the problem with Apple devices aside (Videos are not showing up on public links, as known), now I also can't watch any stream on any other device because after clicking on "play" it says "No video with supported format and mime-type found"
When I watch the video on the dashboard, everything works. It also worked on Owncloud 8, I just installed (fresh) Owncloud 9 and this problem comes up. Any help appreciated!
Most likely this which gets fixed in the upcoming 9.1.1: