A callback to return speech data synthesized by a text to speech engine. The engine can provide streaming audio by calling ISynthesisCallback.Start(int, Android.Media.Encoding, Android.Media.Encoding), then ISynthesisCallback.AudioAvailable(Byte[], System.Int32, System.Int32) until all audio has been provided, then finally ISynthesisCallback.Done. ISynthesisCallback.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 ISynthesisCallback.Done, it might be discarded. ISynthesisCallback.Done must be called at the end of synthesis, regardless of errors. All methods can be only called on the synthesis thread.

[Android Documentation]