ffmpeg – Web overlay to video

everyone know Browser source from OBS. I’m looking for a similar routine which takes a web page and use it as an overlay while streaming using ffmpeg.

I have developed a web scoreboard which I use from the gym where I don’t have a PC with OBS. All I have is a 4G connection to internet to reach my server where I publish my rtmp stream taken from my mobile phone using Prism Live.

I’m in need to overlay the stream sent by my mobile phone (and other phones in the near future) with a web overlay as you can craft using OBS and Browser source. Any Idea?