just look at it this way: Mpeg2 can take a television show and compress it down to say 10megabits per second. (these numbers are totally made up, I don't know if or how they may correlate to actual transmission numbers on DirecTV). A satellite transponder may have 40 megabits per second capacity, meaning you have room for 4 channels with the Mpeg2 standard I made up above. Mpeg4 is newer, and is designed to compress the same video at the same quality at a lower rate, meaning at the same picture quality, the mpeg4 stream is only going to take up 6-7megabits per second, making room for either a) more channels or b) better picture quality, as they could increase the bitrate and have a better picture.