I'm currently working hard on something to fill this void! I've made HomeHook v2 as a web app and HomeCast as an mpv interface installed on my HTPC and some Pis I have around the house!
I still need to document the installation procedure but if you're interested in playing stuff from Jellyfin and YouTube, feel free to send me a message and I'll see if I can help out!
I've just added images and more descriptions about each page of the web application in the GitHub readme. It should provide a nice overview now!