class func compressVideo(_ inputURL: URL, outputURL: URL, handler:@escaping (_ session: AVAssetExportSession)-> Void){
        let urlAsset = AVURLAsset(url: inputURL, options: nil)

        let exportSession = AVAssetExportSession(asset: urlAsset, presetName: AVAssetExportPresetMediumQuality)

        exportSession!.outputURL = outputURL

        exportSession!.outputFileType = AVFileType.mp4

        exportSession!.shouldOptimizeForNetworkUse = true

        exportSession!.exportAsynchronously { () -> Void in
            handler(exportSession!)
        }
    }