Aulib::ResamplerSdl Class Reference

SDL_AudioStream resampler. More...

#include <ResamplerSdl.h>

Inheritance diagram for Aulib::ResamplerSdl:

Public Member Functions
	ResamplerSdl ()
	~ResamplerSdl () override
Public Member Functions inherited from Aulib::Resampler
	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
void	doResampling (float dst[], const float src[], int &dstLen, int &srcLen) override
auto	adjustForOutputSpec (int dstRate, int srcRate, int channels) -> int override
	Change sample rate and amount of channels. More...
void	doDiscardPendingSamples () override
	Discard any internally held samples. More...
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

SDL_AudioStream resampler.

This uses the built-in resampling functionality of SDL (through the SDL_AudioStream API) and has no external dependencies. Requires at least SDL 2.0.7. Note that SDL can be built to use libsamplerate instead of its own resampler. There's no way to detect whether this is the case or not.

It usually makes no sense to use this resampler, unless you have a specific need to use SDL's resampler and you know that the SDL version you're running on was not built with libsamplerate support. If you do want libsamplerate, then you can just use Aulib::ResamplerSrc instead.

Constructor & Destructor Documentation

ResamplerSdl()

Aulib::ResamplerSdl::ResamplerSdl

(

)

~ResamplerSdl()

Aulib::ResamplerSdl::~ResamplerSdl ( )

override

Member Function Documentation

adjustForOutputSpec()

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

overrideprotectedvirtual

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.

Implements Aulib::Resampler.

doDiscardPendingSamples()

void Aulib::ResamplerSdl::doDiscardPendingSamples ( )

overrideprotectedvirtual

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.

Implements Aulib::Resampler.

doResampling()

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

overrideprotectedvirtual

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.

Implements Aulib::Resampler.