I can embed videos in content pages from Youtube as well - we do it in a Lesson activity during the Learn Moodle MOOC. Have you tried on one of the demo sites andc compared settings with your site - with a standard theme?
Lesson
Videos not embedding in Lesson Content page
Αυτή η συζήτηση κλειδώθηκε κι έτσι δεν μπορείτε να απαντήσετε σε αυτή.