Just did a quick test 320x200x8bit grayscale PNG (couldn't quickly figure out how to get 8bit color pallet) compressed to ~15-40kB. Multiply that by 60frames a second (or whatever odd framerate historic hardware used) and 120seconds and you get 200MB. Not completely impractical, but I wouldn't call it trivial amount of space. And if you find any demoscene collection providing losslessly compressed videos let me know. All I have seen is original executable+youtube video (which suffers from compression artifacts). And I doubt many demoscene website maintainers are eager to increase their storage and bandwidth costs 100x.