[Theora] Ogg Theora: Some questions on codec interna

Gernot Ziegler gz at lysator.liu.se
Mon Sep 20 02:43:35 PDT 2004

Hej Ralph !

> See http://www.v2v.cc/~j/Theora_I_spec.pdf for the gory details.
Jupp, already looked into it :-)

> supporting 16 bit or float samples and letting the compression take
> care of any excess precision, instead of fiddling with half-measures
> like 12 bit samples.
Completely reasonable !

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 ?

> However, there's also a 'delta png' option where each frame is
> subtracted from the previous one and only the difference compressed
> (in a lossless fashion like png). And it has animation support with
> compositing of arbitrary layers that could in theory be used to remove
> redundancy by an intelligent encoder.
Interesting - I just had a look at the MNG overview and saw that it was
_much_ more advanced than I thought it to be, so I will investigate that
further :-)

> 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" ? )
M-JPEG is no option as it would also compress the depth data with JPEG,
which is DCT-based, which is bad ;)

> There's also a draft spec for mng-over-ogg already, which I need to put
> back in the wiki, so there's only your implementation to be done.
ok !


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