[Theora] Ogg Theora: Some questions on codec interna
giles at xiph.org
Mon Sep 20 11:15:59 PDT 2004
On Mon, Sep 20, 2004 at 11:43:35AM +0200, Gernot Ziegler wrote:
> Actually I like the codec's style of omitting interlaced handling and
> B-frames, makes the format much more simple - but how do you handle
> interlaced material then, and can you achieve the same compression as MPEG
> even without B-frames ?
Yes, it is a nice simplification.
According to Dan Miller, who worked on VP3 at On2, they didn't need them
to match MPEG. Instead theora can refer to the previous I frame as well
as the previous frame. We could perhaps do better with B frames, but not
enough better to warrent the complexity.
We deal with interlaced material by de-interlacing it before encoding.
This a general philosophy with both theora and vorbis: keep the decoder
simple, but flexible, and put shift as much intelligence and
decision-making to the encoder as possible.
Generally, for playback on any progressive-capable device, this is what
you want anyway. Playback to standard televisions (set-top box
applications) is really the only place being able to directly encode
interlaced material makes any sense.
> > So, you have a range of options, but it's unlikely to do better than
> > mjpeg in terms of bitrate unless a large part of your sequence is
> > static or a simple pan. But no problems with deep image support.
> ("deep image support" = " 24 bit per pixel" ? )
"deep images support' = "more than 8 bits per sample", up to 64 bits per
pixel in the case of MNG (RGBA).
> M-JPEG is no option as it would also compress the depth data with JPEG,
> which is DCT-based, which is bad ;)
Hmm. Right. I wonder if you could experiment with 'fixing up' the jpeg
depth with additional composites? Might not be too effective in terms of
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