 
 class MovieEditor
 {
-    var asset:AVAsset!
-    var insertClips:[CMTimeRange]!
+    private(set) var asset:AVAsset!
+    private(set) var insertClips:[CMTimeRange]!
     
     private var assetComposition:AVMutableComposition!
     private var transitionClips:[CMTimeRange]!

    }
    
    //MARK: push transition effect
    func push(srcTrack:AVMutableCompositionTrack, dstTrack:AVMutableCompositionTrack, range:CMTimeRange, direction:VideoTransitionDirection)->[AVMutableVideoCompositionLayerInstruction]
    {
        let size = srcTrack.naturalSize
        let center = CGAffineTransform.identity

    }
}

fileprivate enum VideoTransitionDirection
{
    case right, left, top, bottom
}
