Below the video, click on "share", then click on "embed", then cut, come back here and paste. Done.
<object width="560" height="315"><param name="movie" value="//www.youtube.com/v/P1LNiD88690?version=3&hl=en_US"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="//www.youtube.com/v/P1LNiD88690?version=3&hl=en_US" type="application/x-shockwave-flash" width="560" height="315" allowscriptaccess="always" allowfullscreen="true"></embed></object>