[Theora] Ogg Theora: Some questions on codec interna

Gernot Ziegler gz at lysator.liu.se
Fri Sep 17 03:10:18 PDT 2004

Hej Ralph !

Thanks for your extensive reply !

> So you'd be using your own wavelet codec to encode the Z channel
> instead of theora? Either way, yes that's perfectly fine. The Ogg
> terminology is 'two logical bitstreams in one physical bitstream'
> but it means the same thing. :)
I rather meant to ask which kind of internal compression algorithm you
use, and then decide on it - I presume that it is DCT-based, then ?
Writing my own wavelet codec - brrrr, won't happen soon ;) ... no, in that
case I would try to fit some other bitstreams into the Ogg "carrier", like
I did with PNG before :-)

> > and he is looking for video format that is capable of encoding 12 bits.
> 12 bits doesn't seem like very much. :)
(gah, I know that would be joked upon, exactly when I hit "send" ;) )

> We've no plans to add support for more than 8 bits-per-channel Y'CbCr
> to theora, but it is on the requirements list for our vapourware
> next-generation 'tarkin' codec. We do support deep image sequences
> through MNG, but that's much higher bitrate than theora. Likewise with
> encoding the residual in a second stream.
Ah, so tarkin is still alive ?

The thing is that not even MPEG-4 seems to have seriously considered > 12
bit compression, see

The N-Bit Visual Profile adds support for coding video objects having
pixel-depths ranging from 4 to 12 bits to the Core Visual Profile. It is
suitable for use in surveillance applications.

That is the only minor side-format that does so, if I got it right.

And, honestly, I would rather use a patent-free codec for my research work
than something encumbered by large-company-patents ;)

MNG (based on PNG, right ?) does not do interframe compression, or does it

> You might hit up the dirac(.sf.net) people; I think they have or
> planned support for at least 'broadcast quality' which is typically 10
> bits per channel. Their code might be more adaptable to this.
Thanks for the tip !

> You're welcome to give it a try, of course, and we'll help as we can.
Thank you very much !

> Adding extra streams is easy. Adding 12 bit support is probably a big
> format change, but the actual code modifications would mostly be of the
> tedious sort (type promotions and so on). You would probably want a new
> mdct too. Derf?
I know DCT and iDCT, what's an MDCT ? ;)


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