public async void Activate(FileOpenPickerActivatedEventArgs args)
{
_fileOpenPickerUI = args.FileOpenPickerUI;
_fileOpenPickerUI.FileRemoved += this.FilePickerUI_FileRemoved;
_fileOpenPickerUI.Title = "Select files from the video library";
QueryOptions qo = new QueryOptions();
var qr = KnownFolders.VideosLibrary.CreateFileQuery();
FileInformationFactory fif = new FileInformationFactory(qr, ThumbnailMode.VideosView);
lstView.ItemsSource = (await fif.GetFilesAsync());
Window.Current.Content = this;
Window.Current.Activate();
}