Android Open Source - speech_trainer Player

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License

The source code is released under:
GNU General Public License
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Java Source Code

/**
 * This file is part of Speech Trainer.//from   w w  w. j ava  2  s. c o m
 * Copyright (C) 2011 Jan Wrobel <wrr@mixedbit.org>
 * 
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

package mixedbit.speechtrainer.controller;

import mixedbit.speechtrainer.controller.AudioBufferAllocator.AudioBuffer;
import android.media.AudioTrack;

/**
 * Wrapper over AudioTrack that exposes minimal interface for playing
 * AudioBuffers. Informs AudioEventListener about each executed action (playing
 * started, audio buffer played, playing stopped). The interface is extracted
 * from the PlayerImpl class to allow mocking with the standard EasyMock.
 * EasyMock fails to mock classes that depend on Android classes (AudioTrack in
 * this case).
 */
interface Player {

    /**
     * Starts playing. Calls to writeAudioBuffer are allowed only after playing
     * was started.
     */
    public abstract void startPlaying();

    /**
     * Writes an audio buffer to be played. Requires playing to be started
     * (startPlaying called). Audio data is copied to an output buffer and
     * played asynchronously. Can block if an output buffer is full.
     */
    public abstract void writeAudioBuffer(AudioBuffer audioBuffer);

    /**
     * Stops playing. Playing can be started again with the startPlaying method.
     */
    public abstract void stopPlaying();

}

class PlayerImpl implements Player {
    private final AudioTrack audioTrack;
    private final AudioEventListener audioEventListener;
    // A buffer of silence, used to flush audio data when playing is stopped.
    private final short[] silenceBuffer;

    /**
     * @param audioTrack
     *            AudioTrack object configured by a caller.
     * @param outputBufferSizeInBytes
     *            The size of the output buffer that was passed to the
     *            AudioTrack constructor.
     * @param audioEventListener
     *            Listener that is informed about each action executed by the
     *            player.
     */
    public PlayerImpl(AudioTrack audioTrack, int outputBufferSizeInBytes,
            AudioEventListener audioEventListener) {
        this.audioTrack = audioTrack;
        silenceBuffer = new short[outputBufferSizeInBytes / 2];
        this.audioEventListener = audioEventListener;
    }

    @Override
    public void startPlaying() {
        audioTrack.play();
        this.audioEventListener.playingStarted();
    }

    @Override
    public void writeAudioBuffer(AudioBuffer audioBuffer) {
        if (writeRawBuffer(audioBuffer.getAudioData(), audioBuffer.getAudioDataLengthInShorts())) {
            audioEventListener.audioBufferPlayed(
                    audioBuffer.getAudioBufferId(), audioBuffer.getSoundLevel());
        }
    }

    @Override
    public void stopPlaying() {
        // stopPlaying needs to wait for playing to stop, otherwise when
        // recording is started, audio data can be still played and can be
        // recorded again.
        // Surprisingly, audioTrack.flush() and audioTrack.stop() do not
        // synchronously wait for the playing to stop. Audio hardware finishes
        // playing data that is left in the output buffer and it can do
        // it after flush and stop returned. To be 100% sure that playing has
        // stopped, the whole output buffer is filled with silence. If there
        // is any audio data left in the buffer, filling with silence
        // will blocks, until the data is played.
        writeRawBuffer(silenceBuffer, silenceBuffer.length);
        audioTrack.flush();
        audioTrack.stop();
        this.audioEventListener.playingStopped();
    }

    private boolean writeRawBuffer(short[] buffer, int bufferLength) {
        int totalWrittenAudioDataLength = 0;
        // On all tested devices, write() outputs the whole buffer in a single
        // call. But since the API documentation is not clear about this, the
        // loop handles the case of write() outputting only part of
        // the buffer.
        while (totalWrittenAudioDataLength < bufferLength) {
            final int writtenAudioDataLength = audioTrack.write(buffer,
                    totalWrittenAudioDataLength, bufferLength - totalWrittenAudioDataLength);
            if (writtenAudioDataLength < 0) {
                // Such error should not happen since audioTrack is guaranteed
                // to be properly initialized.
                return false;
            }
            totalWrittenAudioDataLength += writtenAudioDataLength;
        }
        return true;
    }

}
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