[MEncoder-users] new doom9 codec comparission (submission)

Mathieu Monnier manao at melix.net
Fri Dec 16 23:16:09 CET 2005


> XviD: http://img39.imageshack.us/img39/3341/154xvid6xt.png 
> libavcodec: http://img39.imageshack.us/img39/4590/154avcodec2da.png

Fair example

>> XviD: http://img39.imageshack.us/img39/6135/283xvid3tg.png
> libavcodec: http://img39.imageshack.us/img39/573/283avcodec5xl.png

Not so fair, both are as worthy imho

Btw, how did you get that posterized look for your screenshots ? Did the
source looked like that ?

> As you can see, the ones decoded with the 'wrong' idct look bad in 
> the same way (or at least a very similar way) that lavc mpeg4 looked 
> bad in the doom9 tests!

Definitely not. In Doom9 test, when he criticizes FMP4, it's for a lack
of details. Idct mismatches don't make details disappear. They create
chroma drifts, and additionnal noise. What I see on screenshots where 
Doom9 points a lack of detail is flat blocks ( and that's without 
zooming, but on a LCD ).

> I am by no means positive that this is the problem,

And me even less positive than you.

Loren has given a possible reason for the assumed inferioty of FMP4 in 
Doom9 test ( bframes ). Here's another : rate control.

You don't know the quantizer at which the frames have been taken, you 
don't know the quality of their preceding frames nor their type. So why 
care about what they look like. You'd better read Doom9 comments ( when 
there are - for this pretest, he's been quite shy it seems ), they are 
much more important and a far better indicator of the relative quality 
of the different codecs.

> but I definitely think it's worth investigating more.

>>> But the last straw is that I actually tried ffdshow. I watched 
>>> the lobby shootout again, XviD and lavc only. Now that makes two 
>>> scenarios where XviD would have a so called disadvantage, yet
>>> despite that it still looks better
> I thought you said that you weren't able to get proper screenshots 
> using ffdshow...?

So it has been invastigated more, yet you don't think it's enough, and
you even doubt his words ? Where did he say he made screenshots ? Why 
would he need to make some to spot the lack of details ? Can't he simply 
use the pause button ?

>>> So you see where I'd be having a problem with your argumentation 
>>> that the comparison isn't fair. If it isn't fair, the what 
>>> Michael asked me is to skew the results of the entire comparison 
>>> in favor of lavc. Is that what you're saying?  And consider the 
>>> implications of that..

There I disagree with Doom9. Libavcodec allows to decode all MPEG4
codecs as fairly. It's a glitch in ffdshow that makes it not usable for
the comparison, nothing else ( hence, he's argued a bit too far ).

>>> According to this logic, since I used the ateme decoder, ateme 
>>> should've had a significant advantage over the two other ASP 
>>> codecs in the qualification. Yet why is it that I would put it in
>>>  place 3 out of 3?

> Probably because the ateme encoder sucks. Matching idct 
> implementation will not make up for an encoder that otherwise sucks.

Yeah of course it sucks. You can also read the test to from head to tail
and see that it is 5 times faster than FMP4. So perhaps it only has a
different speed quality tradeoff.

> We do not endorse quicktime (aka mp4) format whatsoever. In fact it's
>  widely considered the be the absolute worst container format out 
> there.

First time I heard that one. He raised an issue which is present
with any container anyway since it's the mpeg4 standard fault. But you
end up bashing unwarrantedly the MP4 container.

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