title: AVPlayerLayer: get rect of visible part of played video
body: <p><code>AVCaptureVideoPreviewLayer</code> has method <code>metadataOutputRectOfInterestForRect</code> which allows to calculate rectangle of visible (on the layer) part of the camera view <em>taking video gravity into account</em>.</p>
  
  <p>How this can be done for <code>AVPlayerLayer</code>?</p>