You might find this an interesting read (PDF):   
<a href="http:&#x2F;&#x2F;infoscience.epfl.ch&#x2F;record&#x2F;200925&#x2F;files&#x2F;article-vp9-submited-v2.pdf" rel="nofollow">http:&#x2F;&#x2F;infoscience.epfl.ch&#x2F;record&#x2F;200925&#x2F;files&#x2F;article-vp9-s...</a>