Lately I have been using avi4hv again to convert some other video trailers and had still the same annoying dithering problem (that increase the HAM fringing).
So I finally mailed to avi4hv author, TJ Edmister, to ask him how he could manage to render his sample videos without any dithering, and if there was any hidden DOS argument to activate/deactivate dithering that we would have missed.
As an answer, he has been very kind to make an updated version of avi4hv, which now has the so desired dithering option !
Well, here is what could be considered like TJ Christmas gift
And once again, a big thanks to TJ Edmister !