Adam T Lindsay has written an interesting post on how the iTunes Store could deliver high definition for the AppleTV, in which he speculates that Apple may make use of Scalable Video Coding (SVC), an extension to H.264.
The idea around SVC is that you have a normal H.264 base layer, and you can add enhancement layers on top of it, whether they be spatial, temporal, or SNR enhancements. That means that you can improve the resolution, frame rate, and/or picture quality by adding additional streams to the base layer. Consider that the 640×360 standard 16:9 videos have half the pixels in each dimension from 720p videos with 1280×720. This is perhaps the most basic application of spatial scalability, but it's also very relevant. I find it very easy to imagine an additional "track" in QuickTime that fills in three additional pixels out of every four. If a computer (say, my G4 PowerBook) is incapable of handling the full high-def combined stream, it can conveniently fall back to the base layer.
This sounds plausible to me, though Lindsay does wonder at how the audio side of high definition might work in this situation.
He also speculates on a Quicktime upgrade to version 8, a new version of iTunes, and an announcement of movie downloads in Europe, all at the same time.
Interesting thoughts.
From: Sony to double BRAVIA LCD TV production for growing European demand