Portable Sound Hardware Abstraction
[Sound Device Port]

Detailed Description

This section describes lower level abstraction for sound device hardware. Application normally uses the higher layer Sound Device Port abstraction since it works seamlessly with Media Ports Framework.

The sound hardware abstraction basically runs asychronously, and application must register callbacks to be called to receive/ supply audio frames from/to the sound hardware.

A full duplex sound stream (created with pjmedia_snd_open()) requires application to supply two callbacks:

rec_cb callback to be called when it has finished capturing one media frame, and
play_cb callback to be called when it needs media frame to be played to the sound playback hardware.

Half duplex sound stream (created with pjmedia_snd_open_rec() or pjmedia_snd_open_player()) will only need one of the callback to be specified.

After sound stream is created, application need to call pjmedia_snd_stream_start() to start capturing/playing back media frames from/to the sound device.

Typedef Documentation

typedef struct pjmedia_snd_stream pjmedia_snd_stream

Opaque data type for audio stream.

typedef pj_status_t(* pjmedia_snd_play_cb)(void *user_data,pj_uint32_t timestamp,void *output,unsigned size)

This callback is called by player stream when it needs additional data to be played by the device. Application must fill in the whole of output buffer with sound samples.

Parameters:

	user_data	User data associated with the stream.
	timestamp	Timestamp, in samples.
	output	Buffer to be filled out by application.
	size	The size requested in bytes, which will be equal to the size of one whole packet.

Returns:: Non-zero to stop the stream.

typedef pj_status_t(* pjmedia_snd_rec_cb)(void *user_data,pj_uint32_t timestamp,void *input,unsigned size)

This callback is called by recorder stream when it has captured the whole packet worth of audio samples.

Parameters:

	user_data	User data associated with the stream.
	timestamp	Timestamp, in samples.
	output	Buffer containing the captured audio samples.
	size	The size of the data in the buffer, in bytes.

Returns:: Non-zero to stop the stream.

Function Documentation

pj_status_t pjmedia_snd_init ( pj_pool_factory * factory )

Init the sound library.

Parameters:

factory

The sound factory.

Returns:: Zero on success.

int pjmedia_snd_get_dev_count ( void )

Get the number of devices detected by the library.

Returns:: Number of devices.

const pjmedia_snd_dev_info* pjmedia_snd_get_dev_info ( unsigned index )

Get device info.

Parameters:

index

The index of the device, which should be in the range from zero to pjmedia_snd_get_dev_count - 1.

pj_status_t pjmedia_snd_set_latency	(	unsigned	input_latency,
		unsigned	output_latency
	)

Set sound device latency, this function must be called before sound device opened, or otherwise default latency setting will be used,

See also:: PJMEDIA_SND_DEFAULT_REC_LATENCY & PJMEDIA_SND_DEFAULT_PLAY_LATENCY.

Choosing latency value is not straightforward, it should accomodate both minimum latency and stability. Lower latency tends to cause sound device less reliable (producing audio dropouts) on CPU load disturbance. Moreover, the best latency setting may vary based on many aspects, e.g: sound card, CPU, OS, kernel, etc.

Parameters:

	input_latency	The latency of input device, in ms, set to 0 for default PJMEDIA_SND_DEFAULT_REC_LATENCY.
	output_latency	The latency of output device, in ms, set to 0 for default PJMEDIA_SND_DEFAULT_PLAY_LATENCY.

Returns:: PJ_SUCCESS on success.

pj_status_t pjmedia_snd_open	(	int	rec_id,
		int	play_id,
		unsigned	clock_rate,
		unsigned	channel_count,
		unsigned	samples_per_frame,
		unsigned	bits_per_sample,
		pjmedia_snd_rec_cb	rec_cb,
		pjmedia_snd_play_cb	play_cb,
		void *	user_data,
		pjmedia_snd_stream **	p_snd_strm
	)

Create sound stream for both capturing audio and audio playback, from the same device. This is the recommended way to create simultaneous recorder and player streams (instead of creating separate capture and playback streams), because it works on backends that does not allow a device to be opened more than once.

Parameters:

	rec_id	Device index for recorder/capture stream, or -1 to use the first capable device.
	play_id	Device index for playback stream, or -1 to use the first capable device.
	clock_rate	Sound device's clock rate to set.
	channel_count	Set number of channels, 1 for mono, or 2 for stereo. The channel count determines the format of the frame.
	samples_per_frame	Number of samples per frame.
	bits_per_sample	Set the number of bits per sample. The normal value for this parameter is 16 bits per sample.
	rec_cb	Callback to handle captured audio samples.
	play_cb	Callback to be called when the sound player needs more audio samples to play.
	user_data	User data to be associated with the stream.
	p_snd_strm	Pointer to receive the stream instance.

Returns:: PJ_SUCCESS on success.

pj_status_t pjmedia_snd_open_rec	(	int	index,
		unsigned	clock_rate,
		unsigned	channel_count,
		unsigned	samples_per_frame,
		unsigned	bits_per_sample,
		pjmedia_snd_rec_cb	rec_cb,
		void *	user_data,
		pjmedia_snd_stream **	p_snd_strm
	)

Create a unidirectional audio stream for capturing audio samples from the sound device.

Parameters:

	index	Device index, or -1 to let the library choose the first available device.
	clock_rate	Sound device's clock rate to set.
	channel_count	Set number of channels, 1 for mono, or 2 for stereo. The channel count determines the format of the frame.
	samples_per_frame	Number of samples per frame.
	bits_per_sample	Set the number of bits per sample. The normal value for this parameter is 16 bits per sample.
	rec_cb	Callback to handle captured audio samples.
	user_data	User data to be associated with the stream.
	p_snd_strm	Pointer to receive the stream instance.

Returns:: PJ_SUCCESS on success.

pj_status_t pjmedia_snd_open_player	(	int	index,
		unsigned	clock_rate,
		unsigned	channel_count,
		unsigned	samples_per_frame,
		unsigned	bits_per_sample,
		pjmedia_snd_play_cb	play_cb,
		void *	user_data,
		pjmedia_snd_stream **	p_snd_strm
	)

Create a unidirectional audio stream for playing audio samples to the sound device.

Parameters:

	index	Device index, or -1 to let the library choose the first available device.
	clock_rate	Sound device's clock rate to set.
	channel_count	Set number of channels, 1 for mono, or 2 for stereo. The channel count determines the format of the frame.
	samples_per_frame	Number of samples per frame.
	bits_per_sample	Set the number of bits per sample. The normal value for this parameter is 16 bits per sample.
	play_cb	Callback to be called when the sound player needs more audio samples to play.
	user_data	User data to be associated with the stream.
	p_snd_strm	Pointer to receive the stream instance.

Returns:: PJ_SUCCESS on success.

pj_status_t pjmedia_snd_stream_get_info	(	pjmedia_snd_stream *	strm,
		pjmedia_snd_stream_info *	pi
	)

Get information about live stream.

Parameters:

	strm	The stream to be queried.
	pi	Pointer to stream information to be filled up with information about the stream.

Returns:: PJ_SUCCESS on success or the appropriate error code.

pj_status_t pjmedia_snd_stream_start ( pjmedia_snd_stream * stream )

Start the stream.

Parameters:

stream

The recorder or player stream.

Returns:: Zero on success.

pj_status_t pjmedia_snd_stream_stop ( pjmedia_snd_stream * stream )

Stop the stream.

Parameters:

stream

The recorder or player stream.

Returns:: Zero on success.

pj_status_t pjmedia_snd_stream_close ( pjmedia_snd_stream * stream )

Destroy the stream.

Parameters:

stream

The recorder of player stream.

Returns:: Zero on success.

pj_status_t pjmedia_snd_deinit ( void )

Deinitialize sound library.

Returns:: Zero on success.

Portable Sound Hardware Abstraction [Sound Device Port]

Detailed Description

Data Structures

Typedefs

Functions

Typedef Documentation

Function Documentation

Portable Sound Hardware Abstraction
[Sound Device Port]