“This theme does not support video headers”

Hi there!

I’m having a problem with my page.

I use a child theme of twenty seventeen, and i have installed a video header (which is working). But now i want to change the video, and it’s not working.

i click on customizer, and it opens, but the right side stays completely blank.
when i open the header section, it says my theme does not support video headers (which it clearly does, as i’m having one playing like a charm).

why is that, what can i do to fix it?

i would also be happy with a way to hardcode the video-url into my theme, as it is not going to be changed any more.
(i tried putting the wp-custom-header.js into my child theme and changing video.src, but it didn’t change anything).

I would be very happy if anyone could point me in the right direction, thanks