17.5 Streaming Sounds with javax.sound

Sound files, especially sampled audio files in the uncompressed PCM format, are quite large, and, except for the shortest audio clips, it is not generally a good idea to read the entire file into memory. Instead, these files are typically played in streaming mode so that only the portion of the sound that is currently playing must reside in memory. In exchange for reduced memory consumption, we lose the ability to easily jump to any position within the sound, of course. Example 17-4 is a listing of PlaySoundStream, a program that plays streaming audio data read from the specified URL. It demonstrates streaming techniques for both sampled audio and MIDI data, and also demonstrates a transcoding technique for converting unsupported encodings (such as ALAW and ULAW) into PCM encoding so they can be played. PlaySoundStream is a console-based application with no GUI. Note the use of the wait( ) and notify( ) methods to make streamMidiSequence( ) into a modal method that does not return until the sound has finished playing. Note also that you must use a -m command-line argument in order to play MIDI data.

Example 17-4. PlaySoundStream.java

package je3.sound; import java.io.*; import java.net.*; import javax.sound.sampled.*; import javax.sound.midi.*; /**  * This class plays sounds streaming from a URL: it does not have to preload  * the entire sound into memory before playing it. It is a command-line  * application with no gui. It includes code to convert ULAW and ALAW  * audio formats to PCM so they can be played. Use the -m command-line option  * before MIDI files.  */ public class PlaySoundStream {     // Create a URL from the command-line argument and pass it to the      // right static method depending on the presence of the -m (MIDI) option.     public static void main(String[  ] args) throws Exception {         if (args[0].equals("-m")) streamMidiSequence(new URL(args[1]));         else streamSampledAudio(new URL(args[0]));         // Exit explicitly.         // This is needed because the audio system starts background threads.         System.exit(0);     }     /** Read sampled audio data from the specified URL and play it */     public static void streamSampledAudio(URL url)         throws IOException, UnsupportedAudioFileException,                LineUnavailableException     {         AudioInputStream ain = null;  // We read audio data from here         SourceDataLine line = null;   // And write it here.         try {             // Get an audio input stream from the URL             ain=AudioSystem.getAudioInputStream(url);             // Get information about the format of the stream             AudioFormat format = ain.getFormat( );             DataLine.Info info=new DataLine.Info(SourceDataLine.class,format);             // If the format is not supported directly (i.e. if it is not PCM             // encoded), then try to transcode it to PCM.             if (!AudioSystem.isLineSupported(info)) {                 // This is the PCM format we want to transcode to.                 // The parameters here are audio format details that you                 // shouldn't need to understand for casual use.                 AudioFormat pcm =                     new AudioFormat(format.getSampleRate( ), 16,                                     format.getChannels( ), true, false);                 // Get a wrapper stream around the input stream that does the                 // transcoding for us.                 ain = AudioSystem.getAudioInputStream(pcm, ain);                 // Update the format and info variables for the transcoded data                 format = ain.getFormat( );                  info = new DataLine.Info(SourceDataLine.class, format);             }             // Open the line through which we'll play the streaming audio.             line = (SourceDataLine) AudioSystem.getLine(info);             line.open(format);               // Allocate a buffer for reading from the input stream and writing             // to the line.  Make it large enough to hold 4k audio frames.             // Note that the SourceDataLine also has its own internal buffer.             int framesize = format.getFrameSize( );             byte[  ] buffer = new byte[4 * 1024 * framesize]; // the buffer             int numbytes = 0;                               // how many bytes             // We haven't started the line yet.             boolean started = false;             for(;;) {  // We'll exit the loop when we reach the end of stream                 // First, read some bytes from the input stream.                 int bytesread=ain.read(buffer,numbytes,buffer.length-numbytes);                 // If there were no more bytes to read, we're done.                 if (bytesread == -1) break;                 numbytes += bytesread;                                  // Now that we've got some audio data to write to the line,                 // start the line, so it will play that data as we write it.                 if (!started) {                     line.start( );                     started = true;                 }                                  // We must write bytes to the line in an integer multiple of                 // the framesize.  So figure out how many bytes we'll write.                 int bytestowrite = (numbytes/framesize)*framesize;                                  // Now write the bytes. The line will buffer them and play                 // them. This call will block until all bytes are written.                 line.write(buffer, 0, bytestowrite);                                  // If we didn't have an integer multiple of the frame size,                  // then copy the remaining bytes to the start of the buffer.                 int remaining = numbytes - bytestowrite;                 if (remaining > 0)                     System.arraycopy(buffer,bytestowrite,buffer,0,remaining);                 numbytes = remaining;             }             // Now block until all buffered sound finishes playing.             line.drain( );         }         finally { // Always relinquish the resources we use             if (line != null) line.close( );             if (ain != null) ain.close( );         }     }     // A MIDI protocol constant that isn't defined by javax.sound.midi     public static final int END_OF_TRACK = 47;     /* MIDI or RMF data from the specified URL and play it */     public static void streamMidiSequence(URL url)         throws IOException, InvalidMidiDataException, MidiUnavailableException     {         Sequencer sequencer=null;     // Converts a Sequence to MIDI events         Synthesizer synthesizer=null; // Plays notes in response to MIDI events         try {             // Create, open, and connect a Sequencer and Synthesizer             // They are closed in the finally block at the end of this method.             sequencer = MidiSystem.getSequencer( );             sequencer.open( );               synthesizer = MidiSystem.getSynthesizer( );             synthesizer.open( );             sequencer.getTransmitter( ).setReceiver(synthesizer.getReceiver( ));             // Specify the InputStream to stream the sequence from             sequencer.setSequence(url.openStream( ));                            // This is an arbitrary object used with wait and notify to              // prevent the method from returning before the music finishes             final Object lock = new Object( );             // Register a listener to make the method exit when the stream is              // done. See Object.wait( ) and Object.notify( )             sequencer.addMetaEventListener(new MetaEventListener( ) {                     public void meta(MetaMessage e) {                         if (e.getType( ) == END_OF_TRACK) {                             synchronized(lock) {                                  lock.notify( );                             }                         }                     }                 });                          // Start playing the music             sequencer.start( );                          // Now block until the listener above notifies us that we're done.             synchronized(lock) {                 while(sequencer.isRunning( )) {                     try { lock.wait( ); } catch(InterruptedException e) {  }                 }             }         }         finally {             // Always relinquish the sequencer, so others can use it.             if (sequencer != null) sequencer.close( );             if (synthesizer != null) synthesizer.close( );         }     } }