MediaMTX moves to v1.21.0 on the next software update (the installer and the update path share one pin). The config template's path hooks use the new upstream names; nothing else we set changed.
Upstream fixes that come with it — tighter browser-origin handling (Piston's listeners keep their explicit allow-all), sources with an empty password accepted again for older cameras, and an option to pause MediaMTX-side recording while a fallback slate plays.
