using a sh*t load of compression is how.
[same as how you can fit a 640MB CD of music into a 64MB (or worse 32MB) flash memory card in mp3 portables].

You're right though, a CDR version of a dual layer DVD movie wouldn't be very watchable IMHO, probably have compression artifacts everywhere, single sound track (stereo maybe if you're lucky), and little else.I think I'd rather have the real movie on DVD thanks.