Reverse a video for boomerang effect
useful tips
// scenario
Create an Instagram boomerang-style forward-reverse loop from a short clip.
// shell
$ ffmpeg -i input.mp4 -filter_complex "[0:v]split[fwd][rev];[rev]reverse[r];[fwd][r]concat=n=2:v=1:a=0,loop=3:size=999" output.mp4