title: Moving video background as mouse scrolls
body: <p>have you seen Katy Perry's website? It's awesome (I'm serious, no spamming)!</p>
  
  <p>It has a moving background video, and I can't figure out the way they implemented it.</p>
  
  <p>this is the homepage:</p>
  
  <p><a href="http://www.katyperry.com/" rel="nofollow">http://www.katyperry.com/</a></p>
  
  <p>and as you start to scroll down, the background image (in fact, video) starts playing.</p>
  
  <p>What I managed to figure out that this is the video itself, </p>
  
  <p><a href="http://www.katyperry.com/wp-content/themes/katyperry-2/library/video/KATY_BG_21.mp4" rel="nofollow">http://www.katyperry.com/wp-content/themes/katyperry-2/library/video/KATY_BG_21.mp4</a> </p>
  
  <p>and the vertical scrolling moves the video slider.</p>
  
  <p>I just can't seem to figure out how they do that, and it's driving me mad (spent a substantial amount of time trying to reverse engineer it)</p>
  
  <p>any ideas? have you done/seen anything like that before?</p>
  
  <p>Thanks in advance,
  Zsolt</p>