Oh this is really cool! Reminds me of ggwave [0].
It feels difficult to create hobbyist peripherals that interface with ones' phone -- trying to get cross-platform credentials to plug your own Arduino in via USB or connect via Bluetooth feels like a chore. I like the idea of phones communicating via some sort of audio library (ultrasonic maybe?) -- like R2-D2 chirping back and forth to communicate with other droids. I think this sort of thing could be part of a nice network of cross-device communication.
[0] - https://github.com/ggerganov/ggwave
Fun project. I tried encoding a short sample and the shareable m/#... URL plus WAV export makes it easy to reproduce and share specific payloads.
A feature that would make this even more useful as a debugging or teaching tool would be a decoder inspector: recovered bytes, framing errors, and maybe a small waterfall or discriminator view while decoding. For acoustic transfers especially, that would make it much easier to see whether a failure came from timing, levels, or just picking the wrong protocol.
That's actually a great idea. I will implement it this weekend! Thanks for the input.