add_subs.rb

#! /usr/bin/env ruby
require 'logger'
require 'shellwords'

files = Dir.glob('*.srt') - ARGV
logger = Logger.new(STDOUT)

def shell_quote(string)
  return '' if string.nil?
  string = string.to_s if string.respond_to? :to_s
  if string.empty?
    "''"
  else
    string.split("'", -1).map { |m| "'#{m}'" }.join("\\'")
  end
end

ARGV.each do |f|
  begin
    basename = File.basename(f, '.*')
    ext = File.extname(f)
    newname = f.gsub(/#{ext}$/i, ".subbed#{ext}")
    subs = files.select do |x|
      x =~ /#{basename}[_\.].{3}\.srt/i
    end

    subs = subs.uniq.sort

    # Promote english
    eng_index =  subs.find_index { |x| x.match(/eng/) }
    subs.unshift(subs.delete_at(eng_index)) unless eng_index.nil?

    inputs = []
    languages = []
    subs.each do |s|
      lang = s.match(/.*[_\.](.{3})\.srt\z/)[1]
      inputs << shell_quote(s)
      languages << shell_quote(lang)
    end

    args = ['-i', shell_quote(f)]

    # Add inputs
    args += inputs.flat_map do |i|
      ['-i', i]
    end

    # Map Statements
    args += Array.new(inputs.count + 1) do |i|
      ['-map', i.to_s]
    end.flatten

    # Inject copy mode

    args += ['-c', 'copy']

    # Metadata
    args += languages.flat_map.with_index do |l, i|
      ["-metadata:s:s:#{i}", "language=#{l}"]
    end

    # Add final name
    args << shell_quote(newname)

    options = args.join(' ')
    logger.debug "ffmpeg #{options}"
    IO.popen("ffmpeg #{options}", 'r') do |pipe|
      logger.debug pipe.read
    end
  end
end

convert.rb

#! /usr/bin/env ruby
require 'logger'
require 'shellwords'

logger = Logger.new(STDOUT)
def shell_quote(string)
  return '' if string.nil?
  string = string.to_s if string.respond_to? :to_s
  if string.empty?
    "''"
  else
    string.split("'", -1).map { |m| "'#{m}'" }.join("\\'")
  end
end

ARGV.each do |f|
  begin
    ext = File.extname(f)
    newname = f.gsub(/#{ext}$/i, '.x265.mkv')
    input = shell_quote(f)
    output = shell_quote(newname)

    command = ['ffmpeg', '-y', '-i', input, '-c:v', 'libx265', '-c:a', 'copy', '-c:s', 'copy', output].join(' ')
    logger.debug(command)
    IO.popen(command, 'r') do |pipe|
      logger.debug pipe.read
    end
  rescue
    next
  end
end