Audio recording doesn't work

I have tried to record video/audio using aurellum as described in page titled “Capture Audio/Video to a File”.
Video recording works fine. But size of audio file is 0. Size of audio file should not be 0 since I have added a background music.
I am using windows 7 OS.

My code is as:

     File video = File.createTempFile("JME-video", ".avi");
     File audio = File.createTempFile("JME-audio", ".wav");
     this.setTimer(new IsoTimer(30));
     Capture.captureVideo(this, video);
     Capture.captureAudio(this, audio);

ls -ltrah output

-rwx------+ 1 Administrators Domain Users 0 May 4 02:02 JME-audio375712088.wav
-rwx------+ 1 Administrators Domain Users 234M May 4 02:03 JME-video720577099.avi