core/java/android/speech/tts/SynthesisCallback.java

/*
 * Copyright (C) 2011 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */
package android.speech.tts;

/**
 * A callback to return speech data synthesized by a text to speech engine.
 *
 * The engine can provide streaming audio by calling
 * {@link #start}, then {@link #audioAvailable} until all audio has been provided, then finally
 * {@link #done}.
 *
 * {@link #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 {@link #done}, it might be discarded.
 *
 * After {@link #start} been called, {@link #done} must be called regardless of errors.
 */
public interface SynthesisCallback {
    /**
     * @return the maximum number of bytes that the TTS engine can pass in a single call of
     *         {@link #audioAvailable}. Calls to {@link #audioAvailable} with data lengths
     *         larger than this value will not succeed.
     */
    public int getMaxBufferSize();

    /**
     * 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 {@link TextToSpeechService#onSynthesizeText}.
     *
     * @param sampleRateInHz Sample rate in HZ of the generated audio.
     * @param audioFormat Audio format of the generated audio. Must be one of
     *         the ENCODING_ constants defined in {@link android.media.AudioFormat}.
     * @param channelCount The number of channels. Must be {@code 1} or {@code 2}.
     * @return {@link TextToSpeech#SUCCESS} or {@link TextToSpeech#ERROR}.
     */
    public int start(int sampleRateInHz, int audioFormat, int channelCount);

    /**
     * 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 {@link TextToSpeechService#onSynthesizeText}.
     *
     * @param buffer The generated audio data. This method will not hold on to {@code buffer},
     *         so the caller is free to modify it after this method returns.
     * @param offset The offset into {@code buffer} where the audio data starts.
     * @param length The number of bytes of audio data in {@code buffer}. This must be
     *         less than or equal to the return value of {@link #getMaxBufferSize}.
     * @return {@link TextToSpeech#SUCCESS} or {@link TextToSpeech#ERROR}.
     */
    public int audioAvailable(byte[] buffer, int offset, int length);

    /**
     * The service should call this method when all the synthesized audio for a request has
     * been passed to {@link #audioAvailable}.
     *
     * This method should only be called on the synthesis thread,
     * while in {@link TextToSpeechService#onSynthesizeText}.
     *
     * This method has to be called if {@link #start} was called.
     *
     * @return {@link TextToSpeech#SUCCESS} or {@link TextToSpeech#ERROR}.
     */
    public int done();

    /**
     * The service should call this method if the speech synthesis fails.
     *
     * This method should only be called on the synthesis thread,
     * while in {@link TextToSpeechService#onSynthesizeText}.
     */
    public void error();

}