title: How to layer a distinct alpha channel animation on top of video?
body: <p>I'm developing an iphone app and am having issues with the AVFoundation API; I'm used to lots of image manipulation, and just kind of figured I would have access to an image buffer; but the video API is quite different.</p>
  
  <p>I want to take a 30 frame/sec animation which is generated as PNGs with transparency channel, and overlay it onto an arbitrary number of video clips composited inside of a AVMutableComposition.</p>
  
  <p>I figured that the AVMutableVideoComposition would be a good way to go about it; but as it turns out, the animation tool, AVVideoCompositionCoreAnimationTool, requires a special kind of CALayer animation. It supports an animation with basic stuff like a spatial transform, scaling, fading, etc -- but my animation is already complete as a series of PNGS.</p>
  
  <p>Is this possible with AVFoundation? If so, what is the recommended process?</p>