Thumbnail.cs

 public async Task<BitmapImage> FetchThumbnail(StorageFile videofile)
        {
            //Fetching the thumbnail in form of StorageItemThumbnail
            var thumbnail = await videofile.GetThumbnailAsync(ThumbnailMode.VideosView);

            var inputBuffer = new Windows.Storage.Streams.Buffer(2048);
            
            IBuffer buf;
            IRandomAccessStream stream=new InMemoryRandomAccessStream();
                        
            while ((buf = (await thumbnail.ReadAsync(inputBuffer, inputBuffer.Capacity, InputStreamOptions.None))).Length > 0)
                await stream.WriteAsync(buf);

            var image = new BitmapImage();
            image.SetSource(stream);

            return image;
        }