Let's assume we have a rooted Android OS on a device that supports Bluetooth. Can we build an app that advertises itself as a Bluetooth speaker via Bluetooth A2DP?
If that was possible, then any other device could pair / connect to our Bluetooth server app and stream any music / sound. This server app could then take the music stream and play it locally or even send it to other devices via Wi-Fi. This would theoretically enable a multi-room Bluetooth solution.
Any idea how to achieve this? Where would I start?
Turns out there is a very good and detailed answer to a related question here.
Short Answer: Possible, but requires to modify the Android OS configuration and quite some low level NDK development to expose the A2DP Sink role as API to be used.
Thanks @BartPlatak for the pointer!