I'm using Virtualdub to retouch a captured video taken from a videocamera (analog input). The operation I perform is a simple cutting of bad or unwanted frames from the movie; sometimes I have to remove some seconds from the original movie. To do this I usually press the CANC key on the frame I want to delete or mark in and out a region and I delete it always using the CANC key. The original movie is MP2 DVD compliant or AVI DIVX, recorded directly using an ATI VIVO VIDEO CARD. After removing all the unwanted frames I usually save the video as DIVX. The problem I encounter is that when I save the whole video (approx 40 min) or part of it, the audio is no more sinchronized with the video, it seems that the anticipation grows going from the beginning to the end of the movie. After 40 minutes I get a difference between audio and video of more than 1 minute!
Does anyone know the reason of this problem?

Thank you, regards