[insoluble]

Call me a skeptic, but there is no way there was an algorithm available to humans 10 years ago that reversibly compressed 6GB of unique, already-compressed media files down to 800MB. The only way this could have happened is if there were shared files or shared segments between the files. For example, if a DVD had a bunch of audio tracks but some of the tracks were basically just direct copies of the others, then the compressor could recognise the similarity and capitalise thereon. For lossless compression of general data, 7-zip set on Ultra is probably the best available right now. On the other hand, algorithms such as FLAC or PNG work well for losslessly compressing uncompressed media.