Extract and translate MKV subtitles

translate_subs.rb

#!/usr/bin/env ruby

# Ruby script to extract and translate subtitles from MKV files from English to Portuguese (but you can customize this)
#
# Dependencies:
#
#   1. `gem install srt`
#   2. `brew install translate-shell mkvtoolnix`
#
# Usage:
#
#   translate_subs.rb [FILE]
#
# Notice: it assumes the subtitles are on track index 3, which may change from file to file.
# Tracks can be checked using `mkvinfo file.mkv`

require 'shellwords'
require 'pathname'
require 'srt'

ARGV.each do |file|
  path = Pathname(file)

  en_srt = Shellwords.escape("#{path.basename('.*')}.en.srt")
  pt_srt = Shellwords.escape("#{path.basename('.*')}.srt")

  `mkvextract tracks #{Shellwords.escape(file)} 3:#{en_srt}`

  # Join split lines for better translation
  srt = SRT::File.parse(File.new(en_srt))
  total = srt.lines.size
  srt.lines.each_with_index do |l, idx|
    l.text = [`trans -no-warn -no-autocorrect -brief en:pt-BR #{Shellwords.escape(l.text.join(' '))}`.strip]
    printf("\r#{file} - %d%%", (idx + 1) * 100 / total)
  end
  printf("\r#{file} - %d%%", 100)
  puts
  IO.write(pt_srt, srt.to_s)

  `rm #{en_srt}`
end