Opened as a local file — inline video playback needs the page served over
http://, not file:// (this is a browser security
restriction, not something this page can work around). Videos will link out
to YouTube directly instead. To enable inline playback: open a terminal in
this folder and run python3 -m http.server, then visit
http://localhost:8000/ —
go to that exact file, not just the bare root URL, or your
browser may show whatever else is in that folder instead.