extract srt from mkv container with ffmpeg (for synology)

mkv2srt-syno.sh

#!/bin/bash
# Extract subtitles from each MKV file in the given directory

# If no directory is given, work in local dir
if [ "$1" = "" ]; then
  DIR="."
else
  DIR="$1"
fi

# Get all the MKV files in this dir and its subdirs
find "$DIR" -type f -name '*.mkv' | while read filename
do
  # Find out which tracks contain the subtitles
  ffmpeg -i "$filename" |& grep 'subrip' | while read subline
  do
    echo $subline
    # Grep the number of the subtitle track
    tracknumber=`echo $subline |& egrep -o "[0-9]{1,2}:[0-9]{1,2}" | head -1`
    echo $tracknumber

    # Get base name for subtitle
    subtitlename=${filename%.*}
    echo $subtitlename

    # Extract the track to a .tmp file
    `ffmpeg -i "$filename" -vn -an -map $tracknumber -f srt "$subtitlename.srt.tmp" > /dev/null 2>&1`
    `chmod g+rw "$subtitlename.srt.tmp"`

    # Do a super-primitive language guess: ENGLISH
    langtest=`egrep -ic ' you | to | the ' "$subtitlename".srt.tmp`
    trimregex=""

    # Check if subtitle passes our language filter (10 or more matches)
    if [ $langtest -ge 10 ]; then
      `mv "$subtitlename.srt.tmp" "$subtitlename.en.srt"`
    else
      # Not our desired language: add a number to the filename and keep anyway, just in case
      `mv "$subtitlename.srt.tmp" "$subtitlename.$tracknumber.srt" > /dev/null 2>&1`
    fi
  done
done