[MPlayer-users] Re: encoding quality - bpp, resolution, quantsand quality

HR haavroed at online.no
Thu Sep 11 21:33:15 CEST 2003

> From: Tuukka Toivonen [mailto:tuukkat at ee.oulu.fi] 
> Smaller q is better image quality. Since almost all 
> quantization parameters
> are at 2 and 3, the quality should be very good.
I know, but read on and you'll see the reason why I ask.

> >Does this mean I should decrease the resolution? If I 
> understand other
> I suspect it would not help. You could try encoding with 
> lower resolution
> and the same bitrate and see which one looks better, if you have time.
> Otherwise, don't bother, it's probably good already.
Dont think I'll bother. And like you say, it's already good. Very good.
I was just puzzled by the fact that the encoding-tips.txt states

e.g. the lowest quantizer (vqmin=2) gets used for > 95% of the frames
then you can safely increase your picture size."

Implicitly, this means I should scale down. Isn't >95% q=2 a rather
extreme measure? When should I *stop* increasing the picture size then?
At >50% q=2? Would the use of q=2 increase very rapidly as the movie W:H
decreases just a little? Again, I can encode to test, but if some of you
know the answer, I can use my time for something else.

I also encoded the same movie with

-xvidencopts max_key_interval=125:bitrate=1802:me_quality=6:4mv (with
passes 1/2)

for comparison, and I honestly cannot see the difference... havent
studied it thoroughly though, just browsed through briefly, looking at
dark areas, smoke/clouds, water, edges with high color gradients and
such... what should I be looking for? Maybe the bitrate is too high for
any differences to be easily noticed?

I used the same scaler in both encodings (-sws 2).

If I have time to spare some day, I'll extract some frames and arm
myself with a microscope and some image analyzing tools... :p~

> trell and vpass for two/three pass encoding would be very 
> good. Also -vf
> hqdn3d, if it is TV source (probably not good if it's from DVD).
It's a DVD encoding. And always use 3pass (audio + vpass=1/2), I just
didn't paste it in... ;)

How useful is trell for DVD encodings? Should be less noise there than
from a TV/VCR source? How does digital TV broadcasting fit in here?

I also considered using mbd=1, or is that the default when using vhq? I
mean if there's a difference between the "vhq" turned on by mbd=1 and
the vhq parameter, what is it? And if not, do they work well together?


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