title: Is it possible to use both CIFilter and GPUImage filter on AVMutableComposition?
body: <p>I have an AVMutableComposition with two tracks (one for video and audio each) that combines multiple videos (as segments: <code>AVCompositionTrackSegment</code>) for playback. I have to apply filters on selected videos and not on the whole composition (lets say on 2nd and 4th segment when I have total 4 segments). For example if user selects to apply a filter on video 2 then I apply that filter for the respective duration of composition using <code>AVMutableVideoComposition(asset: AVAsset, applyingCIFiltersWithHandler: (AVAsynchronousCIImageFilteringRequest) -&gt; Void)</code>. It is working fine. </p>
  
  <p>Now I want to use some custom filters, created using <code>GPUImage</code> library. So my question is does <code>GPUImage</code> has an API to apply filters on a selected segment or for a specific duration of <code>AVMutableComposition</code>? So that I can use both <code>CIFilter</code> for built-in and <code>GPUImage</code> for custom filters. </p>