title: Best approach to decode Youtube cipher signature using PHP or JS
body: <p>Youtube is using cipher signature for some of the videos when the <code>use_cipher_signature = true</code> in the dictionary returned through 
  <a href="http://www.youtube.com/get_video_info?&amp;video_id=Video_Id" rel="noreferrer">http://www.youtube.com/get_video_info?&amp;video_id=Video_Id</a></p>
  
  <p>Example id: _JQH3G0cCtY</p>
  
  <p>Ciphered signature is actually the scrambled signature which anybody can debug with few sets of working signatures. But Youtube keeps on changing the scrambling algo. 
  I have seen few Youtube video downloader which are working smoothly without being affected through this changing game. I think they are checking the player and extracting the decode script from the player file and hence it keeps them going.</p>
  
  <p>I need some help about the actual technique to use in this case. I am aware of 'youtube-dl' - a python program to download the videos. As I am not good in python, I think that they are using the same approach.</p>
  
  <p>Also there is a user-script JS file available here:
  <a href="http://userscripts.org/scripts/show/25105" rel="noreferrer">http://userscripts.org/scripts/show/25105</a> , which is doing the same thing. </p>
  
  <p>Any help about the sane approach to decode the cipher code in PHP or JS will be appreciated.</p>