Thx for your answers everyone! My mom has a dual-layer DVD burner in her computer and I have a single layer. I like backing up my DVDs so when my brother borrows them he doesn't ruin them, so I normally use vobcopy+transcode+mplex to do this. She never uses the DVD burner for single layer discs, never mind dual-layer, so I was thinking of switching them. Sometimes, though, mplex has trouble making the audio and video sync properly. It would be much easier if I could just use vobcopy and then dvdauthor/dvdstyler to reburn the disc.
EDIT : Lol, this post made no sense. Essentially, I don't want to have to use transcode when backing up DVD's