Creates a "boomerang" movie clip.

boomerang.zsh

#!/usr/bin/env zsh
set -ex

INPUT_FILE_PATH=${INPUT:a}
INPUT_DIR=${INPUT:a:h}
INPUT_EXT=${INPUT:e}

REVERSE_FILE_PATH="${INPUT_DIR}/reverse.${INPUT_EXT}"
FORWARD_FILE_PATH="${INPUT_DIR}/forward.${INPUT_EXT}"

BOOMERANG_FILE_PATH="${INPUT_FILE_PATH:r}.boomerang.${INPUT_EXT}"

ffmpeg -ss ${FROM} -y -to ${TO} -i "${INPUT_FILE_PATH}" -filter:v "setpts=PTS-STARTPTS" -vf reverse -af areverse "${REVERSE_FILE_PATH}"
ffmpeg -ss ${FROM} -y -to ${TO} -i "${INPUT_FILE_PATH}" -filter:v "setpts=PTS-STARTPTS"                          "${FORWARD_FILE_PATH}"

ffmpeg -y -f concat -safe 0 -i =(print "file '${FORWARD_FILE_PATH}'"; print "file '${REVERSE_FILE_PATH}'") -c copy "${BOOMERANG_FILE_PATH}"

rm -v "${REVERSE_FILE_PATH}" "${FORWARD_FILE_PATH}"

set +ex