What part is actually compressed when watching DVD rips?

[pimvda]

I was wondering, normally official DVDs are about 8 gb if I'm correct. Most recordable DVDs are about 4.4 gb. When a DVD is ripped and recorded on a 4.4 gb disc, what part is actually compressed or left out?

 

[sparky77]

If your using software like dvdsrink to make a backup copy it would be compressing the video and generally leaves the audio unaffected. If you happen to be downloading copies off the internet they are usually compressed using Divx or some similar codec, and in that case the video and the audio are both compressed.