How to play fragments of mp3 with JavaFX? - javafx-2

Question

I want to develop a Java program playing an mp3-file in a specific manner. I marked a number of fragments in this file with startTime and endTime. The program should play the first fragment and then sleep for 5 seconds. Then play the second fragment and sleep again. And so on. I use JavaFX class MediaPlayer. The program prototype is as follows:
import javafx.application.Application;
import javafx.stage.Stage;
import java.io.FileNotFoundException;
import java.io.IOException;
import javafx.scene.media.Media;
import javafx.scene.media.MediaPlayer;
import javafx.util.Duration;
import java.util.concurrent.TimeUnit;
public class JavaFXMediaPlayer02 extends Application {
#Override
public void start(Stage stage) throws FileNotFoundException,IOException,InterruptedException {
Media media = new Media("file:///D:/1016_00.mp3");
MediaPlayer mediaPlayer = new MediaPlayer(media);
//Set and play the first fragment of mp3-file
mediaPlayer.setStartTime(Duration.millis(1219.0));
mediaPlayer.setStopTime(Duration.millis(2728.0));
mediaPlayer.play();
System.out.println("1st fragment played!");
TimeUnit.SECONDS.sleep(5);
//Set and play the second fragment
mediaPlayer.setStartTime(Duration.millis(3947.0));
mediaPlayer.setStopTime(Duration.millis(6629.0));
mediaPlayer.play();
System.out.println("2nd fragment played!");
TimeUnit.SECONDS.sleep(5);
//Set and play the second fragment
mediaPlayer.setStartTime(Duration.millis(7453.0));
mediaPlayer.setStopTime(Duration.millis(10704.0));
mediaPlayer.play();
System.out.println("3rd fragment played!");
}
public static void main(String[] args) {
launch(args);
}
}
But I only hear the 3rd fragment. What's the matter? Why don't I hear the first and the second fragments? How to correct my program? Isn't JavaFX an appropriate tool for my task?

Answer 1

The problem here lies in the TimeUnit.SECONDS.sleep(5); invokation. This method sets the current thread into sleep. And in your case this thread is the JavaFX Application Thread. That causes the whole application to "freeze" (which would be more obviously if you added some GUI-Elements) and therefore the mediaPlayer.play(); commands are executed, but are instantly "freezed" because of the sleep function. After the `TimeUnit.SECONDS.sleep(5); calls, you set new start and end times for your MediaPlayer and execute play() again, so that the track starts at the new start time. Thats why only your last fragment is played.
Now to the solution:
You should never invoke Thread.sleep() or similar methods on the JavaFX App Thread. But in your case you have to wait a certain amount of time between playing the fragments. The first approach would be invoke Thread.sleep() or TimeUnit.SECONDS.sleep(5); on a new thread and call the Mediaplayer methods on the JFX App Thread. But that doesn't work properly because you haven't set up an "order" in which the threads are called. There are various ways to do this (via Semaphores, Locks and Conditions, JavaFX Concurrency and so on...)
I tried to solve your problem by doing some quick-and-dirty programming, but i came across a problem with mediaPlayer.setStopTime(Duration.millis());. It does not seem to work on my computers, so that the files are always played to the end. I added a stop button to simulate the automatic stopping.
The following class sets the new start and endpoints and plays the fragment. If the mediaplayer is stops, it calls the next fragment on the LittleMediaScheduler class.
public class LittleMediaHelper implements Runnable {
public double startTime;
public double endTime;
public MediaPlayer player;
public int id;
public LittleMediaScheduler scheduler;
public LittleMediaHelper(double startTime, double endTime,
MediaPlayer player, int id) {
this.startTime = startTime;
this.endTime = endTime;
this.player = player;
this.id = id;
}
public LittleMediaScheduler getScheduler() {
return scheduler;
}
public void setScheduler(LittleMediaScheduler scheduler) {
this.scheduler = scheduler;
}
#Override
public void run() {
Platform.runLater(new Runnable() {
#Override
public void run() {
player.setStartTime(Duration.millis(startTime));
player.setStopTime(Duration.millis(endTime));
System.out.println(player.getStartTime());
System.out.println(player.getStopTime());
player.play();
player.setOnStopped(new Runnable() {
#Override
public void run() {
int idtmp = id + 1;
System.out.println("NEXT " + idtmp);
scheduler.call(idtmp);
}
});
}
});
}
}
This class is responsibly for sleeping a certain amount on a new thread and after successfully sleeping invoking the next LittleMediaHelper class play functionality.
public class LittleMediaScheduler {
private ArrayList<LittleMediaHelper> hArrL;
private int SLEEPTIME = 2000;
public LittleMediaScheduler(LittleMediaHelper... helpers) {
this.hArrL = new ArrayList<>();
for (LittleMediaHelper h : helpers) {
h.setScheduler(this);
System.out.println(h.startTime);
this.hArrL.add(h);
}
System.out.println(hArrL.size());
}
public void init() {
Thread t = new Thread(this.hArrL.get(0));
t.start();
}
public void call(final int id) {
Thread t = new Thread(new Task<String>() {
#Override
protected String call() throws Exception {
Thread.sleep(SLEEPTIME);
return null;
}
#Override
protected void succeeded() {
super.succeeded();
System.out.println("Next playing...");
if (id > LittleMediaScheduler.this.hArrL.size() - 1) {
return;
}
LittleMediaHelper next = LittleMediaScheduler.this.hArrL
.get(id);
Thread nextT = new Thread(next);
nextT.start();
}
});
t.start();
}
}
The main class with a stop button. Without mediaPlayer.pause() the player somehow repeats one step twice although new start end endpoints are set. Don't know if this is a bug or not.
public class JavaFXMediaPlayer02 extends Application {
#Override
public void start(Stage stage) throws FileNotFoundException, IOException,
InterruptedException {
Media media = new Media("file:///C:/test.mp3");
final MediaPlayer mediaPlayer = new MediaPlayer(media);
LittleMediaHelper phase1 = new LittleMediaHelper(0, 1000, mediaPlayer,
0);
LittleMediaHelper phase2 = new LittleMediaHelper(50000, 55000,
mediaPlayer, 1);
LittleMediaHelper phase3 = new LittleMediaHelper(200000, 200500,
mediaPlayer, 2);
LittleMediaScheduler scheduler = new LittleMediaScheduler(phase1,
phase2, phase3);
scheduler.init();
Group g = new Group();
Button b = new Button("STOP");
b.setOnAction(new EventHandler<ActionEvent>() {
#Override
public void handle(ActionEvent arg0) {
mediaPlayer.pause();
mediaPlayer.stop();
}
});
g.getChildren().add(b);
Scene sc = new Scene(g);
stage.setScene(sc);
stage.show();
}
public static void main(String[] args) {
launch(args);
}
}