here is the way to to that

1) mplayer -dumpaudio AVI_FILE_NAME.avi -dumpfile MP3_FILE_NAME.mp3

Now we have the whole audio data from our video on MP3_FILE_NAME.mp3

Now using mp3splt we can isolate only the part we want like this

2)mp3splt MP3_FILE_NAME 10.23 11.24

10.23 =minutes.seconds

If the part we want to cut stars on 1:25:12 we well write is as : 85:12

Now a new file with the name MP3_FILE_NAME_1030_11_24.mp3 created with the audio part we wanted