ffconcat

#!/bin/sh
help() { cat <</help
Concatenate given movies with ffmpeg, with chapters marking their original parts
Usage: ffconcat [OPTIONS] MOVIE1 MOVIE2... OUTPUT
  -F OPT, --ffmpeg Provide FFMPEG option (spaces will be lost, multiples okay)
  -n NAME, --name  Use NAME rather than the metadata title or filename.
                   You can use this multiple times to name each chapter.
                   The last one will be used for all remaining chapters.
  -q, --quiet      Show only warnings & errors. -qq: no warnings, -qqq: nothing

NAME may contain a few variables (sorry, no escape character is supported):
  %CHAPTER%  The chapter number
  %FILE%     The input file name (without path or extension)
  %MINUTES%  The chapter play time in minutes
  %SECONDS%  The chapter play time in seconds (total, not remaining)
  %TITLE%    The input file title (if title is missing/blank, this is %FILE%)

This uses the ffmpeg concat demuxer to concatenate movies without reencoding.
Each movie must have the same streams (codecs, dimensions, time base, etc).
See more at https://ffmpeg.org/ffmpeg-formats.html#concat

A part of media-scripts, https://github.com/adamhotep/media-scripts
ffconcat v0.4.20241105.0 copyright 2022+ by Adam Katz, GPLv2+
/help
}

usage() { help |grep -m1 ^Usage; }

# Information Separator 4 (non-printing ASCII code dec 28, oct \034, hex \x1c)
# is our field separator (AWK FS="field separator", ASCII FS="File Separator")
FS='\034'

die() { echo "$*" >&2; exit 2; }  # complain to STDERR and exit with error
needs_arg() { if [ -z "$OPTARG" ]; then die "No arg for --$OPT option"; fi; }

name=''
quiet=0
while getopts F:hn:qv-: OPT; do
  if [ "$OPT" = - ]; then # --option https://stackoverflow.com/a/28466267/519360
    OPT="${OPTARG%%=*}" OPTARG="${OPTARG#$OPT}" OPTARG="${OPTARG#=}"
  fi
  case "$OPT" in
    ( F | ffmpeg* )	needs_arg; ffmpeg_opts="$ffmpeg_opts $OPTARG" ;;
    ( h | help )	help; exit ;;
    # truncate at FS to prevent shenanigans. it's not printable anyway.
    ( n | name )	needs_arg; name="$name${name:+$FS}${OPTARG%%$FS*}" ;;
    ( q | quiet )	quiet=$((quiet+1)) ;;
    ( usage )		usage; exit ;;
    ( v | version )	help |tail -n1; exit ;;
    ( ??* )		die "Illegal option --$OPT" ;;  # bad long option
    ( ? )		exit 2 ;;  # bad short option (error handled by getopts)
  esac
done
shift $((OPTIND-1))

case $quiet in
  ( 0 )  quiet="" ;;
  ( 1 )  quiet="-loglevel warning" ;;
  ( 2 )  quiet="-loglevel fatal" ;;
  ( 3 )  quiet="-loglevel quiet" ;;
esac

# `command -v` only reliably handles one command. `type` implements AND.
if ! type ffmpeg ffprobe >/dev/null 2>&1; then
  die 'This script depends on ffmpeg and ffprobe. Please install ffmpeg.'
fi

if [ $# -lt 3 ]; then
  usage
  die "Try \`${0##*/} --help\` for more information."
fi

tmp="$(mktemp -d)"
trap "sleep 90; rm -rf $tmp" 0 1 2 5 9 11 15 18

output="$(eval echo '$'$#)"	# the final argument (yes, a safe eval call)
i=1

for file in "$@"; do
  if [ "$file" = "$output" ]; then break; fi	# the output is not also input

  if [ ! -r "$file" ]; then
    die "Cannot read '$file'"
  fi
  if [ ! -s "$file" ]; then
    die "Empty file: '$file'"
  fi

  movie="$tmp/$i.${file##*.}"	# preserve the extension but not the name
  # escaping logic for single quotes is odd, so just symlink the files instead
  ln -s "$PWD/$file" "$movie"
  echo "file '$movie'" >> "$tmp/list.txt"
  # show duration and (if present) tag title
  # then remove FS then convert newlines to RSes so this is one line long
  ffprobe -v error -show_entries format=duration \
                   -show_entries format_tags=title \
                   -of default=noprint_wrappers=1 \
                   "$movie" \
    |tr -d "$FS" |tr '\n' "$FS"
  # final (2nd or 3rd) item: filename without path or extension
  movie="${file##*/}"			# no path
  echo "FILE:title=${movie%.*}" 	# metadata label, no extension
  i=$((i+1))
done |awk -v FS="$FS" -v rate=1000000 -v name_str="$name" '
  BEGIN {
    print ";FFMETADATA1"
    if (name_str) { names_len = split(name_str, names, FS) } # make names array
  }
  NF {
    title = ""
    # ffprobe outputs in *stored* order. unreliable, but filename is always last
    for (f=1; f<=NF; f++) {
      if ($f ~ /^duration=/) { duration = substr($f, 10); continue }
      # if prospective title has a char that is not a dquote, quote, or space
      if (title == "" && $f ~ /^[^=]*title=.*[^"\047[:space:]]/) {
        title = $f
        sub(/^[^=]*=/, "", title)
      }
      if ($f ~ /^FILE:title=./) { filename = substr($f, 13) }
    }
    if (names_len) {
      if (NR >= names_len) { newtitle = names[names_len] }
      else { newtitle = names[NR] }
      gsub("%CHAPTER%", NR, newtitle)
      gsub("%FILE%", filename, newtitle)
      gsub("%MINUTES%", sprintf("%.0f", duration/60), newtitle)
      gsub("%SECONDS%", sprintf("%.0f", duration), newtitle)
      gsub("%TITLE%", title, newtitle)
      title = newtitle
    }
    else if (title == "") { title = "Chapter " NR }	# simple fail over
    # make colliding chapter names more informative by appending the chapter #
    else if (title_seen[title]++) { title = title "(" title_seen[title] ")" }

    printf "[CHAPTER]\nTIMEBASE=1/%d\nSTART=%.0f\n", rate, total
    total += duration * rate
    printf "END=%.0f\n", total - 1
    printf "title=%s\n\n", title
  }
' > "$tmp/metadata"

ffmpeg $quiet -analyzeduration 10000000 -probesize 10000000 \
      -f concat -safe 0 $ffmpeg_opts -i "$tmp/list.txt" -i "$tmp/metadata" \
      -map 0 -map_metadata 1 -map_chapters 1 -c copy "$output"