Changing volume in Java when using JLayer

问题

I'm using JLayer to play an inputstream of mp3 data from the internet. How do i change the volume of the output?

I'm using this code to play it:

URL u = new URL(s);
URLConnection conn = u.openConnection();  
conn.setConnectTimeout(Searcher.timeoutms);  
conn.setReadTimeout(Searcher.timeoutms);

bitstream = new Bitstream(conn.getInputStream()/*new FileInputStream(quick_file)*/);
System.out.println(bitstream);
decoder = new Decoder();
decoder.setEqualizer(equalizer);
audio = FactoryRegistry.systemRegistry().createAudioDevice();
audio.open(decoder);
for(int i = quick_positions[0]; i > 0; i--){
    Header h = bitstream.readFrame();
    if (h == null){
        return;
    }
bitstream.closeFrame();

回答1:

You may consider this an unacceptable hack, but it worked in an MP3 player I wrote. It requires a small code addition to one of the JLayer classes.

Add the following method to javazoom.jl.player.JavaSoundAudioDevice.

public void setLineGain(float gain)
{
    if (source != null)
    {
        FloatControl volControl = (FloatControl) source.getControl(FloatControl.Type.MASTER_GAIN);
        float newGain = Math.min(Math.max(gain, volControl.getMinimum()), volControl.getMaximum());

        volControl.setValue(newGain);
    }
}

This new method then allows you to change the volume with code like this.

if (audio instanceof JavaSoundAudioDevice)
{
    JavaSoundAudioDevice jsAudio = (JavaSoundAudioDevice) audio;
    jsAudio.setLineGain(yourGainGoesHere);
}

回答2:

Another (non-JLayer) way to adjust the PC's speaker volume is to use classes in the javax.sound.sampled package provided by Sun/Oracle.

On my machine, SPEAKER was the only output target supported.

import javax.sound.sampled.AudioSystem;
import javax.sound.sampled.FloatControl;
import javax.sound.sampled.Line.Info;
import javax.sound.sampled.LineUnavailableException;
import javax.sound.sampled.Port;

public class SoundVolumeDemo 
{

    public static void main(String[] args) 
{        
    Info source = Port.Info.SPEAKER;
    //        source = Port.Info.LINE_OUT;
    //        source = Port.Info.HEADPHONE;

        if (AudioSystem.isLineSupported(source)) 
        {
            try 
            {
                Port outline = (Port) AudioSystem.getLine(source);
                outline.open();                
                FloatControl volumeControl = (FloatControl) outline.getControl(FloatControl.Type.VOLUME);                
                System.out.println("       volume: " + volumeControl.getValue() );
                float v = 0.33F;
                volumeControl.setValue(v);
                System.out.println("   new volume: " + volumeControl.getValue() );
                v = 0.73F;
                volumeControl.setValue(v); 
                System.out.println("newest volume: " + volumeControl.getValue() );
            } 
            catch (LineUnavailableException ex) 
            {
                System.err.println("source not supported");
                ex.printStackTrace();
            }            
        }
    } 

 }

This is how I am achieving volume control in this app:

http://onebeartoe.com/media-players/randomjuke/filesystem/java-web-start/swing/index.jsp

Please note that I have only had experience with it working on MS Windows OS machines.

回答3:

Try adjusting all bands of the equalizer for the volume you’re trying to get. Maybe you can also use an EQFunction for that?

public class ChangeVolumeFunction extends EQFunction {
    public double volume = 1.0;
    public void setVolume(double volume) { this.volume = volume; }
    public float getBand(int band) { return (float) (Math.log(volume) / Math.log(2) * 6.0); }
}

回答4:

I made my own version on ChrisH's answer, but instead of changing the source code of JLayer, I did it via reflection:

Class<JavaSoundAudioDevice> clazz = JavaSoundAudioDevice.class;
Field[] fields = clazz.getDeclaredFields();

try{
    SourceDataLine source = null;
        for(Field field : fields) {
            if("source".equals(field.getName())) {
                field.setAccessible(true);
                source = (SourceDataLine) field.get(device);
                field.setAccessible(false);

                FloatControl volControl = (FloatControl) source.getControl(FloatControl.Type.MASTER_GAIN);
                if (volControl != null) {
                     float newGain = Math.min(Math.max(gain, volControl.getMinimum()), volControl.getMaximum());
                     volControl.setValue(newGain);
                }
            }
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
}

Kinda crude, but it works

来源：https://stackoverflow.com/questions/648107/changing-volume-in-java-when-using-jlayer