The files on every DVD are different, some larger, some smaller. Menus, audio tracks and extra features can add to the total size of the disc. The larger the original disc, the lower the "Quality" number when you copy to a DVD5 SL. The lower the "Quality" number, the longer the processing time and the lower the quality of the video on your backup copy. 100% quality=no compression, fastest processing, best picture quality. This is why there are functions in Platinum that allow you to make the files smaller, and make "Quality" hgiher, (Main Movie, Customize) if you do not want to use a DVD9 DL.