There’s an issue with the playback of Facebook videos in Safari. Same for macOS and iOS.
You can start videos but whenever you try to activate audio or want to stop playback, videos always restart from the beginning without sound since it’s disabled by default.
In short, you can neither activate audio nor stop the playback once it started.
It looks like some bug on Facebook side and it’s related to tracking.
It somehow works if I remove sandbox property from Facebook video iframe AND agree with Safari request to allow Facebook tracking. But it still reloads video after first click on “pause” (but works fine afterwards).
If Safari’s tracking request is not confirmed it reloads video every time (as it is now). So it’s a flaky solution.
I don’t want to allow Facebook (and other iframe) tracking and prefer to keep iframes sandboxed.
As a workaround you could try to use Firefox/Chrome or open video post page on a Facebook website.
That was my guess as well that it might be a conflict with tracking.
Currently I’m not actively using Safari but thought I might switch to it with the coming macOS upgrade, but it’s fine. I prefer your choice of preventing tracking.
Thank you for looking into it.