If the source files have corrupt frames , sync canbe messed up when being encoded to dvd, mp4 or whatever. I record freeview streams a lot on the computer and these are packed with errors especially channel 4, although you dont usualy see them durring playback. My solution is to run the rewcorded mpeg files through VideoRedo quickstreamfix which takes away the audio frame where theres a bad video frame (or it can replace the frame). The errors are largely where the adverts are inserted so dont notice any problems on the destination file.