[MPlayer-dev-eng] Re: [MP] Re: [MP] [PATCH] "turbo" mode

[Matthias Wieser]

Am Mittwoch, 15. September 2004 22:01 schrieb Guillaume POIRIER:
>
> > And you should evaluate the PSNR differences between individual
> > frames.
>
> How do I do that?

Add "psnr" to your lavc options. Then you will find a file named like 
"psnr_342234.log". This file contains psnr numbers for each individual 
frame. You could plot those numers, calculate differences between 
different passes/options/... and so on.


> How may that be reverent ? Do you mean that given 
> that the statistics are not as good, maybe say, first frames lack/have
> too much bits?

Maybe a normally good looking scene gets even more bits. Then the PSNR of 
the frames of that scene would be higher but there would be nearly no 
visual difference. But those bits are not available anymore for scenes 
that would need them. So maybe the mean PSNR would be the same but the 
visual appearence could be worse.

> > It could be possible that mencoder in turbo-mode thinks that some
> > scenes are extremely bitrate demanding but with the options of pass 2
> > the scene isn't difficult to encode anymore. So your patch might
> > change the distribution of bitrate in a way that leads to only
> > slightly lowered global PSNR but to some really bad looking scenes.
>
> Then, could you tell me what flags really should be left untouched?

I don't know. Maybe one could plot psnr versus time and compare different 
options. If an option influences the shape of the PSNR distribution, this 
option should be left untouched.

        Matthias