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

[Matthias Wieser]

Am Donnerstag, 15. Dezember 2005 20:55 schrieb Rich Felker:
> On Thu, Dec 15, 2005 at 07:04:52PM +0100, Matthias Wieser wrote:
> > > > 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.
>
> What would FOURCC=FMP4 mean? lavc has several different dct
> implementations and the user can choose among them. AFAIK the selected
> one isn't even stored in the file, and which one is used may depend on
> the os and cpu platform.

If not specified otherwise the dct is selected by mencoder ("Automatically 
select a good one (default)."). If this causes significant quality 
problems then the lavc encoding guides and the mencoder documentation 
should be updated.

>
> > > 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?
>
> Decoding, of course. Encoding, no.

:-)

> GMC is not useful and wastes a huge amount of resources at decoding
> time.

Only few features are for free. On the other hand GMC can improve quality 
a lot.

> > > 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.
>
> It is NOT A BIG DIFFERENCE IN QUALITY!!!!!!!!!!!!!!!!!!

Then let's wait for the Doom9 results. If xvid only wins by a diminutive 
margin then I have no problem with excusing this by not using the native 
decoder.

> Like I said, if you watch movies like a normal sane person you will
> never notice it. When you notice it is when you do idiotic things like
> saving single still frames and zooming them 4x in an imageviewer!

[...]


> When the thread about xvid dct came up on ffmpeg list, I could not see
> the difference in the two images without looking very closely, but the
> guy who posted the "bug report" thought it was very important and I'm
> sure pedants like doom9 will too.
>
> > > 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 ...
>
> It's not scientific, but once it happens enough it becomes common
> sense. This is the common sense of the developers which has built up
> over years and years of examples.

Haha, maybe you should ask the xvid developers which they think is the 
best codec. Their answer will be based on "the common sense of the 
developers which has built up over years and years of examples", too. :-)

So which group of developers is right?

> We see xvid files off the net from 
> "professional" encoding groups, and then make lavc encodes that look
> much better, etc. etc. etc.

>
> > > 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.
>
> Having a different opinion is not trolling. Belittling my opinion and
> accusing me of exaggerating and grasping at straws is. I want this
> matter investigated properly, that's all.

I wrote that it seems you are trying very hard to find excuses for lavc 
slightly loosing against xvid. Maybe I misinterpreted your posting. I 
don't know. I only know that the comparison did not even start. There are 
no winners or losers. Only the hint, that xvid 1.1 seems to do very good. 
Using a common decoder for all mpeg4 codecs might be questionable but it 
should not only affect lavc but all mepg4 codecs.


> > > 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.
>
> Yes and I'd like to see why. But judging from experience I'm nearly
> sure that it's bad testing methodology of one form or another.

If lavc is not recognized as the best mepg4 codec of the world then it's 
either the user's stupidity or bad boundary conditions or bad testing 
methodology or to old software revisions, or... But we all know that lavc 
is the best of the best. Amen ??!

>
> > 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.
>
> I never even heard of atme before this test, wtf is it?

A large company doing hardware and software codecs.

>
> > 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.
>
> There's no such thing as 99% correctly. Either a comparison is correct
> or it's not. If it's not then the results are meaningless.

You wrote: "It is NOT A BIG DIFFERENCE IN QUALITY!!!!!!!!!!!!!!!!!!"
If it's only a very very small difference in quality and xvid and divx6.1 
winn hands down then it does not matter if the atme od lavc decoder has 
been used.


> > > > 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.
>
> This is because you're just flaming rather than knowing the theory and
> reading the relevant threads and looking at the sample images that
> SHOW THE DIFFERENCE.

Wait for the results and stop accusing other people of flaming. Yes, I 
doubt that slight dct differences might be the reason for losing against 
other codecs. Because dct differences generally are small compared to 
quality differences of video codecs.

You are constructing a special case where only lavc suffers from using the 
atme decoder while all other codecs show good quality. That's highly 
unrealistic.


> > 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.
>
> We're only talking about two codecs here, lavc and xvid. I haven't
> seen doom9's screenshots. Would you care to point me at them.

http://www.doom9.org/index.html?/codecs-203-1.htm
Scroll down by 2/3.