BackgroundAudioMixerInput Class Reference

Implements an emulated AudioOutputBase and feeds resampled data from it up to an input of an AudioOutputMixer object. More...

#include <BackgroundAudioMixer.h>

Inheritance diagram for BackgroundAudioMixerInput:

Collaboration diagram for BackgroundAudioMixerInput:

Public Member Functions
	BackgroundAudioMixerInput (int outputRate, size_t outputBufferWords)
	Create a mixer with a defined sample rate and buffer size.
virtual bool	setBuffers (size_t buffers, size_t bufferWords, int32_t silenceSample=0) override
	Set the size and number of the resample buffers before begin
virtual bool	setBitsPerSample (int bps) override
	Set the bits per sample for the emulated output. Only 16-bit supported.
virtual bool	setFrequency (int freq) override
	Set the sample rate (LRCLK/WS) of the emulated interface. Can be called while running.
virtual bool	setStereo (bool stereo=true) override
	Set mono or stereo mode. Only stereo supported.
virtual bool	begin () override
	Start the emulated interface.
virtual bool	end () override
	Stop the mixer input leg, not implemented.
virtual bool	getUnderflow () override
	Determine if there was an underflow since the last time this was called. Cleared on read.
virtual void	onTransmit (void(*cb)(void *), void *cbData) override
	Set the callback function to be called every mixer buffer completion.
virtual size_t	write (uint8_t)
	Write single byte to I2S buffers. Not supported.
virtual size_t	write (const uint8_t *buffer, size_t size) override
	Write data to the input leg interface. Will not block and may write less than requested.
virtual int	availableForWrite () override
	Determine the number of bytes we can write to the resample buffers at this instant.

Friends
template<size_t >
class	BackgroundAudioMixer

Detailed Description

Implements an emulated AudioOutputBase and feeds resampled data from it up to an input of an AudioOutputMixer object.

The mixer input will buffer output from one audio source and resample to the mixer frequency so it can be summed up and output.

Each input will have a buffer ready to be summed with the others. The mixer will take the pointers to this and do the sum operation w/o actually copying it out. As data is read from the mixerInputBuffer, it will be repopulated with (resampled) data from the source buffers. Every time the a full source buffer is read a CB will be fired, just like in the AudioBufferManager. (i.e. the mixedrinput will behave like the ABM for simplicity.)

In general an end user never need use this class directly and can just treat the input leg of the mixer as an ordinary audio output.

Member Function Documentation

availableForWrite()

virtual int BackgroundAudioMixerInput::availableForWrite ( )

inlineoverridevirtual

Determine the number of bytes we can write to the resample buffers at this instant.

Returns

Number of bytes available. May not be completely accurate

begin()

virtual bool BackgroundAudioMixerInput::begin ( )

inlineoverridevirtual

Start the emulated interface.

Doesn't actually start any hardware or interfaces (the AudioMixer owns the hardware device and combines multiple input legs. Does set up the resampling audio buffer for use by the mixer as needed.

Returns

True on success

end()

virtual bool BackgroundAudioMixerInput::end ( )

inlineoverridevirtual

Stop the mixer input leg, not implemented.

Returns

False on failure

getUnderflow()

virtual bool BackgroundAudioMixerInput::getUnderflow ( )

inlineoverridevirtual

Determine if there was an underflow since the last time this was called. Cleared on read.

Returns

True if an underflow occurred.

onTransmit()

virtual void BackgroundAudioMixerInput::onTransmit ( void(*)(void *)  cb, void *  cbData  )

inlineoverridevirtual

Set the callback function to be called every mixer buffer completion.

Parameters

[in]	cb	Callback function
[in]	cbData	Data to be passed to the callback function

setBitsPerSample()

virtual bool BackgroundAudioMixerInput::setBitsPerSample ( int  bps )

inlineoverridevirtual

Set the bits per sample for the emulated output. Only 16-bit supported.

Parameters

[in]

bps

Bits per sample, only 16-bit supported

Returns

True if successful

setBuffers()

virtual bool BackgroundAudioMixerInput::setBuffers ( size_t  buffers, size_t  bufferWords, int32_t  silenceSample = 0  )

inlineoverridevirtual

Set the size and number of the resample buffers before begin

Parameters

[in]	buffers	Number of I2S DMA buffers
[in]	bufferWords	Number of 32-bit words (i.e. a single stereo 16-bit sample) per each DMA buffer
[in]	silenceSample	Optional 32-bit value to send out in case of underflow, normally 0

Returns

True if parameters were successful

setFrequency()

virtual bool BackgroundAudioMixerInput::setFrequency ( int  freq )

inlineoverridevirtual

Set the sample rate (LRCLK/WS) of the emulated interface. Can be called while running.

This setting does not affect the actual resample rate of data sent up the chain to the mixer owner. This is only to allow a decoder to indicate whatever sample rate is required for incoming data.

Parameters

[in]

freq

New sampling frequency in hertz

Returns

True if succeeded

setStereo()

virtual bool BackgroundAudioMixerInput::setStereo ( bool  stereo = true )

inlineoverridevirtual

Set mono or stereo mode. Only stereo supported.

Parameters

[in]

stereo

Set to true for stereo (L/R) output

Returns

True if success

write() [1/2]

virtual size_t BackgroundAudioMixerInput::write ( const uint8_t *  buffer, size_t  size  )

inlineoverridevirtual

Write data to the input leg interface. Will not block and may write less than requested.

Parameters

[in]	buffer	Data to be written
[in]	size	Number of bytes to write.

Returns

Number of bytes actually written to the resample buffer

write() [2/2]

virtual size_t BackgroundAudioMixerInput::write ( uint8_t  )

inlinevirtual

Write single byte to I2S buffers. Not supported.

Returns

0 always

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The documentation for this class was generated from the following file:

• BackgroundAudioMixer.h