@nprofile1q...As a user of Subsonic-compatible software, you'll probably want to look at the OpenSubsonic implementation of it, used by media servers like Navidrome. It improves on the API while staying backward-compatible. I can see why Bandcamp chose it as a reference for adding a streaming protocol to their music libraries, without reinventing the wheel. And being immediately compatible with existing Subsonic clients.
https://opensubsonic.netlify.app/No discovery or such though, this is the streaming bit