         var compositionAudioTrack: AVMutableCompositionTrack!
         let videoTrack = videoAsset.tracks(withMediaType: AVMediaTypeVideo)[0] 
         
-        compositionVideoTrack = self.mixComposition.addMutableTrack(withMediaType: AVMediaTypeVideo, preferredTrackID: 0)
+        compositionVideoTrack = mixComposition.addMutableTrack(withMediaType: AVMediaTypeVideo, preferredTrackID: 0)
         do {
             try compositionVideoTrack.insertTimeRange(
                 CMTimeRange(start: kCMTimeZero, duration: videoAsset.duration),
                 of: videoTrack,
-                at: self.currentTimeDuration)
+                at: currentTimeDuration)
         } catch _ {
         }
         compositionVideoTrack.preferredTransform = videoTrack.preferredTransform
         
-        compositionAudioTrack = self.mixComposition.addMutableTrack(withMediaType: AVMediaTypeAudio, preferredTrackID: 0)
+        compositionAudioTrack = mixComposition.addMutableTrack(withMediaType: AVMediaTypeAudio, preferredTrackID: 0)
         do {
             try compositionAudioTrack.insertTimeRange(
                 CMTimeRange(start: kCMTimeZero, duration: videoAsset.duration),
                 of: videoAsset.tracks(withMediaType: AVMediaTypeAudio)[0] ,
-                at: self.currentTimeDuration)
+                at: currentTimeDuration)
         } catch _ {
         }
         
-        self.currentTimeDuration = self.mixComposition.duration
+        currentTimeDuration = mixComposition.duration
         
         // Add Layer Instruction
         let layerInstruction = AVMutableVideoCompositionLayerInstruction(assetTrack: compositionVideoTrack)
         
         // Hide
-        layerInstruction.setOpacity(0.0, at: self.currentTimeDuration)
-        self.layerInstructions.append(layerInstruction)
+        layerInstruction.setOpacity(0.0, at: currentTimeDuration)
+        layerInstructions.append(layerInstruction)
         
         return layerInstruction
     }

        layerInstruction.setTransform(scale.concatenating(transform), at: kCMTimeZero)
        
        // Hide
        layerInstruction.setOpacity(0.0, at: self.currentTimeDuration)
        self.layerInstructions.append(layerInstruction)
        
        return layerInstruction
    }

            } catch _ {
            }
        }
        return assetExportSession
    }
}
