Mpeg files are not easily edited, even with programmes which say they do it. Some of the problems lie in the way the Mpeg file is made up. An Mpeg has i,b,and p frames. Editing cuts can only be made at the i frames, which is the only true frame in the movie. This is unlike an avi file where each frame is like the i frame and cuts can be made anywhere.
Mpeg2 files use programme time stamps to keep the audio and video in sync. Therefore when making your edits to the mpeg file when you preview in your editing programme or in the computer dvd player, before burning, the audio and video always appear to be in sync.
The problem comes along when the Mpeg2 files are authored to the dvd and burning commences. In the authoring, the VOB files which are created, discard the programme time stamp information and this can lead to very small audio and video sync problems. The more edit points there are, the greater the problem will become. Straight cuts are generally not as bad as using transitions at edit points.