[theora-dev] [OT] Just saying hi!

Mike Melanson melanson at pcisys.net
Wed Feb 26 11:09:19 PST 2003

On Wed, 26 Feb 2003, Christoph Lampert wrote:

> ffmpeg (and therefore automatically mplayer-) support could _really_
> boost popularity... good idea!

        And xine, don't forget about xine (my adopted project...:)

> That seems to violate a big rule for fast routines: locallity!
> You have to store all coefficients of all blocks before reconstruction can
> start. Why was it chosen that way? 

        You're asking the wrong person. But that same question occurred to
me. My best guess, as indicated before, was that is was chosen as a novel
way around possible patent ramifications.

> I myself am most involved into motion estimation, so as final questions
> before letting you get back to work: Is the general method for ME
> similar to MPEG? I-frames (golden... I like that... ;-) , P-frames,
> B-frames? Motion estimation is done blockwise? Is there support for
> global motion? 

        I haven't gotten too much into the motion stuff (getting close to
decoding keyframes right now). And I'm still a little fuzzy on motion
esitmation/compensation in general. Can you give a brief synopsis of how
ME/MC stuff operates in MPEG variants, particularly where half-pel and
quarter-pel prediction figure in and how SIMD averaging instructions help
with that?

        I can tell you that VP3 has I-frames that have to persist until
the next I-frame is decoded. Every successive P-frame can use information
from either the previous P-frame or from the most recent I-frame. I can
also tell you that the maximum range of a motion vector appears to be
+/-31, according to my old notes on the decoder:
Also, the decoder has code to support sub-pixel motion compensation, but I
have not gotten to investigate that too deeply yet (which is why I was
hoping you will be able to fill me in on the MPEG methods).

        Hope this helps...

	-Mike Melanson

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