AVCHD Question

A

Andrew McCarrick

Carbonite Member
Is AVCHD a variable datarate codec? I'm curious in the sense, if I take a PAL model of a camera and a NTSC model of the same camera; will the PAL model pull a better datarate per frame compared to the NTSC model? Both cameras (Sony CX550V and Sony CX550E) have the 24mbps mode. So the main question is will 50i on the PAL model provide any better performance then 60i on the NTSC model?
 
Doesn't work that way. Bandwidth isn't allocated per frame, it's allocated per group of frames. And while in an intraframe codec you might have a point, in a long-GoP codec it doesn't really matter. Long-GoP compresses the changes between frames. 60i has more frames per second, with less change between frames, and the less change, the easier to compress. 50i has fewer frames per second, but with more change between frames. So each frame is harder to compress, but there are fewer of them. So in the end it should net out about the same.

The only thing that makes a real big difference is interlaced vs. progressive. Interlaced is inherently harder to compress, and the chroma sampling scheme in interlaced is awful. Progressive compresses better and cleaner and the chroma sampling turns out nicer.
 
Alright, that makes sense. Thanks.

Would it make sense to shoot in 50i, convert to 25p (for a PAL release and to stick as close to 24p as possible), convert to 24p for a film out, and then convert to 60i (through 2:3 pull-down) for an NTSC release?
 
No, never shoot interlaced ever under any circumstances if there's a reasonable alternative.

Shoot 24p for a worldwide release. Every DVD player in the world (well, almost every one) can play a 24p-authored DVD, including PAL ones.
 
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