How to make an loading Screen window in qt

Question

I have an QT application that load some file but it take some time . I start the loading process in another thread but the problems is my background gui is freezed will the loading process is still ruing . I want to hide the main gui wile the thread is still running and another window with a loading git to appear in the meantime when the thread has finished the window to disappear and make the main gui reappear

Here is my code :

std::thread loading(&RecVideoReader::initTimeStempMap,&recvideo);

      QLabel *lbl = new QLabel;
      QMovie *movie = new QMovie("Gear-5s-200px.gif");
      lbl->setMovie(movie);
      lbl->show();
      movie->start();



      while(!recvideo.isMapInit()){
       this->hide();
      Sleep(1000);


  }this->show();
  loading.join();
  movie->stop();
  lbl->hide();