Automatically extract subtitles using `ffmpeg` to work with Cast All The Things. Original author: https://github.com/EtienneM

catt-subtitles

#!/bin/bash

# set -x

print_usage() {
  echo "$0 [--map=0:3] video_file" >&2
  echo "" >&2
  echo "With video_file the path to a file like mkv which embeds the subtitles" >&2
  echo "--map: use the specified embedded subtitle." >&2
  echo "" >&2
  echo "Examples:" >&2
  echo "$0 --map=0:3 ./movie.mkv" >&2
}

map=""
while getopts ":-:" optchar; do
  [[ "${optchar}" == "-" ]] || continue
  case "${OPTARG}" in
    map=* )
      map=${OPTARG#*=}
      ;;
    help )
      print_usage
      exit -1
      ;;
  esac
done

# Remove from the list of arguments the one already handled by getopts
shift $(($OPTIND - 1))

if [[ $# -ne 1 ]]; then
  echo "Wrong number of argument" >&2
  print_usage
  exit -1
fi

which ffmpeg > /dev/null
if [[ $? -ne 0 ]]; then
  echo "You need to install ffmpeg (https://ffmpeg.org/download.html) to make use of this script."
  exit -1
fi
ffmpeg_cmd="ffmpeg -loglevel warning"

which catt > /dev/null
if [[ $? -ne 0 ]]; then
  echo "You need to install catt (https://github.com/skorokithakis/catt#installation) to make use of this script."
  exit -1
fi

if [[ -z "$map" ]]; then
  subtitles_count=$($ffmpeg_cmd -i "$1" 2>&1 | grep "Subtitle:" | wc -l)
  if [[ "$subtitles_count" -ne 1 ]]; then
    echo "There are more than one subtitle in the video file. Please specify the --map argument to this script." >&2
    echo "You can get the list of subtitles by executing the following command:" >&2
    echo "ffmpeg -i \"$1\" 2>&1 | grep \"Subtitle: \"" >&2
    exit -1
  else
    map=$($ffmpeg_cmd -i "$1" 2>&1 | grep "Subtitle:" | cut -d "#" -f2 | cut -d "(" -f1)
  fi
else
  ffmpeg -i "$1" 2>&1 | grep "Subtitle:" | grep $map > /dev/null
  if [[ $? -ne 0 ]]; then
    echo "Invalid map provided: $map"
    exit -1
  fi
fi

subtitles_file=$(mktemp --suffix=.srt --dry-run)

echo "Extract subtitle from the video file"
# From https://trac.ffmpeg.org/wiki/ExtractSubtitles
$ffmpeg_cmd -i "$1" -map "$map" -f webvtt "$subtitles_file"

echo "End of subtitle extraction, start to cast the video file"
catt cast --subtitles "$subtitles_file" "$1"