AVI/DVD FIle size why so different

[targus]

Sorry if this is a dumb question but I was wondering why an Xvid AVI that starts life as 700Mb on my HD ends up taking up around 4Gb on the DVD.

That would be another little mystery explained!
cheers
\T

[thecoalman]

Bitrate x Length determines the filesize, makes no difference what format it's in. You could make the DVD file the same a s the Xvid doe a better job at lower bitrates the rsults would not be comparable.

[jimmalenko]

Short answer: Because XVID is around 4x more compressable than MPEG-2 for a similar quality.

Long answer: File-size is totally dependent on bitrate and running time. Since the running time is presumably staying the same in this case, it is the bitrate which must be increasing to cause the increase in file size. Tying back ino the short answer, you will require around 3-4x the bitrate used in a DivX or XviD to reproduce a similar quality MPEG-2 file in most cases. Of course this figure can vary depending on the quality of the source, and if you're using an all-in-one tool that is working everything out (with your best interests at heart of course) for you.

[kschang]

Or a very short answer: You can't compare XVID/DIVX, which are MPEG4 based formats, with MPEG2-based DVD. That's comparing apples and oranges.