Video rotate-to-fullscreen uses IntersectionObserver to determine whether the video is sufficiently onscreen to qualify for rotate-to-fullscreen.

But IntersectionObserver doesn't take into account pinch zoom when determining visibility (i.e. it cares about being visible within the layout viewport, not the visible viewport).

So during pinch zoom, rotate-to-fullscreen can trigger even though the video is offscreen. This is less of a concern for mobile pages, but may be an issue for desktop pages.

(IIRC it's not currently possible for JavaScript to observe pinch zoom, so the current behaviour has the benefit of being exactly polyfillable by JS)

(technically affects all OSes with touchscreens, but in practice only relevant for Android)