first,u need to get the <embed> code
looks like this
<object width="640" height="385"><param name="movie" value="https://www.youtube.com/v/ZtfhD70eaS4&hl=en_US&fs=1&"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="https://www.youtube.com/v/ZtfhD70eaS4&hl=en_US&fs=1&" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="640" height="385"></embed></object>
u have to put that in between [ YOUTUBE]no space tho and they have to be capital letters[/ YOUTUBE]
hope i helped