boomerang.sh

ffmpeg -i "$1" -r 14 -an -vf scale=1080:1920 -filter:v "setpts=0.5*PTS"  "$1.fr.mp4"
#exit;
ffmpeg -i "$1.fr.mp4" -r 30 -filter:v "setpts=0.5*PTS" "$1.rs.mp4"
ffmpeg -i "$1.rs.mp4" -filter_complex "[0:v]reverse,fifo[r];[0:v][r] concat=n=2:v=1 [v] " -map "[v]"  "$1.b.mp4"


for i in {1..4}; do printf "file '%s'\n" $1.b.mp4 >> list.$1.txt; done
ffmpeg -f concat -i list.$1.txt -c copy $1.boomerang.mp4

rm "$1.fr.mp4"
rm "$1.rs.mp4"
rm "$1.b.mp4"
rm "list.$1.txt"