Thanks, but no luck. I tested it on a 3 second video, and got a 6 second video. I.e. it bounced 1 time, not 5 times.

Maybe this should be an AI reasoning test.

Here is what eventually worked, iirc (10 bounces):

  ffmpeg -i input.mkv -filter_complex "split=2[fwd][rev_in]; [rev_in]reverse[rev]; [fwd][rev]concat=n=2,split=10[p1][p2][p3][p4][p5][p6][p7][p8][p9][p10]; [p1][p2][p3][p4][p5][p6][p7][p8][p9][p10]concat=n=10[outv]" -map "[outv]" -an output.mkv