private void StopButton_Click(object sender, RoutedEventArgs e)
 {
     MediaElement?.Stop();
 }
 private void ToggleFullscreen()
 {
     MediaElement?.ToggleFullscreen();
     Show();
     StartTimer();
 }
 private void ProgressSlider_ValueChanged(object sender, RangeBaseValueChangedEventArgs e)
 {
     MediaElement.SetPosition((float)(e.NewValue / ProgressSlider.Maximum));
 }