CODEWITHSUNDEEP
androidaudio
Matt
Matt

Reputation: 2680

Looping an audio file

I'm trying to generate and play a square wave. I'm generating the signal and then using

track = new AudioTrack(AudioManager.STREAM_MUSIC,
                sampleRate, AudioFormat.CHANNEL_CONFIGURATION_MONO,
                AudioFormat.ENCODING_PCM_16BIT, minSize,
                AudioTrack.MODE_STREAM);    
track.write(signal, 0, signal.length);

and then calling track.play(). The problem is it only plays once. It looks like there is a method to set the loop points, but I don't know what to put in for the frames.

I have also tried calling track.write() and then track.play() in a while loop, but there is a short lag, and I don't think this is the correct way anyway.

What IS the correct way to have a seamless loop?

Upvotes: 2

Views: 5375

Answers (4)

Gerry
Gerry

Reputation: 86

I faced the same problem now and seems loop doesn't work well for me, there is always a little "break" between loop, then I try to continue generate sound and feed the audiotrack, it works for me:

class ToneGenerator {
    int sampleRate = 8000;
    double sample[] = null;
    byte generatedSnd[] = null;
    int m_ifreq = 400;
    Thread m_PlayThread = null;
    boolean m_bStop = false;
    AudioTrack m_audioTrack = null;
    int m_play_length = 1000;//in seconds

    static public void PlayTone(int freq, int play_length) {
        ToneGenerator player = new ToneGenerator();
        player.m_ifreq = freq;
        player.m_play_length = play_length;
        player.play();
    }

    synchronized void stop() {
        m_bStop = true;
        if (m_PlayThread != null) {
            try {
                m_PlayThread.interrupt();
                m_PlayThread.join();
                m_PlayThread = null;
            } catch (Exception e) {

            }
        }
        if (m_audioTrack != null) {
            m_audioTrack.stop();
            m_audioTrack.release();
            m_audioTrack = null;
        }
    }

    synchronized void play() {
        m_bStop = false;
        m_PlayThread = new Thread() {
            public void run() {
                try {
                    int iToneStep = 0;

                    m_audioTrack = new AudioTrack(AudioManager.STREAM_MUSIC,
                            sampleRate, AudioFormat.CHANNEL_OUT_MONO,
                            AudioFormat.ENCODING_PCM_16BIT, 2 * sampleRate,
                            AudioTrack.MODE_STREAM);

                    while (!m_bStop && m_play_length-- > 0) {
                        genTone(iToneStep++);

                        m_audioTrack.write(generatedSnd, 0, generatedSnd.length);
                        if (iToneStep == 1) {
                            m_audioTrack.play();
                        }
                    }
                } catch (Exception e) {
                    Log.e("Tone", e.toString());
                } catch (OutOfMemoryError e) {
                    Log.e("Tone", e.toString());
                }

            }
        };
        m_PlayThread.start();
    }

    //Generate tone data for 1 seconds
    synchronized void genTone(int iStep) {
        sample = new double[sampleRate];

        for (int i = 0; i < sampleRate; ++i) {
            sample[i] = Math.sin(2 * Math.PI * (i + iStep * sampleRate) / (sampleRate / m_ifreq));
        }

        // convert to 16 bit pcm sound array
        // assumes the sample buffer is normalised.
        generatedSnd = new byte[2 * sampleRate];
        int idx = 0;
        for (final double dVal : sample) {
            // scale to maximum amplitude
            final short val = (short) ((dVal * 32767));
            // in 16 bit wav PCM, first byte is the low order byte
            generatedSnd[idx++] = (byte) (val & 0x00ff);
            generatedSnd[idx++] = (byte) ((val & 0xff00) >>> 8);
        }
    }

}

Upvotes: 0

R Earle Harris
R Earle Harris

Reputation: 983

To loop in MODE_STREAM, wait until your write loop is finished. Then set loop points, then call play again. Nothing I have done with looping, or even non-looping AudioTrack, has cured the click on start.

Upvotes: 1

Hemant Mendi Ratta
Hemant Mendi Ratta

Reputation: 129

To loop the audio file infinite times set loop to -1. To remove a delay while looping an audio file use the SoundPool class instead of MediaPlayer.

Upvotes: 0

Femi
Femi

Reputation: 64700

There's a very similar question: https://stackoverflow.com/questions/4241724/androidaudiotrack-setlooppoint-issue

If I read the Android docs correctly, you are using 16-bit samples, so the signal.length/2 is the number of samples. I'd try:

track.setLoopPoints(0, signal.length/2, -1);

Upvotes: 6

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