DirecTV Moves to MPEG-4
Even more interesting was the announcement that these local HD channels would be encoded in MPEG-4 AVC rather than MPEG-2, which is the current encoding format. MPEG-4 AVC is more than twice as efficient as MPEG-2, which will allow more channels to be carried within a given bandwidth. However, current DirecTV HD receivers and dishes will not be compatible with the new signals; subscribers will have to replace their existing HD receiver and dish with a new one if they want to watch the new local HD channels. At this point, it's unknown what sort of upgrade path DirecTV will offer its current HD customers.
DirecTV's current national HD channels (HDNet, HDNet Movies, Discovery HD Theater, Universal HD, and ESPN HD) will remain in MPEG-2, at least for a while, so older receivers will still work with them. And the new receivers and dishes will be able to decode MPEG-2 signals, so new owners will be able to view everything DirecTV throws at them.