[tantalor]

And Benn encoded a bird into birdsong https://www.youtube.com/watch?v=hCQCP-5g5bo

[gaazoh]

And Disasterpeace encoded a puzzle in the Fez soundtrack: https://blog.krzyhau.pl/fez-spectrograms-adventure (and nobody has solved it in over a decade!)

Also, C418 put a creeper face in Minecraft's soundtrack.