title: How to trigger redraw of filter in AVVideoComposition's applyingCIFiltersWithHandler?
body: <p>I'm using Swift to show content from an AVPlayer in a view's AVPlayerLayer. The associated AVPlayerItem has a videoComposition, and slightly simplified version of the code to create it (without error checking, etc.) looks like this:</p>
  
  <pre><code>playerItem.videoComposition = AVVideoComposition(asset: someAsset, applyingCIFiltersWithHandler: {
                  [unowned self] (request: AVAsynchronousCIImageFilteringRequest) in
  
      let paramDict = &lt;&lt; set up parameter dictionary based on class vars &gt;&gt;
  
      // filter the image
      let filter = self.ciFilterWithParamDict(paramDict) {
      filter.setValue(request.sourceImage, forKey: kCIInputImageKey)
      if let filteredImage = filter.outputImage {
          request.finishWithImage(filteredImage, context: nil)
      }
  })
  </code></pre>
  
  <p>This all works as expected when the AVPlayer is playing or seeking. And if a new videoComposition is created and loaded, the AVPlayerLayer is rendered correctly.</p>
  
  <p>I have not found a way, however, to "trigger" the AVPlayer/ AVPlayerItem/ AVVideoComposition to re-render when I have changed some of the values that I use to calculate filter parameters. If I change values and then play or seek, it is rendered correctly, but only if I play or seek. Is there no way to trigger a rendering "in place"?</p>