burning vcd problem
 

I have some mpeg files which I ripped from my dvds. When I watch them with windows media player they are near perfect. However when I burn them to cdr's then watch them, sometimes (but not always) the sound is out of sync with the film! I think that maybe it has something to do with nero but I am not sure. Can anyone tell me what the problem could be? I cant understand why it does this only sometimes!