A dumb question about DVD Capacity.

Question

I want to create as high as quality DVD as possible from my iMove (5.02) project using iDVD (5.01). I've started off using DVD+R disks and I'm now considering using Dual Layer DVD's.
The actual iMovie file size of my project is 12Gig at about 60 minutes. It's the same size when I SHARE as a full quality QT file. However when I create an iDVD Project from either the QT file or directly out of iMovie, my DVD Capacity reading is approx. 2.1 of 8Gig.
Now my question is this: What exactly am I reading here? I was under the impression that the DVD Capacity indicated the size of the movie. Obviously a 12Gig movie isn't going to fit onto a DVD, so I assumed that this reading related to the compressed size, but am I wrong? I can't understand why a 12Gig movie would need to be compressed so much. If this is the compressed size, then how can I get iDVD to not compress it so much? I've tried using Best Performance as the encoded setting, but would expect something up in the 6-7Gig range.
If I use a dual layer disk, am I only going to be writing a 2Gig file to it?

Answer 1

Thanks.
But two questions.
My iDVD Capacity status bar reads this file as 2 of 8 Gig. Is it telling me that my imported iMovie will be compressed down to 2Gig, if so then why is it compressing the file down so much, OR if not what exactly is this information telling me? If I should expect a reasonable good compression from a 12Gig movie down to say 6 or 7Gig why isn’t it shown in the iDVD Capacity status bar?
Also, at what point does iDVD work out the compression? I don’t usually insert a blank DVD in until I go to burn the project and iDVD requests one, up until that point how does it know what size disk I’m using 4Gig Single or 8Gig Dual Layer.