Also I didn't know Google had patents for syncing audio across phones. I wonder if any of the mobile apps (like AmpMe [1]) have to pay some license fees.
I once spent an evening researching the different apps that could sync audio across multiple devices [2]. I also wanted to build my own app, so tried to see if it would be possible (only if you have a jailbroken phone.) I just wanted to play the same audio on two pairs of AirPods. I found out that the Samsung Galaxy S9 has a Dual Audio feature, and the iPhone X can theoretically support this with Bluetooth 5.0. And the AmpMe app can sync audio across multiple phones. (I was also really surprised to find out that they're a pretty huge company with 20 full time employees.)
[2] https://www.evernote.com/l/ACo7ItT-pItKkZoYf0YJy0raGhN5255FR...