when backing up just the "main movie" and no compression the back-up DVD video skips and jerks while audio stays smooth. The video is fine until approx. the 30 min mark. The uncompressed movie is approx. 3.8 GB in size and the target DVD-R is 4.7 GB. I am using DVD shrink 18.104.22.168 and nero version 4. What is my problem?