Sonic wont decode and burn the file for you...
You need special software for that..
Take a look at dvdsanta it is very basic and will convert and burn movies in 2 easy steps...
The demo version is a full version and it does not expire, the only thing is it has demo at the top of the screen in small print on the output video, but you can over come that by zooming in a frame with your dvd remote....
http://www.dvdsanta.com