I would have your friend stream to Broadcast Box. You can run it on the Raspberry Pi!

Then I would pull that source into your OBS. You have two options

* Pull Broadcast Box as a browser source

* Use my PR that adds WHEP Sources https://github.com/obsproject/obs-studio/pull/10353

For now I would do Browser Source (is easier/no custom builds). In the future when WHEP is merged that is the way to go. If you get stuck jump in the Discord and happy to help debug! https://discord.gg/An5jjhNUE3