Question

i’m programming for Android 2.1.Could you help me with the following problem?

I have three files, and the general purpose is to play a sound with audiotrack buffer by buffer. I’m getting pretty desperate here because I tried about everything, and there still is no sound coming out of my speakers (while android’s integrated mediaplayer has no problem playing sounds via the emulator).

Source code:

An audioplayer class, which implements the audio track. It will receive a buffer, in which the sound is contained.

    public AudioPlayer(int sampleRate, int channelConfiguration, int audioFormat) throws ProjectException {
        minBufferSize = AudioTrack.getMinBufferSize(sampleRate, channelConfiguration, audioFormat);
        audioTrack = new AudioTrack(AudioManager.STREAM_MUSIC, sampleRate, channelConfiguration,
                                    audioFormat, minBufferSize, AudioTrack.MODE_STREAM); 

        if(audioTrack == null)
            throw new ProjectException("Erreur lors de l'instantiation de AudioTrack");

        audioTrack.setStereoVolume((float)1.0, (float)1.0);
    }

    @Override
    public void addToQueue(short[] buffer) {
         audioTrack.write(buffer, 0, buffer.length*Short.SIZE);
         if(!isPlaying ) {
             audioTrack.play();
             isPlaying = true;
         }
    }

A model class, which I use to fill the buffer. Normally, it would load sound from a file, but here it just uses a simulator (440Hz), for debugging.

Buffer sizes are chosen very loosely; normally first buffer size should be 6615 and then 4410. That’s, again, only for debug.

public void onTimeChange() {
    if(begin) {

                    //First fill about 300ms

        begin = false;
        short[][] buffer = new short[channels][numFramesBegin];
                    //numFramesBegin is for example 10000
                    //For debugging only buffer[0] is useful
        fillSimulatedBuffer(buffer, framesRead);
        framesRead += numFramesBegin;
        audioPlayer.addToQueue(buffer[0]);

    }

    else {
        try {
            short[][] buffer = new short[channels][numFrames];

                            //Afterwards fill like 200ms

            fillSimulatedBuffer(buffer, framesRead);
            framesRead += numFrames;
            audioPlayer.addToQueue(buffer[0]);
        } catch (Exception e) {
            e.printStackTrace();
        }


    }
}

private short simulator(int time, short amplitude) {
            //a pure A (frequency=440)
            //this is probably wrong due to sampling rate, but 44 and 4400 won't work either
    return (short)(amplitude*((short)(Math.sin((double)(simulatorFrequency*time)))));
}

private void fillSimulatedBuffer(short[][] buffer, int offset) {
         for(int i = 0; i < buffer[0].length; i++)
        buffer[0][i] = simulator(offset + i, amplitude);
}

A timeTask class that calls model.ontimechange() every 200 ms.

public class ReadMusic extends TimerTask {
private final Model model;

public ReadMusic(Model model) {
    this.model = model;
}


@Override
public void run() {
    System.out.println("Task run");
    model.onTimeChange();
}

}

What debugging showed me:

• timeTask works fine, it does its job;
• Buffer values seem coherent, and buffer size is bigger than minBufSize;
• Audiotrack’s playing state is “playing”
• no exceptions are caught in model functions.

Any ideas would be greatly appreciated!

Answer 1

OK I found the problem.

There is an error in the current AudioTrack documentation regarding AudioTrack and short buffer input: the specified buffer size should be the size of the buffer itself (buffer.length) and not the size in bytes.