I used (on a Fedora Core 3)
- xine 0.99.4 to play the avi file
- KRec 0.5.1

Step 1:
	Open the video file in xine, keep it paused (Refer xine to get help with this!)

Step 2:
	Start KRec

	Step 2a:
		Go to the menu Tools>Audio Manager
	Step 2b:
		You will see xine in the list. Double-click it and change the Bus to in_soundcard

Step 3:
	Resume the video play in xine and start recording in KRec.

Step 4:
	After the playback is finished, you may export the recorded sound file to a wav format and later convert to mp3 !