openfest/2023/video/offset.sh

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#!/bin/bash
set -euo pipefail
function msg {
echo "${@}" >&2
}
function die {
msg "${@}"
exit 1
}
if [[ $# -ne 3 ]]; then
die "usage: ${0} <input> <output> <offset>"
fi
input="${1}"
output="${2}"
offset="${3}"
if [[ ! -f "${input}" ]]; then
die "input file ${input} does not exist"
fi
if [[ -e "${output}" ]]; then
die "output file ${output} already exists"
fi
ffmpeg -i "${input}" -itsoffset "${offset}" -i "${input}" -map 1:v -map 0:a -c copy "${output}"