I've added YouTube embed code into my product description on one of my products and changed width/height so that it keeps the vertical format of the video. It looks perfect in the editing description preview, but when publishing, it seems that the theme is forcing the player to full width of the description area on the product page, which breaks my vertical width/height settings. It's almost as if this is being over-ridden by CSS somewhere that's deciding that the width should be X.
(And Merry Christmas!)
Share the URL of your stores, I'll help you out.