Xvid encodings and nvop

Hi, I'm actually seeing that xvid_encraw provides useful global informations about produced frames 
in a brief summary.
Now, the informations it prints differ from those detected by mpeg4modifier (both in the gui version 
and in the cli version), the point is nvop usage: often xvid_encraw reports they were written, yet 
mpeg4modifier doesn't detect them.
Now I wonder: which is right? (I don't trust gspot 'cause it seems to be abandonware)
And then I ask: how can I set an encoding in order to be sure nvops will get written? And how to set 
it in order they won't?
Thank you
Elio