I am very excited about the HD codec. I was getting very worried that M$'s HD codec was going to be ratified, but this gives hope the more open-standards version from Apple will have hope.
I'm a little confused right now about HD in terms of all its variants, including HDV, as well as what the HD codecs will mean for next gen DVD viewing. Presumably there will have to be one, and only one codec, like MPEG-2 is now for DVDs. Let's hope it's Apple's version, otherwise my future in media authoring is going be hell.
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I am no Shake expert by any means. In fact, I really don't know much about it, but I get the impression it's meant more for traditional film-style compositing (color correcting, blue screening, layering multiple footage sources as though they were one (like the armies in LOTR against the New Zealand scenery), motion tracking, perspective distortion correction, etc.). Motion would specialize more in Motion Graphics, espeically thanks to pre-built animations for text, logos and art. Certainly, they share features, much like Garage Band and SoundTrack share features. They are just better different things and focused toward slightly different audiences.