[theora-dev] Updated VP3 Document

Mike Melanson melanson at pcisys.net
Fri Oct 10 10:36:34 PDT 2003

On Fri, 10 Oct 2003, Timothy B. Terriberry wrote:

> Didn't read too deeply yet, but a few comments on the Theora differences 
> section:

        Neat. This is the kind of feedback I was hoping for. I haven't
gone too deep into the Theora stuff yet but I wanted to get a placeholder
in the document for it.

> 1) We plan to fix the frame orientation to conform to that used with VP3 
> before the beta (most likely in an alpha3). We want to preserve the 
> ability to transcode from VP3 losslessly, and there's no real reason to 
> keep two different orientations around.

        No real reason other than it makes more sense to render from top
-> bottom. I won't dwell on the issue, though. I thought Dan Miller was
proposing a header bit to specify frame orientation; what happened to that

> 2) Theora stores the prefix-free codes directly, in the form of a full 
> binary tree (this is a change from alpha 1, where the histograms used to 
> generate the prefix-free codes were stored).

[should I be paranoid about the absense of item 3? :)]

> 4) Theora removes some of the unused bits in the VP3 frame header. There 
> are still 3 0 bits in keyframe headers (keyframe type, which is always 
> 0, and 2 unused bits), but the others are gone.

        Thanks for the feedback...

	-Mike Melanson

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