How to write coding for video

Question

What is the coding to check whether the nested if statement is true or not?

        if (treeViewItem.IsSelected == true)
        {
            img3_a.Visibility = Visibility.Hidden;
            img3_b.Visibility = Visibility.Hidden;

            Video.Source = new Uri(@".\step_3.wmv", UriKind.Relative);
            Video.Play();

            descriptionText.Text = "1) Step 3.";

            ***if(video is being play)
            {
                MessageBox.Show("Video Played");
            }***
        }

Thanks.