There's https://en.wikipedia.org/wiki/Logitech_Media_Server https://en.wikipedia.org/wiki/Logitech_Media_Server . You can use a headless client called softsque

There's https://en.wikipedia.org/wiki/Logitech_Media_Server https://en.wikipedia.org/wiki/Logitech_Media_Server . You can use a headless client called softsqueeze (eg raspberry pi). The source media is actually streamed and the clients have to decode it. The protocol handles multi-room sync which I haven't seen elsewhere. There's also an abandoned implementation of the server in python (LMS is perl) on sourceforge somewhere.