I once tried to compress a super-bit disk to fit a 4.7gig single layer disk and the final version had numerous artifacts. And why not... it was compressed to about 55% of the original. I always wondered if I should have compressed as an mpeg in two steps... from 9gigs to 7, then down to 4.7gigs. I never got around to doing such an experiment. Well I wonder about the value of pre-compressing large files before encoding to DIVX/XVID. Has anyone tried it?
Well I had to try. I took an original mpg and tried to encode it in DIVX and to get a set file size the video bitrate would have been 1450kBs. I then compressed that mpg to 90% of the original size and then again to encode to that same DIVX file size. The video bitrate again would have been... 1450kbs. It made no difference. I don't yet understand why but let me see if this analogy makes sense. Borrowing from jpeg compression... when I open a jpeg in Photoshop it says its uncompressed sized. It remains the same even if I compress it to 50%. So maybe something like this is happening with video as well? That it's not the original's compressed size that matters... it's the uncompressed size? Does any mpg source have to be uncompressed first before being reencoded into DIVX or H264?
