title: iOS: drawViewHierarchyInRect:afterScreenUpdates: doesn't draw a AVPlayerLayer content
body: <p>I tried to take a snapshot of a <code>UIView</code> which contains an <code>AVPlayerLayer</code>, however the video part was drawn black. On the other hand, when I use <code>resizableSnapshotViewFromRect:afterScreenUpdates:withCapInsets:</code> then the resulting view contains the video snapshot correctly. However, I cannot get an image out of it, so I'm stuck with <code>UIView</code> instead of <code>UIImage</code>.</p>
  
  <p>I thought that unlike <code>renderInContex</code>, <code>drawViewHierarchyInRect</code> should capture all the "special" OpenGL and video layers also. Is this not possible?</p>