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

Matthias Wieser mwieser at gmx.de
Thu Dec 15 19:04:52 CET 2005

Am Donnerstag, 15. Dezember 2005 11:00 schrieb Rich Felker:
> On Thu, Dec 15, 2005 at 09:50:17AM +0100, Matthias Wieser wrote:
> > Am Donnerstag, 15. Dezember 2005 08:02 schrieb Rich Felker:
> > > On Wed, Dec 14, 2005 at 07:52:34PM -0800, Corey Hickey wrote:
> > > > > Yeah, that does happen sometimes. I'm temporarily mirroring the
> > > > > attachments (with zip file extracted) at:
> > > > > http://fatooh.org/files/doom9tmp/attach/
> > > > >
> > > > >>Last but not least, I initially started reviewing with the VMR9
> > > > >> renderless renderer in MPC, but found that both Theora and
> > > > >> Snow (incidentally both decoded via ffdshow, where the rest of
> > > > >> the codecs was decoded by ateme's filters, plus AviSynth is
> > > > >> decoded by the Helix YV12 codec) were discolored,
> > >
> > > I'm confused... something other than lavc was used to decode lavc
> > > when doing the quality tests? If so, that will *OBVIOUSLY* make
> > > lavc look bad due to tiny differences in the idct implementations.
> >
> > Come on, it seems you are trying very hard to find excuses for lavc
> > slightly loosing against xvid.
> No, this is not "slightly", it's a HUGE difference.

Ateme's mpeg4 filter is not so bad. In addition, all other mpeg4 codecs 
would be affected the same way if Atme would use a strange dct. Most 
affected would probably be xvid because of xvid's additional "asm. vs. c" 
dct bug. If Atme supports FOURCC=FMP4 I think they have had done at least 
some basic quality assurance to make sure the output of their filter is 
comparable to lavc's own decoder.

> For YEARS AND YEARS all mplayer developers have known from experience
> that lavc is superior in quality to xvid,

This topic shows up on the mailinglists from time to time but I can't 
remember having seen numbers showing that lavc is better than xvid. All I 
have seen was "we all know that lavc is better than xvid and that's why 
lavc is better". Btw. does lavc support GMC?

> while windows users have 
> known the opposite. This idct discrepency would explain it.

Hm, many people use ffdshow for playback. Probably some of them use 
sometimes another mpeg4 decoder, too. If there really would be such a big 
difference in quality beteen ffdshow and other mpeg4 decoders somebody 
would have spotted this already.

> Just a few hours ago Dominik was reencoding a h264 file he had to make
> it playable on his "slow" laptop. He tried both lavc and xvid and got
> vastly superior results with lavc (2.32 avg quant versus 2.82 -- avg
> quant is generally not a good metric of quality, but with this much
> difference it probably is, and he reported the lavc file looked better
> too).

Very scientific test. Maybe he has used good lavc but bad xvid options. 
Maybe xvid does not like this particular video very much. Maybe ...

> So please stop trolling and accusing me of grasping at straws to prove
> lavc is better.

Please stop telling other people they are trolling only because they have 
an opinion different to yours.

> Those of us who know MPlayer know it is better,

Thank's that you repeate this "proof". I think, this supports my thesis.

> and if  
> it's performing badly in doom9's test we want to get to the bottom of
> his mistakes in testing methodology rather than accepting incorrect
> results.

I agree, but one has to accept that there is the possibility that there 
are other reasons why lavc loses against competing codecs.

If the decoder would be the single cause for this then it should be no 
problem to capture some snapshots which show the difference between 
ffdshow and atme's decoder. We don't need to guess if atme is good or 
bad. We can measure it.

Additionally we can investigate which features or settings made the other 
codecs look better - but just saying doom9 has done the comparison only 
99% correctly and taking this as an lame excuse does not help anybody.

> > For many years lavc did not even have an own FOURCC - it has been
> > nothing unusual to use any compatible Mpeg4 codec for playback.
> Yes, and it will look fine for watching. Doom9 is not testing casual
> watching. He's zooming in on single still frames.

But I doubt that slight dct differences might be the reason for losing 
against other codecs. At least the last comparison showed quite big 
differences - for example some video codecs did not show any raindrops 
while other codecs preserved those fine details. It's highly unrealistic 
that small, accumulated dct errors make raindrops disappear.

> And viewing on lcd 
> which hilights tiny artifacts that would be irrelevant on a nice crt.
> Anyway if you think it doesn't matter then doom9 should decode xvid
> with lavc and default lavc idct... :)
> Rich
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