[XviD-devel] Comparison "old" vs "new" adaptive quant code

[Michael Militzer]

Hi,

> since I was collecting some "statistcal" relevant data for the use of
> h263/mpeg quant type in first pass when using modulated quantiser in
> second pass, I took the (CPU) time to do some further tests, see the
> results attached.
>
> I think this isn't a real valid quality-test because it just has an
> average quantizer as result, but you can see somehow why the "new"
> adaptive quant code somewhat worked (looking at the quantizer
> distribution it shows as well why it looked bad sometimes), and that it
> sometimes didn't work at all (Rush hour 2 result is clearly speaking for
> itself in that matter).

hm, the new adapt quant code produced higher average quants in both your
tests while resulting in 15% (or even more) bigger filesizes. Sure this you
did no quality test, but as adapt quant can currently only decrease quality,
I guess it's proven now that newer does not necessarily means better... ;-)

[...]

> A further note, if you take a look at the screenshots over at doom9 in
> the comparison, take a look at the brighter picture of XviD, there are
> strange yellow/greenish spots on the left side of the picture,
> alternating every pixel ("on-off toggle"). One user over at doom9 found
> some scenes where he could see that, and when looking at my clips I can
> verify that it's there sometimes. Is that intentional, a feature, or
> even a bug?

yes, it is a bug. The yellow line is caused by my yuv->rgb mmx
transformation code, so it's a decoder issue. A bugfix for this problem is
on my todo list, however I didn't looked into it yet cause I don't consider
this bug serious: As I said, it's no encoder bug, so the encoded content is
ok and has no yellow line. Additionally if you watch a movie, you'll most
likely do it in yuv overlay mode and the picture is ok then. So this bug
isn't a real problem unless you watch your movie in VDub and make
screenshots... - But I'll now try to add a fix soon...

bye
Michael