wierd question for burning dvd's

alright so i was looking to burn some movies onto dvd's....but apparently the files uncompress when you try to burn them. Was wondering if it was possible to compress the files before burning them. I just want them to run on a computer, not a dvd player. I just think it's wierd that a 700 meg file can burn on a cd, but when you try to burn to a dvd, it explodes to like 4.5 gigs or so. anyone have any insight?

(no these movies aren't illegel. i own all of them. just would like the good ones on a couple dvd's as apposed to like 15 or so)

thanks in advance

I'm not exactly sure what you're doing. You got some avi/mpg files, correct? And you're just trying to burn them straight to dvd? or make a dvd movie out of them? What software are you trying to use to do this?

yea i'm trying to put a few avi's on a dvd...i was wondering if there was a way to compress them before burning them. on my computer one shows up as 700 megs...when i load the file on nero it goes up to about 2.05 gigs. i want to put as many avi's on one dvd as i can. does anyone know what i'm talking about?