[Theora-dev] Patch that fixes distortions during static scenes

[Andrey Filippov]

> On the other side, other keyframe-related artifacts are in place,
> and I see a problem which is quite opposite to one you descibed.
> It looks like a keyframe is being encoded with a "too bad" quality,
> so that the following frames gradually improve it.

Hi Ivan,

I'm seeing the same while troubleshooting FPGA implementation and have a
particular suspicion - in time I'll test it. I'm now working with maximal
quality (63) and have a bit-to-bit matching of the restored YUV data and
the camera internal one. And if I'm right it is not easy to fix w/o
changing the specs.

It is subtracting DC (average value) before the forward DCT and adding it
back after the inverse one. The average value does not need to be precise
- enough is to have integer one, so the DCT will still produce some
"fractional" DC output - both should be added.

I used this technique when making JPEG implementation and it really helped
(but to be honest I had less bits in cos/sin constants).

Andrey