Change backgroundvideo to image on mobile


I have a background video as header. On mobile I would love to have an image as header background instead of a video, because I don’t want people to download the video if they have bad internet connection outside.

I don’t know how to do that. Can somebody please help me?
Thanks a lot!

Best Simon

Here is my site Read-Only: LINK
(how to share your site Read-Only link)