rename_m4a.rb

require 'rubygems'
require 'mp4info'
require 'fileutils'

def padded_track_num(num)
  num <= 9 ? "0#{num}" : "#{num}"
end

print "Enter directory: "
dir = gets.chomp
full_path_dir = File.expand_path(dir)
Dir.foreach(full_path_dir) do |filename|
  if File.extname(filename) == '.m4a'
    full_path_filename = File.join(full_path_dir, filename)
    File.open(full_path_filename) do |file|
      mp4 = MP4Info.new(file)
      filename_with_track = "#{padded_track_num(mp4.TRKN.first)} #{filename}"
      full_path_filename_with_track = File.join(full_path_dir, filename_with_track)
      FileUtils.mv(full_path_filename, full_path_filename_with_track)
    end
  end
end