title: Youtube Encrypted signatures detected
body: <p>I'm researching video patterns, and for that i am required to download videos from youtube.
  I've found <a href="http://rg3.github.io/youtube-dl/" rel="nofollow">youtube-dl</a> project very useful for this exactly, as it is a command line tool written in Python (which integrates nicely with the rest of my project which is python on ubuntu based). </p>
  
  <p>Trying to download some videos, I have encountered this issue:</p>
  
  <pre><code>me@server:~/Desktop/YouTube/backend$ ./youtube-dl.py https://www.youtube.com/watch?v=8SbUC-UaAxE
  [youtube] Setting language
  [youtube] 8SbUC-UaAxE: Downloading video webpage
  [youtube] 8SbUC-UaAxE: Downloading video info webpage
  [youtube] 8SbUC-UaAxE: Extracting video information
  [youtube] 8SbUC-UaAxE: Encrypted signatures detected.
  ERROR: unable to download video
  </code></pre>
  
  <p>1) Is this because this video is copyright protected?<br> 
  2) Has anybody got experience downloading such videos? I see tools like <a href="http://www.freemake.com/free_video_downloader/" rel="nofollow">Free Video Downloader</a> and <a href="http://apps.conduit.com/musicapps-Music_Browser-app?appid=d5c4c431-a6ed-49fe-9670-df872dce43fe&amp;lang=he" rel="nofollow">this toolbar app</a> that seems to tackle this just fine. I need to accomplish similar functionality usable within a python web framework, nodejs or alike.</p>