Aulib::Resampler Class Reference

Abstract base class for audio resamplers. More...

#include <Resampler.h>

Inheritance diagram for Aulib::Resampler:

Public Member Functions
	Resampler ()
	Constructs an audio resampler. More...
virtual	~Resampler ()
	Resampler (const Resampler &)=delete
auto	operator= (const Resampler &) -> Resampler &=delete
void	setDecoder (std::shared_ptr< Decoder > decoder)
	Sets the decoder that is to be used as source. More...
auto	setSpec (int dstRate, int channels, int chunkSize) -> int
	Sets the target sample rate, channels and chuck size. More...
auto	currentRate () const -> int
auto	currentChannels () const -> int
auto	currentChunkSize () const -> int
auto	resample (float dst[], int dstLen) -> int
	Fills an output buffer with resampled audio samples. More...
void	discardPendingSamples ()
	Discards any samples that have not yet been retrieved with resample(). More...

Protected Member Functions
virtual auto	adjustForOutputSpec (int dstRate, int srcRate, int channels) -> int=0
	Change sample rate and amount of channels. More...
virtual void	doResampling (float dst[], const float src[], int &dstLen, int &srcLen)=0
virtual void	doDiscardPendingSamples ()=0
	Discard any internally held samples. More...

Detailed Description

Abstract base class for audio resamplers.

This class receives audio from an Decoder and resamples it to the requested sample rate.

Constructor & Destructor Documentation

Resampler() [1/2]

Aulib::Resampler::Resampler

(

)

Constructs an audio resampler.

~Resampler()

virtual Aulib::Resampler::~Resampler ( )

virtual

Resampler() [2/2]

Aulib::Resampler::Resampler ( const Resampler &  )

delete

Member Function Documentation

adjustForOutputSpec()

virtual auto Aulib::Resampler::adjustForOutputSpec ( int  dstRate, int  srcRate, int  channels  ) -> int

protectedpure virtual

Change sample rate and amount of channels.

This function must be implemented when subclassing. It is used to notify subclasses about changes in source and target sample rates, as well as the amount of channels in the audio.

Parameters

dstRate	Target sample rate (rate being resampled to.)
srcRate	Source sample rate (rate being resampled from.)
channels	Amount of channels in both the source as well as the target audio buffers.

Implemented in Aulib::ResamplerSdl, Aulib::ResamplerSox, Aulib::ResamplerSpeex, and Aulib::ResamplerSrc.

currentChannels()

auto Aulib::Resampler::currentChannels

(

)

const -> int

currentChunkSize()

auto Aulib::Resampler::currentChunkSize

(

)

const -> int

currentRate()

auto Aulib::Resampler::currentRate

(

)

const -> int

discardPendingSamples()

void Aulib::Resampler::discardPendingSamples

(

)

Discards any samples that have not yet been retrieved with resample().

This is especially useful after seeking the decoder to a different position and you want resample() to immediately give you samples from the new position rather than the ones from the old position that were previously resampled but not yet retrieved.

doDiscardPendingSamples()

virtual void Aulib::Resampler::doDiscardPendingSamples ( )

protectedpure virtual

Discard any internally held samples.

This function must be implemented when subclassing. It should discard any internally held samples. Note that even if you don't actually buffer any samples in your subclass but are using some external resampling library that you delegate resampling to, that external resampler might be holding samples in an internal buffer. Those will need to be discarded as well.

If none of the above applies, this can be implemented as an empty function.

Implemented in Aulib::ResamplerSdl, Aulib::ResamplerSox, Aulib::ResamplerSpeex, and Aulib::ResamplerSrc.

doResampling()

virtual void Aulib::Resampler::doResampling ( float  dst[], const float  src[], int &  dstLen, int &  srcLen  )

protectedpure virtual

This function must be implemented when subclassing. It must resample the audio contained in 'src' containing 'srcLen' samples, and store the resulting samples in 'dst', which has a capacity of at most 'dstLen' samples.

The 'src' buffer contains audio in either mono or stereo. Stereo is stored in interleaved format.

The source and target sample rates, as well as the amount of channels that are to be used must be those that were specified in the last call to the adjustForOutputSpec() function.

'dstLen' and 'srcLen' are both input as well as output parameters. The function must set 'dstLen' to the amount of samples that were actually stored in 'dst', and 'srcLen' to the amount of samples that were actually used from 'src'. For example, if in the following call:

 dstLen = 200;
 srcLen = 100;
 doResampling(dst, src, dstLen, srcLen);

the function resamples 98 samples from 'src', resulting in 196 samples which are stored in 'dst', the function must set 'srcLen' to 98 and 'dstLen' to 196.

So when implementing this function, you do not need to worry about using up all the available samples in 'src'. Simply resample as much audio from 'src' as you can in order to fill 'dst' as much as possible, and if there's anything left at the end that cannot be resampled, simply ignore it.

Implemented in Aulib::ResamplerSdl, Aulib::ResamplerSox, Aulib::ResamplerSpeex, and Aulib::ResamplerSrc.

operator=()

auto Aulib::Resampler::operator= ( const Resampler &  ) -> Resampler &=delete

delete

resample()

auto Aulib::Resampler::resample	(	float	dst[],
		int	dstLen
	)		-> int

Fills an output buffer with resampled audio samples.

Parameters

dst	Output buffer.
dstLen	Size of output buffer (amount of elements, not size in bytes.)

Returns

The amount of samples that were stored in the buffer. This can be smaller than 'dstLen' if the decoder has no more samples left.

setDecoder()

void Aulib::Resampler::setDecoder

(

std::shared_ptr< Decoder >

decoder

)

Sets the decoder that is to be used as source.

Parameters

decoder

The decoder to use as source. Must not be null.

setSpec()

auto Aulib::Resampler::setSpec	(	int	dstRate,
		int	channels,
		int	chunkSize
	)		-> int

Sets the target sample rate, channels and chuck size.

Parameters

dstRate	Wanted sample rate.
channels	Wanted amount of channels.
chunkSize	Specifies how many samples per channel to resample at most in each call to the resample() function. It is recommended to set this to the same value that was used as buffer size in the call to Aulib::init().