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.