Android APIs
Added in API level 14
public interface

SynthesisCallback

android.speech.tts.SynthesisCallback

Class Overview

A callback to return speech data synthesized by a text to speech engine. The engine can provide streaming audio by calling start(int, int, int), then audioAvailable(byte[], int, int) until all audio has been provided, then finally done(). error() can be called at any stage in the synthesis process to indicate that an error has occurred, but if the call is made after a call to done(), it might be discarded. done() must be called at the end of synthesis, regardless of errors. All methods can be only called on the synthesis thread.

Summary

Public Methods
abstract int audioAvailable(byte[] buffer, int offset, int length)
The service should call this method when synthesized audio is ready for consumption.
abstract int done()
The service should call this method when all the synthesized audio for a request has been passed to audioAvailable(byte[], int, int).
abstract void error(int errorCode)
The service should call this method if the speech synthesis fails.
abstract void error()
The service should call this method if the speech synthesis fails.
abstract int getMaxBufferSize()
abstract boolean hasFinished()
Check if done() was called or not.
abstract boolean hasStarted()
Check if start(int, int, int) was called or not.
abstract int start(int sampleRateInHz, int audioFormat, int channelCount)
The service should call this when it starts to synthesize audio for this request.

Public Methods

public abstract int audioAvailable (byte[] buffer, int offset, int length)

Added in API level 14

The service should call this method when synthesized audio is ready for consumption. This method should only be called on the synthesis thread, while in onSynthesizeText(SynthesisRequest, SynthesisCallback).

Parameters
buffer The generated audio data. This method will not hold on to buffer, so the caller is free to modify it after this method returns.
offset The offset into buffer where the audio data starts.
length The number of bytes of audio data in buffer. This must be less than or equal to the return value of getMaxBufferSize().
Returns
int SUCCESS, ERROR or STOPPED.

public abstract int done ()

Added in API level 14

The service should call this method when all the synthesized audio for a request has been passed to audioAvailable(byte[], int, int). This method should only be called on the synthesis thread, while in onSynthesizeText(SynthesisRequest, SynthesisCallback). This method has to be called if start(int, int, int) and/or error() was called.

Returns
int SUCCESS, ERROR or STOPPED.

public abstract void error (int errorCode)

Added in API level 21

The service should call this method if the speech synthesis fails. This method should only be called on the synthesis thread, while in onSynthesizeText(SynthesisRequest, SynthesisCallback).

Parameters
errorCode Error code to pass to the client. One of the ERROR_ values from TextToSpeech

public abstract void error ()

Added in API level 14

The service should call this method if the speech synthesis fails. This method should only be called on the synthesis thread, while in onSynthesizeText(SynthesisRequest, SynthesisCallback).

public abstract int getMaxBufferSize ()

Added in API level 14

Returns
int the maximum number of bytes that the TTS engine can pass in a single call of audioAvailable(byte[], int, int). Calls to audioAvailable(byte[], int, int) with data lengths larger than this value will not succeed.

public abstract boolean hasFinished ()

Added in API level 21

Check if done() was called or not. This method should only be called on the synthesis thread, while in onSynthesizeText(SynthesisRequest, SynthesisCallback). Useful for checking if a fallback from network request is possible.

Returns
boolean

public abstract boolean hasStarted ()

Added in API level 21

Check if start(int, int, int) was called or not. This method should only be called on the synthesis thread, while in onSynthesizeText(SynthesisRequest, SynthesisCallback). Useful for checking if a fallback from network request is possible.

Returns
boolean

public abstract int start (int sampleRateInHz, int audioFormat, int channelCount)

Added in API level 14

The service should call this when it starts to synthesize audio for this request. This method should only be called on the synthesis thread, while in onSynthesizeText(SynthesisRequest, SynthesisCallback).

Parameters
sampleRateInHz Sample rate in HZ of the generated audio.
audioFormat Audio format of the generated audio. Must be one of the ENCODING_ constants defined in AudioFormat.
channelCount The number of channels. Must be 1 or 2.
Returns
int SUCCESS, ERROR or STOPPED.