java调节音量

今天需要给mp3播放器添加音量调节功能.搜索了下,发现了以下方法,大同小异:

 

首先是 Java and Sound, Part 1 中 Playing Sounds with javax.sound提供了一个例子,贴在下面

import java.io.*;

/**
 * This class is a Swing component that can load and play a sound clip,
 * displaying progress and controls. The main( ) method is a test program. This
 * component can play sampled audio or MIDI files, but handles them differently.
 * For sampled audio, time is reported in microseconds, tracked in milliseconds
 * and displayed in seconds and tenths of seconds. For midi files time is
 * reported, tracked, and displayed in MIDI "ticks". This program does no
 * transcoding, so it can only play sound files that use the PCM encoding.
 */
public class SoundPlayer extends JComponent {
	boolean midi; // Are we playing a midi file or a sampled one?
	Sequence sequence; // The contents of a MIDI file
	Sequencer sequencer; // We play MIDI Sequences with a Sequencer
	Clip clip; // Contents of a sampled audio file
	boolean playing = false; // whether the sound is currently playing

	// Length and position of the sound are measured in milliseconds for
	// sampled sounds and MIDI "ticks" for MIDI sounds
	int audioLength; // Length of the sound.
	int audioPosition = 0; // Current position within the sound

	// The following fields are for the GUI
	JButton play; // The Play/Stop button
	JSlider progress; // Shows and sets current position in sound
	JLabel time; // Displays audioPosition as a number
	Timer timer; // Updates slider every 100 milliseconds

	// The main method just creates a SoundPlayer in a Frame and displays it
	public static void main(String[] args) throws IOException,
			UnsupportedAudioFileException, LineUnavailableException,
			MidiUnavailableException, InvalidMidiDataException {
		SoundPlayer player;

		File file = new File("F:\\music\\Dragon Dance.wav"); // This is the file we'll be playing
		// Determine whether it is midi or sampled audio
		boolean ismidi;
		try {
			// We discard the return value of this method; we just need to know
			// whether it returns successfully or throws an exception
			MidiSystem.getMidiFileFormat(file);
			ismidi = true;
		} catch (InvalidMidiDataException e) {
			ismidi = false;
		}

		// Create a SoundPlayer object to play the sound.
		player = new SoundPlayer(file, ismidi);

		// Put it in a window and play it
		JFrame f = new JFrame("SoundPlayer");
		f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		f.getContentPane().add(player, "Center");
		f.pack();
		f.setVisible(true);
	}

	// Create a SoundPlayer component for the specified file.
	public SoundPlayer(File f, boolean isMidi) throws IOException,
			UnsupportedAudioFileException, LineUnavailableException,
			MidiUnavailableException, InvalidMidiDataException {
		if (isMidi) { // The file is a MIDI file
			midi = true;
			// First, get a Sequencer to play sequences of MIDI events
			// That is, to send events to a Synthesizer at the right time.
			sequencer = MidiSystem.getSequencer(); // Used to play sequences
			sequencer.open(); // Turn it on.

			// Get a Synthesizer for the Sequencer to send notes to
			Synthesizer synth = MidiSystem.getSynthesizer();
			synth.open(); // acquire whatever resources it needs

			// The Sequencer obtained above may be connected to a Synthesizer
			// by default, or it may not. Therefore, we explicitly connect it.
			Transmitter transmitter = sequencer.getTransmitter();
			Receiver receiver = synth.getReceiver();
			transmitter.setReceiver(receiver);

			// Read the sequence from the file and tell the sequencer about it
			sequence = MidiSystem.getSequence(f);
			sequencer.setSequence(sequence);
			audioLength = (int) sequence.getTickLength(); // Get sequence length
		} else { // The file is sampled audio
			midi = false;
			// Getting a Clip object for a file of sampled audio data is kind
			// of cumbersome. The following lines do what we need.
			AudioInputStream ain = AudioSystem.getAudioInputStream(f);
			try {
				DataLine.Info info = new DataLine.Info(Clip.class, ain
						.getFormat());
				clip = (Clip) AudioSystem.getLine(info);
				clip.open(ain);
			} finally { // We're done with the input stream.
				ain.close();
			}
			// Get the clip length in microseconds and convert to milliseconds
			audioLength = (int) (clip.getMicrosecondLength() / 1000);
		}

		// Now create the basic GUI
		play = new JButton("Play"); // Play/stop button
		progress = new JSlider(0, audioLength, 0); // Shows position in sound
		time = new JLabel("0"); // Shows position as a #

		// When clicked, start or stop playing the sound
		play.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				if (playing)
					stop();
				else
					play();
			}
		});

		// Whenever the slider value changes, first update the time label.
		// Next, if we're not already at the new position, skip to it.
		progress.addChangeListener(new ChangeListener() {
			public void stateChanged(ChangeEvent e) {
				int value = progress.getValue();
				// Update the time label
				if (midi)
					time.setText(value + "");
				else
					time.setText(value / 1000 + "." + (value % 1000) / 100);
				// If we're not already there, skip there.
				if (value != audioPosition)
					skip(value);
			}
		});

		// This timer calls the tick( ) method 10 times a second to keep
		// our slider in sync with the music.
		timer = new javax.swing.Timer(100, new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				tick();
			}
		});

		// put those controls in a row
		Box row = Box.createHorizontalBox();
		row.add(play);
		row.add(progress);
		row.add(time);

		// And add them to this component.
		setLayout(new BoxLayout(this, BoxLayout.Y_AXIS));
		this.add(row);

		// Now add additional controls based on the type of the sound
		if (midi)
			addMidiControls();
		else
			addSampledControls();
	}

	/** Start playing the sound at the current position */
	public void play() {
		if (midi)
			sequencer.start();
		else
			clip.start();
		timer.start();
		play.setText("Stop");
		playing = true;
	}

	/** Stop playing the sound, but retain the current position */
	public void stop() {
		timer.stop();
		if (midi)
			sequencer.stop();
		else
			clip.stop();
		play.setText("Play");
		playing = false;
	}

	/** Stop playing the sound and reset the position to 0 */
	public void reset() {
		stop();
		if (midi)
			sequencer.setTickPosition(0);
		else
			clip.setMicrosecondPosition(0);
		audioPosition = 0;
		progress.setValue(0);
	}

	/** Skip to the specified position */
	public void skip(int position) { // Called when user drags the slider
		if (position < 0 || position > audioLength)
			return;
		audioPosition = position;
		if (midi)
			sequencer.setTickPosition(position);
		else
			clip.setMicrosecondPosition(position * 1000);
		progress.setValue(position); // in case skip( ) is called from outside
	}

	/** Return the length of the sound in ms or ticks */
	public int getLength() {
		return audioLength;
	}

	// An internal method that updates the progress bar.
	// The Timer object calls it 10 times a second.
	// If the sound has finished, it resets to the beginning
	void tick() {
		if (midi && sequencer.isRunning()) {
			audioPosition = (int) sequencer.getTickPosition();
			progress.setValue(audioPosition);
		} else if (!midi && clip.isActive()) {
			audioPosition = (int) (clip.getMicrosecondPosition() / 1000);
			progress.setValue(audioPosition);
		} else
			reset();
	}

	// For sampled sounds, add sliders to control volume and balance
	void addSampledControls() {
		try {
			FloatControl gainControl = (FloatControl) clip
					.getControl(FloatControl.Type.MASTER_GAIN);
			if (gainControl != null)
				this.add(createSlider(gainControl));
		} catch (IllegalArgumentException e) {
			// If MASTER_GAIN volume control is unsupported, just skip it
		}

		try {
			// FloatControl.Type.BALANCE is probably the correct control to
			// use here, but it doesn't work for me, so I use PAN instead.
			FloatControl panControl = (FloatControl) clip
					.getControl(FloatControl.Type.PAN);
			if (panControl != null)
				this.add(createSlider(panControl));
		} catch (IllegalArgumentException e) {
		}
	}

	// Return a JSlider component to manipulate the supplied FloatControl
	// for sampled audio.
	JSlider createSlider(final FloatControl c) {
		if (c == null)
			return null;
		final JSlider s = new JSlider(0, 1000);
		final float min = c.getMinimum();
		final float max = c.getMaximum();
		final float width = max - min;
		float fval = c.getValue();
		s.setValue((int) ((fval - min) / width * 1000));

		java.util.Hashtable labels = new java.util.Hashtable(3);
		labels.put(new Integer(0), new JLabel(c.getMinLabel()));
		labels.put(new Integer(500), new JLabel(c.getMidLabel()));
		labels.put(new Integer(1000), new JLabel(c.getMaxLabel()));
		s.setLabelTable(labels);
		s.setPaintLabels(true);

		s.setBorder(new TitledBorder(c.getType().toString() + " "
				+ c.getUnits()));

		s.addChangeListener(new ChangeListener() {
			public void stateChanged(ChangeEvent e) {
				int i = s.getValue();
				float f = min + (i * width / 1000.0f);
				c.setValue(f);
			}
		});
		return s;
	}

	// For Midi files, create a JSlider to control the tempo,
	// and create JCheckBoxes to mute or solo each MIDI track.
	void addMidiControls() {
		// Add a slider to control the tempo
		final JSlider tempo = new JSlider(50, 200);
		tempo.setValue((int) (sequencer.getTempoFactor() * 100));
		tempo.setBorder(new TitledBorder("Tempo Adjustment (%)"));
		java.util.Hashtable labels = new java.util.Hashtable();
		labels.put(new Integer(50), new JLabel("50%"));
		labels.put(new Integer(100), new JLabel("100%"));
		labels.put(new Integer(200), new JLabel("200%"));
		tempo.setLabelTable(labels);
		tempo.setPaintLabels(true);
		// The event listener actually changes the tempo
		tempo.addChangeListener(new ChangeListener() {
			public void stateChanged(ChangeEvent e) {
				sequencer.setTempoFactor(tempo.getValue() / 100.0f);
			}
		});

		this.add(tempo);

		// Create rows of solo and checkboxes for each track
		Track[] tracks = sequence.getTracks();
		for (int i = 0; i < tracks.length; i++) {
			final int tracknum = i;
			// Two checkboxes per track
			final JCheckBox solo = new JCheckBox("solo");
			final JCheckBox mute = new JCheckBox("mute");
			// The listeners solo or mute the track
			solo.addActionListener(new ActionListener() {
				public void actionPerformed(ActionEvent e) {
					sequencer.setTrackSolo(tracknum, solo.isSelected());
				}
			});
			mute.addActionListener(new ActionListener() {
				public void actionPerformed(ActionEvent e) {
					sequencer.setTrackMute(tracknum, mute.isSelected());
				}
			});

			// Build up a row
			Box box = Box.createHorizontalBox();
			box.add(new JLabel("Track " + tracknum));
			box.add(Box.createHorizontalStrut(10));
			box.add(solo);
			box.add(Box.createHorizontalStrut(10));
			box.add(mute);
			box.add(Box.createHorizontalGlue());
			// And add it to this component
			this.add(box);
		}
	}
}

 接着在sun论坛上也发现了一个方法:

Java Sound - how to adjust volume level 代码如下:

AudioInputStream ain=AudioSystem.getAudioInputStream(new File(fname));        
        //fname - string
        cont=new byte[8];
        DataLine.Info info = new DataLine.Info(SourceDataLine.class,ain.getFormat());
        /*
         * built-in inner class, constructs the properties information about
         * the given file stream 
         */
        sline=(SourceDataLine)AudioSystem.getLine(info);
        // gets the source line for given audio file using its properties
        sline.open();                
        FloatControl volctrl=(FloatControl)sline.getControl(FloatControl.Type.MASTER_GAIN); 
volctrl.setValue(newVal);// newVal - the value of volume slider

 也就是说,必须开始播放,得到了播放的DataLine以后才可以得到Control信息.

我这么做了,的到

Master Gain with current value: 0.0 dB (range: -80.0 - 6.0206)

不太懂dB是怎么算的,反正默认值为0,也就是说,向正(增大音量)只能移动6个单位.对于一个JSlider来说,实在太小距离了.

不知道怎样让正负可以均匀分布,难道要判断正负,然后正的需要增大10倍来计算?