Winavi 10.5

I have installed winavi on my computer. I have vista 64. I have run the compatibly in the options to xp service pack 2. It works ok until I select autofit to a dvd. When I select that it converts an avi file to dvd. It says it was successful but when I burn it off using either imgburn or nero the picture jumps and it is unwatchable. If I select medium or high quality it works fine. Can anyone tell me why I get the problem with the autofit to dvd option