I tried to recompile CinGG's version of ffmpeg with those plugins enabled:
FFMPEG_EXTRA_CFG="--enable-frei0r" (I have frei0r plugins 1.7.0 installed) and after tweaking /usr/share/cin/ffmpeg/plugin.opts (added frei0r filter_name=vignette at very end of it) I can see this plugin and even use some effects. But not sure where to find exact documentation for all those parameters?
Some are at (you have to scroll down to frei0r...)
Site seems to be
https://www.dyne.org/software/frei0r/
I liked the way they spelled -- Miscro$oft / Windoz