First. click on the SHARE link under the video in youtube.
Second. copy the link.
Third. reply to or begin a thread.
Fourth. click on the ladder icon above the advanced text box
(it looks exactly like the first one in the pic below).
Fifth. past the link you copied and click on 'OK'.
You'll also need to add 10 letters of text minimum.
Sixth. Post. That will show the video image instead of just a link.