Why does HTML5 video in Safari show a black screen instead of a video after loading?

Question

safari

I'm trying to embed a video stream in html5 video, with muted autoplay playisinline options, in chrome and firefox it works well as expected. But in safari, after the stream is playable and the poster is removed, I see a black screen instead of the video. Other browsers don't have this problem, of course. If you remove autoplay and manually call play (), this also does not help. The video only appears after I switch between tabs or between apps on macOS itself.