Cut files with ffmpeg lossless

actioncam.sh

#!/bin/bash
###
# [email protected] (2025-03-19)
# https://gist.github.com/90f21ebb14024c40ba46c16a0325a10d
###

set -euf -o pipefail

function errexit
{
	printf '%s: %s\n' "$(basename "$0")" "$*"
	exit 1
}

if [[ $# -lt 1 ]]
then
	printf 'Usage: %s FILENAME START END\n' "$(basename "$0")" >&2
	exit 1
fi

filename=$1
start=$2
end=$3

[[ -f "$filename" && -r "$filename" ]] || errexit "File not found or not readable!"
[[ "$start" =~ ^(([0-9]+:)?[0-9]+:)?[0-9]+$ ]] || errexit "Invalid start time format!"
[[ "$end" =~ ^(([0-9]+:)?[0-9]+:)?[0-9]+$ ]] || errexit "Invalid end time format!"

IFS=':' read -r -a astart <<< "$start"
starth=0; [[ ${#astart[@]} -gt 2 ]] && starth=$((10#${astart[-3]}))
startm=0; [[ ${#astart[@]} -gt 1 ]] && startm=$((10#${astart[-2]}))
starts=$((10#${astart[-1]}))
unset astart

IFS=':' read -r -a aend <<< "$end"
endh=0; [[ ${#aend[@]} -gt 2 ]] && endh=$((10#${aend[-3]}))
endm=0; [[ ${#aend[@]} -gt 1 ]] && endm=$((10#${aend[-2]}))
ends=$((10#${aend[-1]}))
unset aend

rend=$((endh * 3600 + endm * 60 + ends))
rstart=$((starth * 3600 + startm * 60 + starts))
[[ "$rend" -gt "$rstart" ]] || errexit "END <= START"
duration=$((rend - rstart))

dirname=$(dirname "$filename")
basename=$(basename "$filename")

if [[ "$filename" =~ [^0-9]*[0-9]{8}_[0-9]{6}\.[^.]+$ ]]
then
	IFS='_' read -r -a afile <<< "$basename"
	ftime=${afile[-1]}
	fdate=${afile[-2]}
	unset afile

	fdy=${fdate:0:4}
	fdm=${fdate:4:2}
	fdd=${fdate:6:2}
	unset fdate

	fth=${ftime:0:2}
	ftm=${ftime:2:2}
	fts=${ftime:4:2}
	unset ftime

	suffix=$(printf '.cut_%ds' "$duration")
	ext=$(sed -r 's/^.+\.([^.]+)$/\1/' <<< "$filename")
	prefix=$(sed -r 's/(.*)[0-9]{8}_[0-9]{6}\.[^.]+$/\1/' <<< "$basename")
	date=$(date -ud "$fdy-$fdm-$fdd $fth:$ftm:$fts UTC + $rstart seconds" +'%Y%m%d_%H%M%S')
	output=$(printf '%s/%s%s%s.%s' "$dirname" "$prefix" "$date" "$suffix" "$ext")
else
	suffix=$(printf '.cut_%d-%d' "$rstart" "$rend")
	output=$(sed -r 's/(\.[^.]+)$/'"$suffix"'\1/' <<< "$filename")
fi

[[ -e "$output" ]] && errexit "Output file already exists! ($(basename "$output"))"
ffmpeg -ss "${rstart}s" -to "${rend}s" -i "$filename" -c copy "$output"
exit $?