weird question on file sizes

[rsuave5]

okay when im building a movie from clips i have from my vhs i capture edit etc and when im done ill look at file size and it will say 8 gigs, then i drag that file over to my burning program and it says it will only take up 4 gigs on the disk!!?
the same goes for stuff i get from my mini cam and even weirder when i copy a dvd-r i must have over double the space of the dvd on my harddrive. why does a 4 gig dvd take up 8 gigs on my hard drive? it stores it in a temp. file until it burns and deletes but i check the file and its always almost double the actual size? anyone know why?

[roosh2]

post your hardware...