Next, find the long description rich text editor and click "source" as shown in screenshot.
Code for the video replace the highlighted area with your youtube video url
<iframe allowfullscreen="" frameborder="0" height="315" src="http://www.youtube.com/embed/AmRTQAHDg" width="420"></iframe></div>
Done. Now your You Tube video player will be embedded directly within the product detail description.