Create a boomerang loop
speed & reverse
// what it does
This uses -filter_complex to build a reversed copy of the video ([0:v]reverse[r]) and then concat=n=2:v=1:a=0 joins the forward clip and the reversed clip end-to-end into one video stream — a boomerang that plays forward then rewinds. v=1:a=0 tells concat to output one video stream and no audio.
// shell
$ ffmpeg -i input.mp4 -filter_complex "[0:v]reverse[r];[0:v][r]concat=n=2:v=1:a=0" output.mp4// gotcha
a=0 means the output is silent — audio is dropped entirely. Also, the last forward frame and the first reversed frame are identical, so it appears twice and causes a subtle stutter at the turnaround; trim one frame with trim/select if you need a seamless pivot.