Multithreaded Recursive FLAC dir -> Opus converter

flac_to_opus.rb

#!/usr/bin/env ruby
#
# Multithreaded Recursive FLAC dir -> Opus converter
# Destination dir tree is flat
#
# Example:
# flac_to_opus.rb music/ /media/3632-6166/MUSIC/
#

$bitrate = 180
$threads = 5
# you want to use a temp file if writing to a
# sd card to prevent lots of small writes
$usetempfile = true

class FlacToOpus

  def initialize(in_filename, out_filename)
    @finished = false
    @in_filename = in_filename
    @out_filename = out_filename
    @temp_filename = in_filename + ".opustemp"
    if $usetempfile == true
      if File.exists?(@out_filename)
        @finished = true
       end
    else
      @temp_filename = @out_filename
      if File.exists?(@out_filename)
        @finished = true
      end
    end
    if @finished == false
      puts "Encoding: " + @in_filename + " -> " + @out_filename    
      @thread = Thread.new { flac_to_opus(@in_filename, @temp_filename) }
    end
  end
  
  def finish
    return true if @finished
    @thread.join(0.05)
    if @thread.status == false or @thread.status == nil
      if $usetempfile == true
        `mv "#{@temp_filename}" "#{@out_filename}"`
      end
      return true
    end
    return false
  end

  def is_flac_file(filename)
    result = `metaflac --list "#{filename}" 2>&1`
    return !result.include?("ERROR")
  end

  def flac_to_opus(in_filename, out_filename)
    return if !is_flac_file(in_filename)

    flac_cmd = 'flac -scd "' + in_filename + '"'
    opusenc_cmd = "opusenc --quiet --bitrate=" + $bitrate.to_s + " "

    artist = `metaflac --show-tag=artist "#{in_filename}"`.chomp.sub("artist=","")
    title = `metaflac --show-tag=title "#{in_filename}"`.chomp.sub("title=","")
    if artist.length > 0
      opusenc_cmd += '--artist="' + artist + '" '
    end
    if title.length > 0
      opusenc_cmd += '--title="' + title + '" '
    end
	
    opusenc_cmd += ' - "' + out_filename + '"'
    cmd = flac_cmd + ' | ' + opusenc_cmd
    `#{cmd}`
  end
end

class FlacDirToOpusDir

 def initialize(in_dir, out_dir)
  @encoders = []
  Process.setpriority(Process::PRIO_PROCESS, 0, 15)
  flacdir_to_opusdir(in_dir, out_dir)
 end

 def flacdir_to_opusdir(in_dir, out_dir)
  if in_dir[0] != "/"
    in_dir = "./" + in_dir
  end
  if out_dir[0] != "/"
    out_dir = "./" + out_dir
  end	

  in_dir = File.absolute_path(in_dir)
  out_dir = File.absolute_path(out_dir)
  topdirname = File.basename(in_dir)
  out_dir_orig = out_dir	
  out_dir += "/" + topdirname

  puts in_dir + ' -> ' + out_dir

  Dir.foreach(in_dir) do |filename|
    next if filename == '.' or filename == '..' or filename == '-'
    if File.extname(filename) == ".flac"
      `mkdir -p "#{out_dir}"`
      while @encoders.length > $threads - 1
        @encoders.delete_if { |en| en.finish }
      end
      @encoders.push FlacToOpus.new(in_dir + "/" + filename, out_dir + "/" + File.basename(filename, ".flac") + ".opus")
    end
    if File.directory?(in_dir + "/" + filename)
      flacdir_to_opusdir(in_dir + "/" + filename, out_dir_orig)
    end
  end
 end

end

in_dir = ARGV[0]
out_dir = ARGV[1].chomp

if in_dir && out_dir
  FlacDirToOpusDir.new(in_dir, out_dir)
else
  puts "flac_to_opus [INDIR] [OUTDIR]"
end

If you have fd installed, a nice one-liner is:
fd -e flac -x opusenc --bitrate 128 {} {.}.opus

If you have fd installed, a nice one-liner is:
fd -e flac -x opusenc --bitrate 128 {} {.}.opus

That's impressive!