I wanted to put a video on my website, but I wanted it to adapt to the viewer's bandwidth and screen (you know, how YouTube does, where you get the narrow 240p version if you're on a rubbish mobile connection, but you still get the video). After a bit of research, I worked out how (thank you to Scott Jehl about responsive video via CSS, and mux.com for HLS and ffmpeg instructions) and wrote a quick note in case anybody else needs the same.
https://www.kryogenix.org/days/2025/04/16/serving-streaming-video-that-adapts-to-bandwidth-from-your-own-website/