It seems that Safari (desktop and iOS) is not respecting the Cache-Control header for video files like video/mp4 and video/webm.
The response headers for the video includes
Cache-Control: public, max-age=3600
And the response comes from the network any time the page is refreshed.
I've checked that the Disable Cache is not enabled in dev tools.
The same video request is cached as expected on Chrome and Firefox.