Merge multiple mp4 files as chapters

mp4.sh

#! /usr/bin/env bash

####################################################
# Required Libraries
#
# library name | commands used   | verified version
# ------------------------------------------------
# ffmpeg       | ffmpeg/ffprobe  | 3.1.4 3.2
# gpac         | mp4box          | 0.6.1
# mp4v2        | mp4chaps        | 2.0.0
# coreutils    | grealpath/gdate | 8.25
# 
# Usage
# ./mp4.sh merge_as_chapter input*.mp4 output.mp4
#
####################################################
check_dependency(){
    echo "ffmpeg    $(echo_if $(program_is_installed ffmpeg))"
    echo "gpac      $(echo_if $(program_is_installed mp4box))"
    echo "mp4v2     $(echo_if $(program_is_installed mp4chaps))"
    echo "coreutils $(echo_if $(program_is_installed grealpath))"
}

# Merge multiple mp4 files as chapters
#   - Each input file name will be the chapter title
#   - Chapter markers in the input files will NOT be preserved
#   - Each input file must be extractly same format
merge_as_chapter(){
    echo "### Merge As Chapter ###"

    if [ "$#" -lt 2 ]; then
        echo "Error: Wrong number of parameters:"
        echo "Usage: merge_as_chapter input.mp4 [input.mp4...] output.mp4"
        return
    fi

    local output=${!#}
    set -- "${@:1:$# -1}"

    local chapterfile=$(printf "%s-%s" "/tmp/chapterfile" "$(basename ${output} .${output##*.})")

    merge_file "$@" "$output" &&
    create_chapterfile "$@" > "$chapterfile" &&
    add_chaptermark "$chapterfile" "$output"
}

# Merge multiple mp4 files
#   - Chapter markers in the input files will NOT be preserved
#   - Each input file must be extractly same format
merge_file(){
    echo "### Merge File ###"

    if [ "$#" -lt 2 ]; then
        echo "Usage: merge_file input.mp4 [input.mp4...] output.mp4"
        return
    fi

    local output=${!#}
    set -- "${@:1:$# -1}"

    echo "input :" "$@"
    echo "output:" "$output"

    ffmpeg -n -f concat -safe 0 -i <(create_filelist "$@") -c copy "$output"
}

add_chaptermark(){
    echo "### Add Chaptermark ###"

    if [ "$#" -ne 2 ]; then
        echo "Usage: add_chaptermark chapterfile file.mp4"
        return
    fi

    local chapterfile="$1"
    local input="$2"
    echo "chapterfile:" "$chapterfile"

    mp4box -chap "$chapterfile" "$input" &&
    mp4chaps --convert --chapter-qt "$input"
}

create_chapterfile(){
    echo "### Create Chapterfile ###"

    if [ "$#" -lt 1 ]; then
        echo "Usage: create_chapterfile input.mp4 [input.mp4...]"
        return
    fi

    local chapter_start=0
    local chapter_end=0
    for ((i=1; i<=$#; i++)); do
        file="${!i}"
        local chapter_name=$(basename "$file" .mp4)
        local chapter_number=$(printf "CHAPTER%s" "$i")
        local duration=$(duration "$file")

        printf "%s=%s\n" "$chapter_number" $(gdate -d@"$chapter_start" -u +%T.%3N) | tee -a /tmp/create_chapterfile.log
        printf "%sNAME=%s\n" "$chapter_number" "$chapter_name" | tee -a /tmp/create_chapterfile.log

        chapter_end=$(bc <<< "scale=6;$chapter_end+ $duration")
        chapter_start=$(bc <<< "scale=6;$chapter_end+ 0.001")
    done
}

create_filelist(){
    for file in "$@"; do
        printf "file %q\n" "$(grealpath "$file")" | tee -a /tmp/create_filelist.log
    done
}

duration(){
        ffprobe -v error -show_entries format=duration -of default=noprint_wrappers=1:nokey=1 "$1"
}


# ==============================================
# https://gist.github.com/JamieMason/4761049
# ==============================================
function program_is_installed {
  local return_=1
  type $1 >/dev/null 2>&1 || { local return_=0; }
  echo "$return_"
}

function echo_fail {
  printf "\e[31m✘ ${1}"
  echo -e "\033[0m"
}

function echo_pass {
  printf "\e[32m✔ ${1}"
  echo -e "\033[0m"
}

function echo_if {
  if [ $1 == 1 ]; then
    echo_pass $2
  else
    echo_fail $2
  fi
}

# ==============================================


# call arguments verbatim:
"$@"

Ubuntu 20.04 LTS:
line 79: mp4box -> MP4Box
line 99: gdate -> date
line 114: grealpath -> realpath
Since I couldn't find mp4v2/mp4v2-utils I followed lisamelton/video_transcoding#306 (comment) to get mp4chaps to work.
Thanks for the script 👍