split mp4 into individual files for each chapter

chapters.sh

#!/usr/bin/env bash

set -euo pipefail

#set -x

fail () {
  local error_message="$1"
  local exit_code=$2
  echo "$error_message" >&2
  exit "$exit_code"
}

check_dependency () {
  local cmd="$1"
  command -v "$cmd" > /dev/null || fail "Could not find required tools: please install $cmd" 2
}

check_dependencies () {
  check_dependency 'ffprobe' \
  && check_dependency 'jq'
}

check_file () {
  local f=$1
  if [[ ! -r $f ]]; then
    fail "Could not access $f"
  fi
}

list_chapters () {
  local cmd="-show_chapters"
  local target=$1
  ffprobe -print_format json -loglevel error ${cmd} -i "$target"
}

list_chapter_tuples () { 
  local target=$1
  list_chapters "$target" | jq -r ".chapters|.[]|.start_time,.end_time,.id,.tags.title" | tr -d '\r' |paste - - - -
}

extract_chapter () {
  local target=$1
  local output_dir="split_${target%.*}"
  local suffix="${target##*.}"
  local IFS=$'\t'
  read -r start end count title <<< "$2"
  mkdir -p "$output_dir"
  ffmpeg -i "${target}" -loglevel error -ss "$start" -to "$end" -c copy -map 0 "${output_dir}/${count}_${title}.${suffix}"
}

split_chapters () {
  local target=$1
  local IFS=$'\n'
  for tuple in $(list_chapter_tuples "$target"); do
    extract_chapter "$target" "${tuple}"
  done
}

main () {
  check_dependencies
  if [[ $# -ne 2 ]]; then
    fail "usage: $0 <video file> list|split" 3
  fi
  target=$1
  cmd=$2
  check_file "$target"

  if [[ $cmd == "list" ]]; then
    list_chapters "$target"
  elif [[ $cmd == "split" ]]; then
    split_chapters "$target"
  else
    fail "unrecognized command $cmd, valid options are list and split"
  fi
}

main "$@"