YouTube links play in YouTube's own player, so the video cannot be downloaded, and it plays only if its owner allows embedding. The chat still comes from your live_chat.json file, and it syncs to the YouTube player's time. It needs an internet connection. Subtitles from a file do not show on YouTube videos. Use a local file for offline playback and subtitles. For YouTube links, use the live site at higginsvision.francishigginsarchive.biz, hosted on GitHub Pages. A copy of index.html opened off disk is for local files.