[Theora] Ogg Theora: Some questions on codec interna

Ralph Giles 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 
bitrate though.


More information about the Theora mailing list