Embed is Broken

A user had said that firstly, he wishes to be able to embed stuff on mobile devices, but even on the desktop version iFrame embed won't show the video once he clicks "Post", only during edit you can see the first time. The embed code he sent me was. It will not display: http://technasium.userecho.com/topic/200104-what-do-you-think-of-this-hypnosis-headphones-suggested/ on mobile or desktop version.

<iframe width="420" height="315" src="//www.youtube.com/embed/maXrvHFHxJU?rel=0" frameborder="0" allowfullscreen></iframe>