unable to add video in folding box

Hello! I am trying to add a video in those boxes that unfold when you click them but, when I add it, it only plays sound without the image.

Do you know if it is possible to put a video there? Or what might be happening?

Here is the link to the page where we have the problem:

Arcadia

it is where it says "B-sides", now there is a link to the video, but I said I added the video and it whas black only playing the sound.