it is the same for us as well, i compared working youtube video to one i just tried to see the code difference
<iframe
width="420" height="315" src="
http://www.youtube.com/embed/_iQRXuAo6Eg"
frameborder="0" allowfullscreen></iframe>
the above
code works fine but the new ones are missing the http: which is why they
dont work, i added the http: to the above code and got it working,
this is the code youtube now give
<iframe
width="420" height="315" src="//
www.youtube.com/embed/_iQRXuAo6Eg"
frameborder="0" allowfullscreen></iframe>
you can see the http: is missing, this is the only way i can get youtube video to work now is by adding it