Accessing the Android media stream for audio visualization

Question

Basically, I want to make an audio visualizer. I know it\'s possible, because my phone came with a few live wallpapers that do it. The problem is, I can\'t seem to figure

Answer 1

The MusicVisualization wallpaper source is available at the AOSP. It basically seems to involve calling MediaPlayer.snoop(), an undocumented method added in Eclair.

Answer 2

It looks like in 2.3 things have changed here, there is permissions now

<uses-permission android:name="android.permission.RECORD_AUDIO"/>
<uses-permission android:name="android.permission.MODIFY_AUDIO_SETTINGS"/>

And there is a AudioCapture helper class in the aosp to help the live wallpapers do it properly. https://android.googlesource.com/platform/packages/wallpapers/MusicVisualization/+/gingerbread-release/src/com/android/musicvis/AudioCapture.java

Edit:

One of the imports in the AOSP doesn't match the public api.
import android.media.audiofx.Visualizer;

it is
import android.media.Visualizer;

if it gives a headache make sure to switch. This is all 2.3 api, it apparently returns a low-resolution audio stream for viz, but not good enough for recording.

Answer 3

A slightly faster snoop() would be to call Class.getMethod() once, and then to use a custom parseInt() instead of Integer.parseInt()...

private static Method mSnoop;

//..(http://nadeausoftware.com/node/97)..
private static int customParseInt( final String s )
{
    // Check for a sign.
    int num  = 0;
    int sign = -1;
    final int len  = s.length( );
    final char ch  = s.charAt( 0 );
    if ( ch == '-' )
        sign = 1;
    else
        num = '0' - ch;

    // Build the number.
    int i = 1;
    while ( i < len )
        num = num*10 + '0' - s.charAt( i++ );

    return sign * num;
} 

private static int snoop(short [] outData, int kind)
{    
    if ( mSnoop != null )
    {
        try
        {
            return customParseInt( (mSnoop.invoke( MediaPlayer.class , outData, kind)).toString() );
        }
        catch ( Exception e )
        {
            Log.e( TAG, "Failed to MediaPlayer.snoop()!", e );
            return 1;
        }
    }
    else
    {
        try {
            Class c = MediaPlayer.class;
            Method m = c.getMethod("snoop", outData.getClass(), Integer.TYPE);
            m.setAccessible(true);
            mSnoop = m;
            return customParseInt( (m.invoke(c, outData, kind)).toString() ); 
        } 
        catch (Exception e) 
        {
            Log.e( TAG, "Failed to MediaPlayer.snoop()!", e );
            return 1;
        }
    }
}

Answer 4

This is how I did it from my application:

protected short [] mAudioData = new short[1024];

Then in the loop:

int res = snoop(mAudioData, 0);

And here is the function itself:

public static int snoop(short [] outData, int kind){    
    try {
        Class c = MediaPlayer.class;
        Method m = c.getMethod("snoop", outData.getClass(), Integer.TYPE);
        m.setAccessible(true);
        m.invoke(c, outData, kind);
        return 0;
    } catch (Exception e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
        return 1;
    }
}

Answer 5

Look at http://code.google.com/p/moonblink/wiki/Tricorder for an example.

Answer 6

Basically what roskit said except with a minor return value modification from

return 0;

to

return Integer.parseInt( (m.invoke(c, outData, kind)).toString() );

In other words:

public static int snoop(short [] outData, int kind){    
              try {
                  Class c = MediaPlayer.class;
                  Method m = c.getMethod("snoop", outData.getClass(), Integer.TYPE);
                  m.setAccessible(true);
                  return Integer.parseInt( (m.invoke(c, outData, kind)).toString() ); 
              } catch (Exception e) {
               // TODO Auto-generated catch block
               e.printStackTrace();
               return 1;
           }
    }