We don't support video embedding in an email, because most email clients don't like it.
Instead, you should take a screenshot of the video and embed that, then make it a link to the YouTube page or a page on your site that has the video!
This works really well, and looks nice within your email too.
Wistia has a great post on why this works best for you and your reader/viewer:
http://wistia.com/blog/embedding-video-in-email