func mergeVideosFilesWithUrl(savedVideoUrl: URL, newVideoUrl: URL, audioUrl:URL)
    {
        let savePathUrl : NSURL = NSURL(fileURLWithPath: NSHomeDirectory() + "/Documents/camRecordedVideo.mp4")
        do { // delete old video
            try FileManager.default.removeItem(at: savePathUrl as URL)
        } catch { print(error.localizedDescription) }

        var mutableVideoComposition : AVMutableVideoComposition = AVMutableVideoComposition()
        var mixComposition : AVMutableComposition = AVMutableComposition()

        let aNewVideoAsset : AVAsset = AVAsset(url: newVideoUrl)
        let asavedVideoAsset : AVAsset = AVAsset(url: savedVideoUrl)

        let aNewVideoTrack : AVAssetTrack = aNewVideoAsset.tracks(withMediaType: AVMediaType.video)[0]
        let aSavedVideoTrack : AVAssetTrack = asavedVideoAsset.tracks(withMediaType: AVMediaType.video)[0]

        let mutableCompositionNewVideoTrack : AVMutableCompositionTrack = mixComposition.addMutableTrack(withMediaType: AVMediaType.video, preferredTrackID: kCMPersistentTrackID_Invalid)!
        do{
            try mutableCompositionNewVideoTrack.insertTimeRange(CMTimeRangeMake(start: CMTime.zero, duration: aNewVideoAsset.duration), of: aNewVideoTrack, at: CMTime.zero)
        }catch {  print("Mutable Error") }

        let mutableCompositionSavedVideoTrack : AVMutableCompositionTrack = mixComposition.addMutableTrack(withMediaType: AVMediaType.video, preferredTrackID: kCMPersistentTrackID_Invalid)!
        do{
            try mutableCompositionSavedVideoTrack.insertTimeRange(CMTimeRangeMake(start: CMTime.zero, duration: asavedVideoAsset.duration), of: aSavedVideoTrack , at: CMTime.zero)
        }catch{ print("Mutable Error") }

        let mainInstruction = AVMutableVideoCompositionInstruction()
        mainInstruction.timeRange = CMTimeRangeMake(start: CMTime.zero, duration: CMTimeMaximum(aNewVideoAsset.duration, asavedVideoAsset.duration) )

        let newVideoLayerInstruction = AVMutableVideoCompositionLayerInstruction(assetTrack: mutableCompositionNewVideoTrack)
        let newScale : CGAffineTransform = CGAffineTransform.init(scaleX: 0.7, y: 0.7)
        let newMove : CGAffineTransform = CGAffineTransform.init(translationX: 230, y: 230)
        newVideoLayerInstruction.setTransform(newScale.concatenating(newMove), at: CMTime.zero)

        let savedVideoLayerInstruction = AVMutableVideoCompositionLayerInstruction(assetTrack: mutableCompositionSavedVideoTrack)
        let savedScale : CGAffineTransform = CGAffineTransform.init(scaleX: 1.2, y: 1.5)
        let savedMove : CGAffineTransform = CGAffineTransform.init(translationX: 0, y: 0)
        savedVideoLayerInstruction.setTransform(savedScale.concatenating(savedMove), at: CMTime.zero)

        mainInstruction.layerInstructions = [newVideoLayerInstruction, savedVideoLayerInstruction]


        mutableVideoComposition.instructions = [mainInstruction]
        mutableVideoComposition.frameDuration = CMTimeMake(value: 1, timescale: 30)
        mutableVideoComposition.renderSize = CGSize(width: 1240 , height: self.camPreview.frame.height)

        finalPath = savePathUrl.absoluteString
        let assetExport: AVAssetExportSession = AVAssetExportSession(asset: mixComposition, presetName: AVAssetExportPresetHighestQuality)!
        assetExport.videoComposition = mutableVideoComposition
        assetExport.outputFileType = AVFileType.mov

        assetExport.outputURL = savePathUrl as URL
        assetExport.shouldOptimizeForNetworkUse = true

        assetExport.exportAsynchronously { () -> Void in
            switch assetExport.status {

            case AVAssetExportSession.Status.completed:
                print("success")
            case  AVAssetExportSession.Status.failed:
                print("failed (assetExport.error)")
            case AVAssetExportSession.Status.cancelled:
                print("cancelled (assetExport.error)")
            default:
                print("complete")
            }
        }

    }