Nick:
I did not want to leave you hanging as I have pondered on this last night. I read your reply and that fact that you are able to view on your computer with no problems just puzzles me more. I know that there are many more on this forum that have a much better grasp of this and hopefully someone will be able to help.
Obviously something is being screwed up during the rendering/transfer to DVD. Have you possibly tried different DVD media? The only other thing I noticed is the USB DVD external burner. Could that be the cause
: I know I am pulling at straws but really I have not a clue and sorry I cannot help in this area.
Wish you well and hopefully something will come from this.
Scooter