The server's `playable` flag is computed Chromium-first, but HEVC
web-playability is browser-dependent: WebKit (Safari on macOS/iOS) decodes
HEVC via the OS while Chromium/Firefox/Electron can't. Treating the flag as
global wrongly showed Safari users the download fallback for files they can
play inline.
The client now treats `playable === false` as "needs a capability check": it
pre-renders the fallback only when the current browser also can't decode the
format, gated on a one-time canPlayType probe (BROWSER_SUPPORTS_HEVC). Capable
browsers attempt inline playback; the <video> onError handler remains the
safety net for genuine failures.
Jannis Braun
0eb65b6608