES format. If O_NONBLOCK is not specified the function will block until buffer space is available. The amount of data to be transferred is implied by count.

SYNOPSIS

size_t write(int fd, const void ⋆buf, size_t count);

PARAMETERS

int fd	File descriptor returned by a previous call to open().
void *buf	Pointer to the buffer containing the PES data.
size_t count	Size of buf.

RETURN VALUE

EPERM	Mode AUDIO_SOURCE_MEMORY not selected.
ENOMEM	Attempted to write more data than the internal buffer can hold.
EBADF	fd is not a valid open file descriptor.

AUDIO_STOP

DESCRIPTION

This ioctl call asks the Audio Device to stop playing the current stream.

SYNOPSIS

int ioctl(int fd, int request = AUDIO_STOP);

PARAMETERS

int fd	File descriptor returned by a previous call to open().
int request	Equals AUDIO_STOP for this command.

RETURN VALUE

On success 0 is returned, on error -1 and the errno variable is set appropriately. The generic error codes are described at the Generic Error Codes chapter.

AUDIO_PLAY

DESCRIPTION

This ioctl call asks the Audio Device to start playing an audio stream from the selected source.

SYNOPSIS

int ioctl(int fd, int request = AUDIO_PLAY);

PARAMETERS

int fd	File descriptor returned by a previous call to open().
int request	Equals AUDIO_PLAY for this command.

RETURN VALUE

On success 0 is returned, on error -1 and the errno variable is set appropriately. The generic error codes are described at the Generic Error Codes chapter.

AUDIO_PAUSE

DESCRIPTION

This ioctl call suspends the audio stream being played. Decoding and playing are paused. It is then possible to restart again decoding and playing process of the audio stream using AUDIO_CONTINUE command.

If AUDIO_SOURCE_MEMORY is selected in the ioctl call AUDIO_SELECT_SOURCE, the DVB-subsystem will not decode (consume) any more data until the ioctl call AUDIO_CONTINUE or AUDIO_PLAY is performed.

SYNOPSIS

int ioctl(int fd, int request = AUDIO_PAUSE);

PARAMETERS

int fd	File descriptor returned by a previous call to open().
int request	Equals AUDIO_PAUSE for this command.

RETURN VALUE

On success 0 is returned, on error -1 and the errno variable is set appropriately. The generic error codes are described at the Generic Error Codes chapter.

AUDIO_CONTINUE

DESCRIPTION

This ioctl restarts the decoding and playing process previously paused with AUDIO_PAUSE command.

It only works if the stream were previously stopped with AUDIO_PAUSE

SYNOPSIS

int ioctl(int fd, int request = AUDIO_CONTINUE);

PARAMETERS

int fd	File descriptor returned by a previous call to open().
int request	Equals AUDIO_CONTINUE for this command.

RETURN VALUE

On success 0 is returned, on error -1 and the errno variable is set appropriately. The generic error codes are described at the Generic Error Codes chapter.

AUDIO_SELECT_SOURCE

DESCRIPTION

This ioctl call informs the audio device which source shall be used for the input data. The possible sources are demux or memory. If AUDIO_SOURCE_MEMORY is selected, the data is fed to the Audio Device through the write command.

SYNOPSIS

int ioctl(int fd, int request = AUDIO_SELECT_SOURCE, audio_stream_source_t source);

PARAMETERS

int fd	File descriptor returned by a previous call to open().
int request	Equals AUDIO_SELECT_SOURCE for this command.
audio_stream_source_t source	Indicates the source that shall be used for the Audio stream.

RETURN VALUE

On success 0 is returned, on error -1 and the errno variable is set appropriately. The generic error codes are described at the Generic Error Codes chapter.

AUDIO_SET_MUTE

DESCRIPTION

This ioctl is for DVB devices only. To control a V4L2 decoder use the V4L2 VIDIOC_DECODER_CMD with the V4L2_DEC_CMD_START_MUTE_AUDIO flag instead.

This ioctl call asks the audio device to mute the stream that is currently being played.

SYNOPSIS

int ioctl(int fd, int request = AUDIO_SET_MUTE, boolean state);

PARAMETERS

int fd	File descriptor returned by a previous call to open().
int request	Equals AUDIO_SET_MUTE for this command.
boolean state	Indicates if audio device shall mute or not.
	TRUE Audio Mute
	FALSE Audio Un-mute

RETURN VALUE

On success 0 is returned, on error -1 and the errno variable is set appropriately. The generic error codes are described at the Generic Error Codes chapter.

AUDIO_SET_AV_SYNC

DESCRIPTION

This ioctl call asks the Audio Device to turn ON or OFF A/V synchronization.

SYNOPSIS

int ioctl(int fd, int request = AUDIO_SET_AV_SYNC, boolean state);

PARAMETERS

int fd	File descriptor returned by a previous call to open().
int request	Equals AUDIO_AV_SYNC for this command.
boolean state	Tells the DVB subsystem if A/V synchronization shall be ON or OFF.
	TRUE AV-sync ON
	FALSE AV-sync OFF

RETURN VALUE

On success 0 is returned, on error -1 and the errno variable is set appropriately. The generic error codes are described at the Generic Error Codes chapter.

AUDIO_SET_BYPASS_MODE

DESCRIPTION

This ioctl call asks the Audio Device to bypass the Audio decoder and forward the stream without decoding. This mode shall be used if streams that can’t be handled by the DVB system shall be decoded. Dolby DigitalTM streams are automatically forwarded by the DVB subsystem if the hardware can handle it.

SYNOPSIS

int ioctl(int fd, int request = AUDIO_SET_BYPASS_MODE, boolean mode);

PARAMETERS

int fd	File descriptor returned by a previous call to open().
int request	Equals AUDIO_SET_BYPASS_MODE for this command.
boolean mode	Enables or disables the decoding of the current Audio stream in the DVB subsystem.
	TRUE Bypass is disabled
	FALSE Bypass is enabled

RETURN VALUE

On success 0 is returned, on error -1 and the errno variable is set appropriately. The generic error codes are described at the Generic Error Codes chapter.

AUDIO_CHANNEL_SELECT

DESCRIPTION

This ioctl is for DVB devices only. To control a V4L2 decoder use the V4L2 V4L2_CID_MPEG_AUDIO_DEC_PLAYBACK control instead.

This ioctl call asks the Audio Device to select the requested channel if possible.

SYNOPSIS

int ioctl(int fd, int request = AUDIO_CHANNEL_SELECT, audio_channel_select_t);

PARAMETERS

int fd	File descriptor returned by a previous call to open().
int request	Equals AUDIO_CHANNEL_SELECT for this command.
audio_channel_select_t ch	Select the output format of the audio (mono left/right, stereo).

RETURN VALUE

On success 0 is returned, on error -1 and the errno variable is set appropriately. The generic error codes are described at the Generic Error Codes chapter.

AUDIO_BILINGUAL_CHANNEL_SELECT

DESCRIPTION

This ioctl is obsolete. Do not use in new drivers. It has been replaced by the V4L2 V4L2_CID_MPEG_AUDIO_DEC_MULTILINGUAL_PLAYBACK control for MPEG decoders controlled through V4L2.

This ioctl call asks the Audio Device to select the requested channel for bilingual streams if possible.

SYNOPSIS

int ioctl(int fd, int request = AUDIO_BILINGUAL_CHANNEL_SELECT, audio_channel_select_t);

PARAMETERS

int fd	File descriptor returned by a previous call to open().
int request	Equals AUDIO_BILINGUAL_CHANNEL_SELECT for this command.
audio_channel_select_t ch	Select the output format of the audio (mono left/right, stereo).

RETURN VALUE

On success 0 is returned, on error -1 and the errno variable is set appropriately. The generic error codes are described at the Generic Error Codes chapter.

AUDIO_GET_PTS

DESCRIPTION

This ioctl is obsolete. Do not use in new drivers. If you need this functionality, then please contact the linux-media mailing list (https://linuxtv.org/lists.php).

This ioctl call asks the Audio Device to return the current PTS timestamp.

SYNOPSIS

int ioctl(int fd, int request = AUDIO_GET_PTS, __u64 *pts);

PARAMETERS

int fd

File descriptor returned by a previous call to open().

int request

Equals AUDIO_GET_PTS for this command.

__u64 *pts

Returns the 33-bit timestamp as defined in ITU T-REC-H.222.0 / ISO/IEC 13818-1.

The PTS should belong to the currently played frame if possible, but may also be a value close to it like the PTS of the last decoded frame or the last PTS extracted by the PES parser.

RETURN VALUE

On success 0 is returned, on error -1 and the errno variable is set appropriately. The generic error codes are described at the Generic Error Codes chapter.

AUDIO_GET_STATUS

DESCRIPTION

This ioctl call asks the Audio Device to return the current state of the Audio Device.

SYNOPSIS

int ioctl(int fd, int request = AUDIO_GET_STATUS, struct audio_status ⋆status);

PARAMETERS

int fd	File descriptor returned by a previous call to open().
int request	Equals AUDIO_GET_STATUS for this command.
struct audio_status *status	Returns the current state of Audio Device.

RETURN VALUE

On success 0 is returned, on error -1 and the errno variable is set appropriately. The generic error codes are described at the Generic Error Codes chapter.

AUDIO_GET_CAPABILITIES

DESCRIPTION

This ioctl call asks the Audio Device to tell us about the decoding capabilities of the audio hardware.

SYNOPSIS

int ioctl(int fd, int request = AUDIO_GET_CAPABILITIES, unsigned int ⋆cap);

PARAMETERS

int fd	File descriptor returned by a previous call to open().
int request	Equals AUDIO_GET_CAPABILITIES for this command.
unsigned int *cap	Returns a bit array of supported sound formats.

RETURN VALUE

On success 0 is returned, on error -1 and the errno variable is set appropriately. The generic error codes are described at the Generic Error Codes chapter.

AUDIO_CLEAR_BUFFER

DESCRIPTION

This ioctl call asks the Audio Device to clear all software and hardware buffers of the audio decoder device.

SYNOPSIS

int ioctl(int fd, int request = AUDIO_CLEAR_BUFFER);

PARAMETERS

int fd	File descriptor returned by a previous call to open().
int request	Equals AUDIO_CLEAR_BUFFER for this command.

RETURN VALUE

On success 0 is returned, on error -1 and the errno variable is set appropriately. The generic error codes are described at the Generic Error Codes chapter.

AUDIO_SET_ID

DESCRIPTION

This ioctl selects which sub-stream is to be decoded if a program or system stream is sent to the video device. If no audio stream type is set the id has to be in [0xC0,0xDF] for MPEG sound, in [0x80,0x87] for AC3 and in [0xA0,0xA7] for LPCM. More specifications may follow for other stream types. If the stream type is set the id just specifies the substream id of the audio stream and only the first 5 bits are recognized.

SYNOPSIS

int ioctl(int fd, int request = AUDIO_SET_ID, int id);

PARAMETERS

int fd	File descriptor returned by a previous call to open().
int request	Equals AUDIO_SET_ID for this command.
int id	audio sub-stream id

RETURN VALUE

On success 0 is returned, on error -1 and the errno variable is set appropriately. The generic error codes are described at the Generic Error Codes chapter.

AUDIO_SET_MIXER

DESCRIPTION

This ioctl lets you adjust the mixer settings of the audio decoder.

SYNOPSIS

int ioctl(int fd, int request = AUDIO_SET_MIXER, audio_mixer_t ⋆mix);

PARAMETERS

int fd	File descriptor returned by a previous call to open().
int request	Equals AUDIO_SET_ID for this command.
audio_mixer_t *mix	mixer settings.

RETURN VALUE

On success 0 is returned, on error -1 and the errno variable is set appropriately. The generic error codes are described at the Generic Error Codes chapter.

AUDIO_SET_STREAMTYPE

DESCRIPTION

This ioctl tells the driver which kind of audio stream to expect. This is useful if the stream offers several audio sub-streams like LPCM and AC3.

SYNOPSIS

int ioctl(fd, int request = AUDIO_SET_STREAMTYPE, int type);

PARAMETERS

int fd	File descriptor returned by a previous call to open().
int request	Equals AUDIO_SET_STREAMTYPE for this command.
int type	stream type

RETURN VALUE

On success 0 is returned, on error -1 and the errno variable is set appropriately. The generic error codes are described at the Generic Error Codes chapter.

EINVAL

type is not a valid or supported stream type.

AUDIO_SET_EXT_ID

DESCRIPTION

This ioctl can be used to set the extension id for MPEG streams in DVD playback. Only the first 3 bits are recognized.

SYNOPSIS

int ioctl(fd, int request = AUDIO_SET_EXT_ID, int id);

PARAMETERS

int fd	File descriptor returned by a previous call to open().
int request	Equals AUDIO_SET_EXT_ID for this command.
int id	audio sub_stream_id

RETURN VALUE

On success 0 is returned, on error -1 and the errno variable is set appropriately. The generic error codes are described at the Generic Error Codes chapter.

EINVAL

id is not a valid id.

AUDIO_SET_ATTRIBUTES

DESCRIPTION

This ioctl is intended for DVD playback and allows you to set certain information about the audio stream.

SYNOPSIS

int ioctl(fd, int request = AUDIO_SET_ATTRIBUTES, audio_attributes_t attr );

PARAMETERS

int fd	File descriptor returned by a previous call to open().
int request	Equals AUDIO_SET_ATTRIBUTES for this command.
audio_attributes_t attr	audio attributes according to section ??

RETURN VALUE

On success 0 is returned, on error -1 and the errno variable is set appropriately. The generic error codes are described at the Generic Error Codes chapter.

EINVAL

attr is not a valid or supported attribute setting.

AUDIO_SET_KARAOKE

DESCRIPTION

This ioctl allows one to set the mixer settings for a karaoke DVD.

SYNOPSIS

int ioctl(fd, int request = AUDIO_SET_KARAOKE, audio_karaoke_t ⋆karaoke);

PARAMETERS

int fd	File descriptor returned by a previous call to open().
int request	Equals AUDIO_SET_KARAOKE for this command.
audio_karaoke_t *karaoke	karaoke settings according to section ??.

RETURN VALUE

On success 0 is returned, on error -1 and the errno variable is set appropriately. The generic error codes are described at the Generic Error Codes chapter.

EINVAL

karaoke is not a valid or supported karaoke setting.