convert lsdvd output to chapters file for mkvtoolnix using bash and bc

lsdvd2chapters.sh

#!/usr/bin/env bash

#for nixos users:
#! /usr/bin/env nix-shell
#! nix-shell -i bash -p bash bc lsdvd

#lsdvd2chapters.sh: lsdvd wrapper for mkvtoolnix
#2021-07-11 08:00:00 GMT+2
#
#lsdvd2chapters.sh [input_dir] [output] [title]
#input_dir: path to VIDEO_TS. default: ./
#output: path to output file. default: stdout.
#title: which title we process. default: 01.
#
#Depends on bash, bc and lsdvd.
#Public Domain

#TODO: safely handle arguments, lsdvd etc edge cases.

dir=${1:-./}
out=${2:-/dev/stdout}
title=${3:-01}

sum=0
tab='	'
wtitle=""

while IFS=$'\ ' read -r -a myArray
do
	case "${myArray[0]}" in
		'Disc')
			echo Disc: "${myArray[2]}" 1>&2
		;;
		'Title:')
			wtitle="${myArray[1]%,}"
			echo Title: $wtitle 1>&2
		;;
		$tab'Chapter:')
			if [ "$title" = "$wtitle" ]; then
				sum="$(date -u -d "jan 1 1970 ${myArray[3]%,}" +"%s.%3N") + $sum"
				secs="$(echo $sum|bc)"
				floored=${secs%%.*}
				h=$(( floored / 3600 ))
				m=$(( ( floored / 60 ) % 60 ))
				s=$(( floored % 60 ))
				ns=${secs#"$floored."}

				echo -n CHAPTER"${myArray[1]%,}"=
				printf "%02d:%02d:%02d.%s\n" $h $m $s $ns
				echo CHAPTER"${myArray[1]%,}"NAME=
			#else
			fi
		;;
		*)
			#echo "${myArray[@]}"
			#echo "${myArray[0]}"
		;;
	esac
done < <(lsdvd -c "$dir" 2>/dev/null) > "$out"