Can anyone recommend a good open source software that allows you to cast using all the popular protocols to an rpi? Feels like the "smart" part of these smart speakers and devices seems to be what dies first. I've got a 4 year old pioneer receiver that has built in Chromecast and it simply stopped working (likely deprecated API/sdk) with no updates to fix it. Likewise there's tons of great amplifiers and receivers/speakers out there that could easily be updated to support modern streaming and speaker aggregation with minimal e-waste.
My favorite "smart" speaker in the house is a very old (~20 years) Altec Lansing 2.1 speaker kit that has a (sadly now discontinued) Chromecast audio plugged into it's headphone in.
If you end up looking for a product that does this rather than building it yourself, I've had a good experience with the WiiM Mini: https://wiimhome.com/wiimmini/overview
My favorite "smart" speaker in the house is a very old (~20 years) Altec Lansing 2.1 speaker kit that has a (sadly now discontinued) Chromecast audio plugged into it's headphone in.
Edit: found this which looks to fit the bill - https://github.com/balena-io-experimental/balena-sound