If there was a call for suggested ffmpeg effects, then heres one I have been having fun with. How practical or desirable it may be to include among the Cinelerra effects, I dont know. It is fast to run as an ffmpeg script from the command line.
ffmpeg -i $1 -i $1 -i $1 -i $1 -filter_complex [1:v]hflip; [2:v]vflip; [3:v]hflip,vflip; [0:v]hstack=inputs=2; hstack=inputs=2; vstack=inputs=2 -s 1280x720 -map $2ffmpeg -i $1 -i $1 -i $1 -i $1 -filter_complex [1:v]hflip; [2:v]vflip; [3:v]hflip,vflip; [0:v]hstack=inputs=2; hstack=inputs=2; vstack=inputs=2 -s 1280x720 -map $2The top script flips mirrors and stacks an input video to form a 2 x 2 mirror type kaleidoscope. The second script flips and mirrors 2 x 2 but inside out. If this was to become an F_kaleidoscope effect, then there may be an option switch needed between those two inverse results.
Ive brute force scaled at the output, it would clearly be better to divide by 2 at the input/inputs. Ive a similar pair of scripts to allow 4 different input videos to be thrown together. Just a suggestion, its very silly, I hope you find it of interest.