[MEncoder-users] on psy_rd

[Matyas]

Grozdan wrote:
> of course psy-rd will have an effect on the bitrate. What do you
> expect? This is how psy-rd works and I quote its author

I expected psy_rd have an effect on bitrate.

> "the human eye doesn't just want the image to look similar to the
> original, it wants the image to have similar complexity. Therefore, we
> would rather see a somewhat distorted but still detailed block than a
> non-distorted but completely blurred block. The result is a bias
> towards a detailed and/or grainy output image, a bit like xvid except
> that its actual detail rather than ugly blocking."

I think I understand now.  In order to have this "similar complexity" the
(total) bitrate is upped.  I thought that psy_rd does reallocate bits to
preserve detail (complexity?) where it is considered more important for the
human perception.

I read some forum posts and comments, which made me believe that psy_rd
contributes to a compression improvement.  Meaning that using it will either
allow you to use fewer bits to get the same quality (as human perception
goes) or better quality with the same bitrate.  So it appears the parm
controls (affects) how many bits are used without the promise of a better
compression.

I also run the experiments comparing psy_rd=0.0:0.0 to psy_rd=1.0:0.0.
Again, the second run featured the higher bitrate.

My confusion came from that I expected the encodings using psy_rd to have
*lower* bitrates.  (I was also suspicious when I got a quite large bitrate
impact from a quite small change: 0.0:0.0 -> 0.0:0.2.  But that can be
chalked up to my inexperience of the scaling of this particular parm value.)

Thanks.

> also gives them advantage in saving time. I personally, for SD
> encodes, always use 20 but am thinking to switch to 19, now that
> macroblock tree (MB tree) is part of x264 since it "somewhat"
> redefines CRF values yet again

I have encoded some OTA 1080i sources.  (Deinterlaced, denoised and scaled to
960:540 first and encoded with qp=0, then run the rest of the suite.)  The
original has some visible compression artifacts (broadcasing people if you
are listening, you need to update your hardware/software!!!).  I could not
tell the difference between crf=24 and crf=23.  (All artifacts I noticed were
in the original as well.)

So using 20 seems quite low to me.  Maybe crf values for larger pixelcount
should be naturally higher?  (I do not have SD sources encoded, I will do
some tests.)

Have a good day,
Matyas
-
Every hardware eventually breaks.  Every software eventually works.

-- 
Matyas
-
Every hardware eventually breaks.  Every software eventually works.