Download video as mp3 from youtube

youdownloader.rb

#!/usr/bin/env ruby

require 'open-uri'
require 'cgi'

if ARGV[0].nil?
  puts "usage: #{$0} YOUTUBE_VIDEO_ID"
  puts "  sample: #{$0} wG6G4XBnvLQ"
  exit
end

link = "http://www.youtube.com/get_video_info?video_id=#{ARGV[0]}"
url = nil
info = open(link).read
info = CGI::parse(info)
title = info['title'][0]
info = info['url_encoded_fmt_stream_map'][0]
if info
  info.split(',').each do |info|
    info = CGI::parse(info)
    if info['type'][0].include?('video/mp4')
      url = "#{info['url'][0]}&signature=#{info['sig'][0]}"
      break
    end
  end
end

if url
  file = Tempfile.new(title)
  file_size = nil
  print 'Downloading video...'
  data = open(url, content_length_proc: -> (t) {
    file_size = t.to_f if t && t > 0
  }, progress_proc: -> (s) {
    if file_size
      p = ((100.0 * s) / file_size).round
      print "\b" * 80
      print "Downloading video: #{p}%"
    end
  })
  puts
  file.write(data.read)
  `ffmpeg -i '#{file.path}' -ab 128k '#{title}.mp3'`
  file.close
  file.unlink
else
  puts 'Can\'t download video!'
end