I have a small problem I'll hoping y'all can help me with.
I am in the process of building my DVD, and everything is fine, just barely under the max space allowed by my DVD. I noticed a mistake in a small audio clip, and I replaced it with one that was bout twice it's size from 25mb to 50mb. When I went to build again, Encore said I was over the spacial limits of the DVD. When I checked the Disc Info, it jumped from 4.69gigs to 4.81gigs. I jumped more than the difference between the two files. So I have been importing compressed video files to Encore, but when I replace an 8gig file with a 2gig file, there is no change in gig's used in the Build/Disc Info panel.
The size of your source files isn't really relevant when authoring a DVD, unless the assets are already DVD-legal, which means they will not be transcoded by Encore. Their duration is relevant. There is a whole topic about this, called bit-budgeting. A Google search will reveal much information.
You didn't provide much detail, but it sounds as if you are using highly compressed sources. I would advise against that, if possible.
So a good rule of thumb is use asset durations and bit-budgeting calculations to determine the size of your DVD - not the original size of your assets.