Sorry for the late answer, I had other projects in the meantime.
The header seems okay:
HTTP/1.1 200 OK
Host: localhost:8081
Date: Thu, 08 Apr 2021 15:37:20 GMT
Connection: close
Content-Type: video/mp4
Content-Length: 1854608
I still haven’t found a solution to this problem.
It’s not only on localhost, but also on production.
I can’t even open the video link in Safari (getting a crossed-out play button).
It seems that the slider isn’t the problem. A normal Video (as popup) isn’t playing as well.
Is there a possibility to remove the media processing? Maybe it gets processed wrong.