The Next Generation Starts Here!

I thought regular DVD used Mpeg2? Isn't Mpeg 4 compressed more efficiently than Mpeg2, i.e. smaller file sizes? So why can't they fit more than one movie on a disc?

 

Regular DVd does indeed use MPEG2, and MPEG 4 is more efficient. The reason they can't fit more than one movie on a disc is that the resolution is approx 4x higher, therefore (obviously) takes up more space.
Also, if a 90 minute film is encode at N bits/s, this will also obviously be constant between both MPEG4 and MPEG2, however the MPEG 4 quality will be better. The only reason that movies using MPEG4 don't reduce the bitrate so it looks like MPEG2 and fit more on one disc is that the main selling point of both HD formats is quality, so the better the quality the more likely it will sell - in a few years if and when it becomes ubiquitous I'd expect a few multiple film disks.

 

Ok, I think I understand now. So even though it's using a more efficient codec, the uncompressed movie has four times the resolution, thus the file size is larger.Still seems to me even if a movie is four times larger there should still be plenty of space left over.