[XviD-devel] problem

[Christoph Lampert]

On Fri, 4 Apr 2003, elcabesa wrote:

> i'm testing lot of stuff of xvid an i'm very happy about result=)
> the only oine problem/bug i found is that enabling qpel in fixed quant 
> encoding make psnr go down
> you cannot notice it in a cbr encoding couse bitrate saving  make xvid using 
> an  lower quantizer   so psnr raise =)

not always. Sometimes overall PSNR drops with QPel. Same for ffmpeg, btw.

http://rguyom.ath.cx/part7.html

> i don't know if it's a know effect of qpel, or if it's due to interpolation 
> reuested by standard

Yes, it's know and it depends heavily on the input material. But indeed,
often QPel has lower PSNR at also lower bitrate. 

gruel