Clip.start() behaviour

[Arka Sharma]

Hi,

I have written a very simple code to play .wav files using Java sound api.My question is this that why do I need to put Thread.sleep() to halt the execution after calling clip.start() method.The behaviour of startn is not clear to me actually.I have seen java docs for Clip as well as Sun's doc for Sound API.

Regards,
Arka

[Rob Spoor]

You shouldn't need Thread.sleep at all. Can you show us the code that creates and starts the clip?

[Arka Sharma]

This is what I'm doing

package soundpackage;

import java.io.File;
import java.io.IOException;

import javax.sound.sampled.AudioFormat;
import javax.sound.sampled.AudioInputStream;
import javax.sound.sampled.AudioSystem;
import javax.sound.sampled.Clip;
import javax.sound.sampled.DataLine;
import javax.sound.sampled.LineUnavailableException;
import javax.sound.sampled.Port;

public class Clips {

	
	public static void main(String[] args) {
		if(args.length!=1)
		{
			System.out.println("Please enter the name of the file");
			return;
		}
		File soundFile = new File(args[0]);
		AudioFormat format = null;
		AudioInputStream inputStream = null;
		Port speakerPort = null;
		Clip clip = null;
		try
		{
			inputStream = AudioSystem.getAudioInputStream(soundFile);
			format = inputStream.getFormat();
			speakerPort = (Port) AudioSystem.getLine(Port.Info.SPEAKER);
		}catch (Exception e) {
			System.out.println("Exception");
		}
		try
		{
			DataLine.Info clipInfo = new DataLine.Info(Clip.class,format);
			clip = (Clip) AudioSystem.getLine(clipInfo);
		}catch (Exception e) {
			System.out.println("Exception");
		}
		
		try {
			clip.open(inputStream);
			/*System.out.println("Frame Length : "+clip.getFrameLength());
			System.out.println("Dutration in Seconds : "+clip.getMicrosecondLength()/Math.pow(10, 6));
			//System.out.println(clip.getFramePosition());
			clip.start();*/
			System.out.println("Frame Length : "+clip.getFrameLength());
			for(int i=0;i<5;i++){
				clip.start();
				
				Thread.sleep(1000);
				clip.setFramePosition(0);
			}
		} catch (LineUnavailableException e) {
			System.out.println("Line Unavailable");
		} catch (IOException e) {
			System.out.println("IO Exception");
		}
		catch (InterruptedException e) {
			System.out.println("Interrupted Exception");
		}
		
	}

}

[Rob Spoor]

Apparently calling start will create a daemon thread for playing the clip in the background without blocking until it's ready, and this daemon thread does not cause the JVM to stay alive. Therefore, when your main method ends, so does the clip. Also, when the loop hits the next iteration, the clip is overwritten, causing the existing clip to stop.

If you need to play music files and block until they are done, you should use either JMF or a third party library. JMF is event based so you'd need to write your own method to wait for the end. A quick approach:

// player is a javax.media.Player that's all ready for playing (i.e. it's realized and all)
final CountDownLatch latch = new CountDownLatch(1);
player.addControllerListener(new ControllerListener()
{
    public void controllerUpdate(ControllerEvent event)
    {
        if (event instanceof StopEvent) // for any kind of stop, otherwise EndOfMediaEvent for only "finished playing"
        {
            latch.countDown();
        }
    }
});
player.start();
latch.await(); // wait until the controller listener counts down the latch to 0
// so here either a StopEvent or an EndOfMediaEvent occurred.