Full Size Video - too small

Hi, I have a problem with the showing of the full size video on my website. It's shown to narrow, it's actually only have of it that is shown. Does it have to do with the initial size of the video, or what else could be done wrong? finde-academic.de
Thanks!

Add a logo as shown in description and it works.

<img style="margin:50px 0" src="images/logo.png" width="200" height="50" alt="logo" />

And you need to add a slider to the headerbar module position and then you can see the video.
The video is based on fullscreen background and the content is an overlay.