I'll try to put this in the FAQ a little later, but if you're website is running an SSL certificate, you need to tweak your definition slightly in order to fully support external embedding.
Find the source URL in your respective definitions'
Replacement HTML:
HTML Code:
src="http://www.youtube.com/embed/abc123456"
Add an
s.
Code:
src="https://www.youtube.com/embed/abc123456"
Of course, the respective website needs to actually provide
https URLs. Most do. A few don't. But relatively easy to check, and easy enough to tweak for your most used websites.