PTLib: PSoundChannel Class Reference

When instantiated, it selects the first plugin of the base class "PSoundChannel"

As an abstract class, this represents a sound schannel. Drivers for real, platform dependent sound hardware will be ancestors of this class and can be found in the plugins section of PTLib.

A sound channel is either playing or recording. If simultaneous playing and recording is desired, two instances of PSoundChannel must be created. It is an error for the same thread to attempt to both read and write audio data to once instance of a PSoundChannel class.

PSoundChanel instances are designed to be reentrant. The actual usage model employed is left to the developer. One model could be where one thread is responsible for construction, setup, opening and read/write operations. After creating and eventually opening the channel this thread is responsible for handling read/writes fast enough to avoid gaps in the generated audio stream.

Remaining operations may beinvoked from other threads. This includes Close() and actually gathering the necessary data to be sent to the device.

Besides the basic I/O task, the Read()/Write(() functions have well defined timing characteristics. When a PSoundChannel instance is used from Opal, the read/write operations are designed to also act as timers so as to nicely space the generated network packets of audio/ sound packets to the speaker.

Read and Writes of audio data to a PSoundChannel are blocking. The length of time required to read/write a block of audio from/to a PSoundChannel instance is equal to the time required for that block of audio to record/play. So for a sound rate of 8khz, 240 samples, it is going to take 30ms to do a read/write.

Since the Read()/Write(() functions have well defined timing characteristics; they are designed to also act as timers in a loop involving data transfers to/from the codecs.

The sound is buffered and the size and number of buffers should be set before playing/recording. Each call to Write() will use one buffer, so care needs to be taken not to use a large number of small writes but tailor the buffers to the size of each write you make.

Similarly for reading, an entire buffer must be read before any of it is available to a Read() call. Note that once a buffer is filled you can read it a byte at a time if desired, but as soon as all the data in the buffer is used returned, the next read will wait until the entire next buffer is read from the hardware. So again, tailor the number and size of buffers to the application. To avoid being blocked until the buffer fills, you can use the StartRecording() function to initiate the buffer filling, and the IsRecordingBufferFull() function to determine when the Read() function will no longer block.

Note that this sound channel is implicitly a linear PCM channel. No data conversion is performed on data to/from the channel.

Member Enumeration Documentation

anonymous enum

Enumerator:

MaxVolume

enum PSoundChannel::Directions

Enumerator:

Recorder
Player

Constructor & Destructor Documentation

PSoundChannel::PSoundChannel ( )

Create a sound channel.

PSoundChannel::PSoundChannel	(	const PString &	device,
		Directions	dir,
		unsigned	numChannels = `1`,
		unsigned	sampleRate = `8000`,
		unsigned	bitsPerSample = `16`
	)

Create a sound channel.

Create a reference to the sound drivers for the platform.

Parameters:

device	Name of sound driver/device
dir	Sound I/O direction
numChannels	Number of channels eg mono/stereo
sampleRate	Samples per second
bitsPerSample	Number of bits per sample

virtual PSoundChannel::~PSoundChannel ( ) [virtual]

Member Function Documentation

virtual PBoolean PSoundChannel::Abort ( ) [virtual]

Abort the background playing/recording of the sound channel.

There will be a logic assertion if you attempt to Abort a sound channel operation, when the device is currently closed.

Returns:: true if the sound has successfully been aborted.

virtual PBoolean PSoundChannel::AreAllRecordBuffersFull ( ) [virtual]

Determine if all of the record buffer allocated has been filled.

There is an implicit Abort() of the recording if this occurs and recording is stopped. The channel may need to be closed and opened again to start a new recording.

Returns:: true if the sound driver has filled a buffer.

virtual PBoolean PSoundChannel::Close ( ) [virtual]

Close the channel, shutting down the link to the data source.

Returns:: true if the channel successfully closed.

Reimplemented from PChannel.

static PSoundChannel* PSoundChannel::CreateChannel	(	const PString &	driverName,
		PPluginManager *	pluginMgr = `NULL`
	)			`[static]`

Create the sound channel that corresponds to the specified driver name.

Parameters:

driverName	Name of driver
pluginMgr	Plug in manager, use default if NULL

static PSoundChannel* PSoundChannel::CreateChannelByName	(	const PString &	deviceName,
		Directions	direction,
		PPluginManager *	pluginMgr = `NULL`
	)			`[static]`

Parameters:

deviceName	Name of device
direction	Direction for device (record or play)
pluginMgr	Plug in manager, use default if NULL

static PSoundChannel* PSoundChannel::CreateOpenedChannel	(	const PString &	driverName,
		const PString &	deviceName,
		Directions	direction,
		unsigned	numChannels = `1`,
		unsigned	sampleRate = `8000`,
		unsigned	bitsPerSample = `16`,
		PPluginManager *	pluginMgr = `NULL`
	)			`[static]`

Create an opened sound channel that corresponds to the specified names.

If the driverName parameter is an empty string or "*" then CreateChannelByName is used with the deviceName parameter which is assumed to be a value returned from GetAllDeviceNames().

Parameters:

driverName	Name of driver
deviceName	Name of device
direction	Direction for device (record or play)
numChannels	Number of channels 1=mon, 2=stereo
sampleRate	Sample rate
bitsPerSample	Bits per sample
pluginMgr	Plug in manager, use default if NULL

virtual PBoolean PSoundChannel::GetBuffers	(	PINDEX &	size,
		PINDEX &	count
	)			`[virtual]`

Get the internal buffers for the sound channel I/O.

Returns:: true if the buffer size were obtained.

virtual unsigned PSoundChannel::GetChannels ( ) const [virtual]

Get the number of channels (mono/stereo) in the sound.

static PString PSoundChannel::GetDefaultDevice ( Directions dir ) [static]

Get the name for the default sound devices/driver that is on this platform.

Note that a named device may not necessarily do both playing and recording so the arrays returned with the dir parameter in each value is not necessarily the same.

This will return a list of uniqie device names across all of the available drivers. If two drivers have identical names for devices, then the string returned will be of the form driver+'\t'+device.

Returns:: A platform dependent string for the sound player/recorder.

static PStringArray PSoundChannel::GetDeviceNames	(	Directions	direction,
		PPluginManager *	pluginMgr = `NULL`
	)			`[static]`

Get the list of all devices name for the default sound devices/driver that is on this platform.

Note that a named device may not necessarily do both playing and recording so the arrays returned with the dir parameter in each value is not necessarily the same.

Returns:: Platform dependent strings for the sound player/recorder.

Parameters:

direction	Direction for device (record or play)
pluginMgr	Plug in manager, use default if NULL

static PStringArray PSoundChannel::GetDeviceNames	(	const PString &	driverName,
		Directions	direction,
		PPluginManager *	pluginMgr = `NULL`
	)			`[inline, static]`

static PStringArray PSoundChannel::GetDriverNames ( PPluginManager * pluginMgr = NULL ) [static]

Get the list of available sound drivers (plug-ins).

Parameters:

pluginMgr

Plug in manager, use default if NULL

static PStringArray PSoundChannel::GetDriversDeviceNames	(	const PString &	driverName,
		Directions	direction,
		PPluginManager *	pluginMgr = `NULL`
	)			`[static]`

Get sound devices that correspond to the specified driver name.

If driverName is an empty string or the value "*" then GetAllDeviceNames() is used.

Parameters:

driverName	Name of driver
direction	Direction for device (record or play)
pluginMgr	Plug in manager, use default if NULL

virtual int PSoundChannel::GetHandle ( ) const [virtual]

Get the OS specific handle for the PSoundChannel.

Returns:: integer value of the handle.

Reimplemented from PChannel.

PINDEX PSoundChannel::GetLastReadCount ( ) const [virtual]

Return number of bytes read in last Read() call.

Reimplemented from PChannel.

virtual PINDEX PSoundChannel::GetLastWriteCount ( ) const [virtual]

Get number of bytes written in last Write() operation.

Reimplemented from PChannel.

virtual PString PSoundChannel::GetName ( ) const [virtual]

Get the name of the open channel.

Reimplemented from PChannel.

virtual unsigned PSoundChannel::GetSampleRate ( ) const [virtual]

Get the sample rate in samples per second.

virtual unsigned PSoundChannel::GetSampleSize ( ) const [virtual]

Get the sample size in bits per sample.

virtual PBoolean PSoundChannel::GetVolume ( unsigned & volume ) [virtual]

Get the volume of the play/read process.

The volume range is 0 == quiet, 100 == LOUDEST. The volume is a logarithmic scale mapped from the lowest gain possible on the device to the highest gain.

Returns:: true if there were no errors.

Parameters:

volume

Variable to receive volume level.

virtual PBoolean PSoundChannel::HasPlayCompleted ( ) [virtual]

Indicate if the sound play begun with PlayBuffer() or PlayFile() has completed.

Returns:: true if the sound has completed playing.

virtual PBoolean PSoundChannel::IsOpen ( ) const [virtual]

Test if this instance of PSoundChannel is open.

Returns:: true if this instance is open.

Reimplemented from PChannel.

virtual PBoolean PSoundChannel::IsRecordBufferFull ( ) [virtual]

Determine if a record buffer has been filled, so that the next Read() call will not block.

Provided that the amount of data read is less than the buffer size.

Returns:: true if the sound driver has filled a buffer.

virtual PBoolean PSoundChannel::Open	(	const PString &	device,
		Directions	dir,
		unsigned	numChannels = `1`,
		unsigned	sampleRate = `8000`,
		unsigned	bitsPerSample = `16`
	)			`[virtual]`

Open the specified device for playing or recording.

The device name is platform specific and is as returned in the GetDevices() function.

Returns:: true if the sound device is valid for playing/recording.

Parameters:

device	Name of sound driver/device
dir	Sound I/O direction
numChannels	Number of channels eg mono/stereo
sampleRate	Samples per second
bitsPerSample	Number of bits per sample

virtual PBoolean PSoundChannel::PlayFile	(	const PFilePath &	file,
		PBoolean	wait = `true`
	)			`[virtual]`

Play a sound file to the open device.

If the wait parameter is true then the function does not return until the file has been played. If false then the sound play is begun asynchronously and the function returns immediately.

Note if the driver is closed of the object destroyed then the sound play is aborted.

Also note that not all possible sounds and sound files are playable by this library. No format conversions between sound object and driver are performed.

Returns:: true if the sound is playing or has played.

Parameters:

file	Sound file to play.
wait	Flag to play sound synchronously.

virtual PBoolean PSoundChannel::PlaySound	(	const PSound &	sound,
		PBoolean	wait = `true`
	)			`[virtual]`

Play a sound to the open device.

If the wait parameter is true then the function does not return until the file has been played. If false then the sound play is begun asynchronously and the function returns immediately.

Note: if the driver is closed while playing the sound, the play operation stops immediately.

Also note that not all possible sounds and sound files are playable by this library. No format conversions between sound object and driver are performed.

Returns:: true if the sound is playing or has played.

Parameters:

sound	Sound to play.
wait	Flag to play sound synchronously.

virtual PBoolean PSoundChannel::Read	(	void *	buf,
		PINDEX	len
	)			`[virtual]`

Low level read from the channel.

This function may block until the requested number of characters were read or the read timeout was reached. The GetLastReadCount() function returns the actual number of bytes read.

It will generate a logical assertion if you attempt to read from a PSoundChannel that is setup for playing.

The GetErrorCode() function should be consulted after Read() returns false to determine what caused the failure.

Parameters:

	len	Nr of bytes to endeaveour to read from the sound device. If len equals the buffer size set by SetBuffers() it will block for (1000len)/(samplesizesamplerate) ms. Typically, the sample size is 2 bytes. If len == 0, this will return immediately, where the return value is equal to the value of IsOpen().
	buf	is a pointer to the empty data area, which will contain the data collected from the sound device. It is an error for this pointer to be NULL. A logical assert will be generated when buf is NULL.

Returns:: true indicates that at least one character was read from the channel. false means no bytes were read due to some I/O error, (which includes timeout or some other thread closed the device).

Parameters:

buf	Pointer to a block of memory to receive the read bytes.
len	Maximum number of bytes to read into the buffer.

Reimplemented from PChannel.

virtual PBoolean PSoundChannel::RecordFile ( const PFilePath & file ) [virtual]

Record into the platform dependent sound file all of the buffer's of sound data.

Use the SetBuffers() function to determine how long the recording will be made.

Note that this function will block until all of the data is buffered. If you wish to do this asynchronously, use StartRecording() and AreAllrecordBuffersFull() to determine when you can call RecordSound() without blocking.

Returns:: true if the sound has been recorded.

Parameters:

file

Sound file recorded

virtual PBoolean PSoundChannel::RecordSound ( PSound & sound ) [virtual]

Record into the sound object all of the buffer's of sound data.

Use the SetBuffers() function to determine how long the recording will be made.

For the Win32 platform, the most efficient way to record a PSound is to use the SetBuffers() function to set a single buffer of the desired size and then do the recording. For Linux OSS this can cause problems as the buffers are rounded up to a power of two, so to gain more accuracy you need a number of smaller buffers.

Returns:: true if the sound has been recorded.

Parameters:

sound

Sound recorded

virtual PBoolean PSoundChannel::SetBuffers	(	PINDEX	size,
		PINDEX	count = `2`
	)			`[virtual]`

Set the internal buffers for the sound channel I/O.

Note that with Linux OSS, the size is always rounded up to the nearest power of two, so 20000 => 32768.

Returns:: true if the sound device is valid for playing/recording.

Parameters:

size	Size of each buffer
count	Number of buffers

virtual PBoolean PSoundChannel::SetFormat	(	unsigned	numChannels = `1`,
		unsigned	sampleRate = `8000`,
		unsigned	bitsPerSample = `16`
	)			`[virtual]`

Set the format for play/record.

Note that linear PCM data is the only one supported at this time.

Note that if the PlayFile() function is used, this may be overridden by information in the file being played.

Returns:: true if the format is valid.

Parameters:

numChannels	Number of channels eg mono/stereo
sampleRate	Samples per second
bitsPerSample	Number of bits per sample

virtual PBoolean PSoundChannel::SetVolume ( unsigned volume ) [virtual]

Set the volume of the play/read process.

The volume range is 0 == quiet, 100 == LOUDEST. The volume is a logarithmic scale mapped from the lowest gain possible on the device to the highest gain

Returns:: true if there were no errors.

Parameters:

volume

New volume level

virtual PBoolean PSoundChannel::StartRecording ( ) [virtual]

Start filling record buffers.

The first call to Read() will also initiate the recording.

Returns:: true if the sound driver has successfully started recording.

virtual PBoolean PSoundChannel::WaitForAllRecordBuffersFull ( ) [virtual]

Block the thread until all of the record buffer allocated has been filled.

There is an implicit Abort() of the recording if this occurs and recording is stopped. The channel may need to be closed and opened again to start a new recording.

Returns:: true if the sound driver has filled a buffer.

virtual PBoolean PSoundChannel::WaitForPlayCompletion ( ) [virtual]

Block calling thread until the sound play begun with PlaySound() or PlayFile() has completed.

Returns:: true if the sound has successfully completed playing.

virtual PBoolean PSoundChannel::WaitForRecordBufferFull ( ) [virtual]

Block the thread until a record buffer has been filled, so that the next Read() call will not block.

Provided that the amount of data read is less than the buffer size.

Returns:: true if the sound driver has filled a buffer.

virtual PBoolean PSoundChannel::Write	(	const void *	buf,
		PINDEX	len,
		const void *	mark
	)			`[virtual]`

Low level write (or play) with watermark to the channel.

It will generate a logical assertion if you attempt write to a channel set up for recording.

Parameters:

	buf	is a pointer to the data to be written to the channel. It is an error for this pointer to be NULL. A logical assert will be generated when buf is NULL.
	len	Nr of bytes to send. If len equals the buffer size set by SetBuffers() it will block for (1000len)/(samplesizesamplerate) ms. Typically, the sample size is 2 bytes. If len == 0, this will return immediately, where the return value is equal to the value of IsOpen().
	mark	Unique identifer to identify the write

Returns:: PTrue if len bytes were written to the channel, otherwise PFalse. The GetErrorCode() function should be consulted after Write() returns PFalse to determine what caused the failure.

Parameters:

buf	Pointer to a block of memory to write.
len	Number of bytes to write.
mark	Unique Marker to identify write

Reimplemented from PChannel.

virtual PBoolean PSoundChannel::Write	(	const void *	buf,
		PINDEX	len
	)			`[virtual]`

Low level write (or play) to the channel.

It will generate a logical assertion if you attempt write to a channel set up for recording.

Parameters:

	buf	is a pointer to the data to be written to the channel. It is an error for this pointer to be NULL. A logical assert will be generated when buf is NULL.
	len	Nr of bytes to send. If len equals the buffer size set by SetBuffers() it will block for (1000len)/(samplesizesamplerate) ms. Typically, the sample size is 2 bytes. If len == 0, this will return immediately, where the return value is equal to the value of IsOpen().

Returns:: true if len bytes were written to the channel, otherwise false. The GetErrorCode() function should be consulted after Write() returns false to determine what caused the failure.

Reimplemented from PChannel.

Member Data Documentation

Directions PSoundChannel::activeDirection [protected]

This is the direction that this sound channel is opened for use in.

Should the user attempt to used this opened class instance in a direction opposite to that specified in activeDirection, an assert happens.

PSoundChannel Class Reference

Construction

Channel set up functions

Open functions

Public Member Functions

Protected Attributes

Detailed Description

Member Enumeration Documentation

Constructor & Destructor Documentation

Member Function Documentation

Member Data Documentation


Construction
enum	Directions { Recorder, Player }
	PSoundChannel ()
	Create a sound channel.
	PSoundChannel (const PString &device, Directions dir, unsigned numChannels=1, unsigned sampleRate=8000, unsigned bitsPerSample=16)
	Create a sound channel.
virtual	~PSoundChannel ()
Channel set up functions
enum	{ MaxVolume = 100 }
virtual PBoolean	SetFormat (unsigned numChannels=1, unsigned sampleRate=8000, unsigned bitsPerSample=16)
	Set the format for play/record.
virtual unsigned	GetChannels () const
	Get the number of channels (mono/stereo) in the sound.
virtual unsigned	GetSampleRate () const
	Get the sample rate in samples per second.
virtual unsigned	GetSampleSize () const
	Get the sample size in bits per sample.
virtual PBoolean	SetBuffers (PINDEX size, PINDEX count=2)
	Set the internal buffers for the sound channel I/O.
virtual PBoolean	GetBuffers (PINDEX &size, PINDEX &count)
	Get the internal buffers for the sound channel I/O.
virtual PBoolean	SetVolume (unsigned volume)
	Set the volume of the play/read process.
virtual PBoolean	GetVolume (unsigned &volume)
	Get the volume of the play/read process.
Open functions
virtual PBoolean	Open (const PString &device, Directions dir, unsigned numChannels=1, unsigned sampleRate=8000, unsigned bitsPerSample=16)
	Open the specified device for playing or recording.
virtual PBoolean	IsOpen () const
	Test if this instance of PSoundChannel is open.
virtual PBoolean	Close ()
	Close the channel, shutting down the link to the data source.
virtual int	GetHandle () const
	Get the OS specific handle for the PSoundChannel.
virtual PString	GetName () const
	Get the name of the open channel.
virtual PBoolean	Abort ()
	Abort the background playing/recording of the sound channel.
static PStringArray	GetDriverNames (PPluginManager *pluginMgr=NULL)
	Get the list of available sound drivers (plug-ins).
static PStringArray	GetDriversDeviceNames (const PString &driverName, Directions direction, PPluginManager *pluginMgr=NULL)
	Get sound devices that correspond to the specified driver name.
static PStringArray	GetDeviceNames (const PString &driverName, Directions direction, PPluginManager *pluginMgr=NULL)
static PSoundChannel *	CreateChannel (const PString &driverName, PPluginManager *pluginMgr=NULL)
	Create the sound channel that corresponds to the specified driver name.
static PSoundChannel *	CreateChannelByName (const PString &deviceName, Directions direction, PPluginManager *pluginMgr=NULL)
static PSoundChannel *	CreateOpenedChannel (const PString &driverName, const PString &deviceName, Directions direction, unsigned numChannels=1, unsigned sampleRate=8000, unsigned bitsPerSample=16, PPluginManager *pluginMgr=NULL)
	Create an opened sound channel that corresponds to the specified names.
static PString	GetDefaultDevice (Directions dir)
	Get the name for the default sound devices/driver that is on this platform.
static PStringArray	GetDeviceNames (Directions direction, PPluginManager *pluginMgr=NULL)
	Get the list of all devices name for the default sound devices/driver that is on this platform.
Public Member Functions
Play functions
virtual PBoolean	Write (const void *buf, PINDEX len)
	Low level write (or play) to the channel.
virtual PBoolean	Write (const void buf, PINDEX len, const void mark)
	Low level write (or play) with watermark to the channel.
virtual PINDEX	GetLastWriteCount () const
	Get number of bytes written in last Write() operation.
virtual PBoolean	PlaySound (const PSound &sound, PBoolean wait=true)
	Play a sound to the open device.
virtual PBoolean	PlayFile (const PFilePath &file, PBoolean wait=true)
	Play a sound file to the open device.
virtual PBoolean	HasPlayCompleted ()
	Indicate if the sound play begun with PlayBuffer() or PlayFile() has completed.
virtual PBoolean	WaitForPlayCompletion ()
	Block calling thread until the sound play begun with PlaySound() or PlayFile() has completed.
Record functions
virtual PBoolean	Read (void *buf, PINDEX len)
	Low level read from the channel.
PINDEX	GetLastReadCount () const
	Return number of bytes read in last Read() call.
virtual PBoolean	RecordSound (PSound &sound)
	Record into the sound object all of the buffer's of sound data.
virtual PBoolean	RecordFile (const PFilePath &file)
	Record into the platform dependent sound file all of the buffer's of sound data.
virtual PBoolean	StartRecording ()
	Start filling record buffers.
virtual PBoolean	IsRecordBufferFull ()
	Determine if a record buffer has been filled, so that the next Read() call will not block.
virtual PBoolean	AreAllRecordBuffersFull ()
	Determine if all of the record buffer allocated has been filled.
virtual PBoolean	WaitForRecordBufferFull ()
	Block the thread until a record buffer has been filled, so that the next Read() call will not block.
virtual PBoolean	WaitForAllRecordBuffersFull ()
	Block the thread until all of the record buffer allocated has been filled.
Protected Attributes
PSoundChannel *	baseChannel
Directions	activeDirection
	This is the direction that this sound channel is opened for use in.