Hi Lars.
You can try to solve it by adding this line to your style.css file.
.fluid-width-video-wrapper {padding-top: 56.25% !important;}
Unfortunately, I can’t suggest you a plugin to do what you need, I usually do things like that by my self. Anyway, I’m sure that with a fast search you’ll be able to find something; there are plugins for everything in WordPress 😉
