@Freemium User - Checkout my blog post on all the fixes we use to make sure background images work on the most amount of clients: http://www.emaildesignreview.com/html-email-coding/html-bulletproof-background-images-in-email-3850/
Hey Victoria - not my work, but I grabbed the code because I was curious. Hulu embedded a video to work within an email. Code: https://codepen.io/emailjay/pen/pxoOXV
From previous experience, you can have the youtube video show up in gmail by linking the image - it works like a pop up. But I don't know of a way to have a youtube video play directly in an email.
Hope this helps,
The other thing I've noticed is when using Windows 10 - converting pixels (px) to points (pt) solves it for a few issues, also making sure to set the height in the outlook conditional comment css styling. To convert from pixels to points - multiply by 0.75
640*0.75 = 480pt