title: AVCaptureSession with multiple previews
body: <p>I have an AVCaptureSession running with an AVCaptureVideoPreviewLayer.</p>
  
  <p>I can see the video so I know it's working.</p>
  
  <p>However, I'd like to have a collection view and in each cell add a preview layer so that each cell shows a preview of the video.</p>
  
  <p>If I try to pass the preview layer into the cell and add it as a subLayer then it removes the layer from the other cells so it only ever displays in one cell at a time.</p>
  
  <p>Is there another (better) way of doing this?</p>