How to download big videos ?

[OlostA777]

I would like to add a button in my app that can download the video just filmed. I use that code, but something is missing as it stops (it works perfectly for the little one or 2 seconds videos.

  @IBAction func onSavingBtnClicked(_ sender: Any) {
        let path = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true)[0]
         let originPath = path.appending("/\(lastFileName)")
       var test:Int = 0
      let alert = UIAlertView();
        alert.message = "Saving: \(lastFileName)";
        alert.addButton(withTitle: "Ok")
        alert.show()

        self.mCamera.downloadFile(fileName: lastFileName, destFilePath: originPath, success:
            {
                downloadTask in
                self.testLbl.text = String(describing: downloadTask.downloadedBytes)
        } , fail: {
            error in

            let alert = UIAlertView();
            alert.message = error as? String;
            alert.addButton(withTitle: "Ko")
            alert.show()
        }); 
        }
    }

Should I have to use URLSession ? But I don't really know how to use it. => I don't know how to use that:

 mCamera.urlSession(<#T##session: URLSession##URLSession#>, downloadTask: downloadTask, didWriteData: downloadTask.downloadedBytes, totalBytesWritten: downloadTask.downloadedBytes, totalBytesExpectedToWrite: downloadTask.totalBytes)
//

Thanks in advance.