You can add a YouTube video to your
product detail pages by first going to the edit page for the Product
that you want to add video to.
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.