When importing dvr-ms files made by Windows Media Center in to Roxio Video Copy and convert, the program does a "Remux." However frequently when I make a copy in WMV or MPEG4 formats the audio gets and get progressively further out of sync as the new file plays. It can be out by as much as a second. It doesn't do this all the time and I can't find any particular pattern. Some video imported from DVD also goes out of sync.

Any clue as to what causes this or how to solve it?

Easy Media Creator 10 Build 100B44B ENU
HP Quad Core computer
64 bit Vista
4 gig of memery