This is cool. Encode text data into audio. 170 characters, 2800 bps. You could send lightning invoices over ham radio! This is the app on my phone reading the audio from the YouTube video.

GitHub
GitHub - aicodix/rattlegram: Transceive UTF-8 text messages with up to 170 bytes over audio in about a second!
Transceive UTF-8 text messages with up to 170 bytes over audio in about a second! - aicodix/rattlegram