title: How to apply CoreImage filters to a video file efficiently?
body: <p>How to apply filters to a recorded video file ?</p>
  
  <p>I've go through the document of CoreImage, there are demos of how to apply filters to a still image, but no pre-recorded video file. Although I knew a video is a batch of still images, I could apply that to a each frame of the video. But I still want to know an efficient way to do that</p>
  
  <p>Any example(or instruments) of how to apply filter to a  video file?
  Thank you very much! This problem tortures me a lot .</p>