Your last questions somehow got missed in what were otherwise very helpful responses. Anyway... my experience has been that AC3 is very very slightly smaller than MP2, maybe only 2 or 3% smaller. You'll save space with it, but not a lot. MP3 is absolutely unsupported for DVD. I am not aware of any DVD authoring programs that will allow you to use it. Even if you could do it, you are unlikely to find a standalone DVD player that would play such a disc.