Merge multiple files with chapters using ffmpeg

ffmerge.sh

#!/usr/bin/env bash
# Usage: FFMETADATA=/path/to/metadata FFOUTPUT="My Output File.mp4" ./ffmerge.sh /path/to/*.wav
set -eo pipefail
# arguments required
if [ $# -eq 0 ]
then
  >&2 echo "one or more files required"
  exit 1
fi
filelist=$(mktemp)
audio=$(mktemp)
files=()
FFMETADATA="${FFMETADATA:?Missing FFMETADATA}"
FFOUTPUT="${FFOUTPUT:?Missing FFOUTPUT}"
while [ -f "$1" ]
do
  outfile=$(mktemp)
  # add file to array
  files+=($outfile)
  # extract audio to wav file
  ffmpeg -y -i "$1" -vn -c:a copy -f wav "$outfile"
  # build file list
  echo "file '$outfile'" >> "$filelist"
  # remove this file from the argument list
  shift 1
done
# combine audio files
ffmpeg -y -f concat -safe 0 -i "$filelist" -c copy -f mp4 "$audio"
# combine audio and chapters
ffmpeg -y -i "$audio" -i "$FFMETADATA" -map_metadata 1 -c:a copy "$FFOUTPUT"
# clean up
rm -v $filelist $audio ${files[@]}