QuickTime for Java: A Developer's Notebook

Preventing “Tasking” Problems

All the tasks in this chapter have managed to avoid one of the more obscure hazards in QuickTime. This example tempts fate and exposes the problem by playing a movie that would otherwise freeze up.

How do I do that?

Example 2-7 reprises the command-line audio player from the first chapter, which takes a path to a file as a command-line argument, builds a Movie, and plays it, without getting any kind of GUI.

Example 2-7. Playing audio from the command line

package com.oreilly.qtjnotebook.ch01;
 
import quicktime.*;
import quicktime.app.time.*;
import quicktime.io.*;
import quicktime.std.*;
import quicktime.std.movies.*;
 
import java.io.*;
 
public class BasicAudioPlayer {
 
  public static void main (String[  ] args) {
      if (args.length != 1) {
          System.out.println (
              "Usage: BasicAudioPlayer <file>");
          return;
      }
      try {
          QTSessionCheck.check( );
          QTFile f = new QTFile (new File(args[0]));
          OpenMovieFile omf = OpenMovieFile.asRead(f);
          Movie movie = Movie.fromFile (omf);
          TaskAllMovies.addMovieAndStart( );
          movie.start( );
      } catch (QTException e) {
          e.printStackTrace( );
      }
  }
}

Notice the line in bold. Take it out, recompile, and watch what happens. The program will likely hang or immediately exit, playing just a spurt of audio or none at all.

What just happened?

QuickTime movies need to explicitly be given CPU time to do their work: reading from disk or the network, decompressing and decoding, rendering to the screen, or playing to the speakers. This process is called “tasking.” ...