I am removing commercials from a series of tv shows I taped onto a dvd-rw.  I tried unsuccessfully a couple of times to click on 'detect commercials,'  it sounds like the process is beginning a blank scene at the end of the tape is found but even letting the program run for 15-30 minutes, nothing else is found, and at times locks up.  I was able to successfully click detect scene changes and it took a while but found many scene changes.  I was able to detect commercials on another disc the other day, so I'm not sure how to rectify?