You can’t change the down sampling factor after the filter has been initialised because it requires all the passes to be reinitialised.
I created a super dirty patch to fix this, that just calls initFilter in setDownSamplingFactor, this a very generic solution I have been using is some of my filters.
idk…changing down sampling is not really meant to be real time it’s just for convenience…and since it only can occurs occasionally re initializing the filter is not really an issue IMO.
I’ll review your patch.
EDIT : nvm…I misread the issue and the solution, I get it now… 
Well there are some real time useages btw.
If framerate < x reduce downsampling factor to ugly 
I committed the patch thanks.
sweet, thanks mate