This is *amazing*.
You can take an MP3 and encode it into MIDI. The results are horrifyingly mesmerising. Can you hear the vocal?
(Stolen from https://www.tumblr.com/red3blog/135098280942/formeldeharv-i-put-all-i-want-for-christmas-is )
Red No. 3

I'm driving myself up the wall because I swear I can hear the vocal line but I don't know how that could be if it was truly converted to MIDI. Unless you can replicate speech sounds entirely with mod…

Tumblr

@Edent So this is doing pitch-to-MIDI analysis? I kinda thought this would be a raw data to MIDI thing which would sound very, VERY weird.

On the other side, you can use tools to embed images in MP3s, as famously used in the soundtrack to the game FEZ. https://venturebeat.com/games/fez-hidden-images/

The Fez soundtrack’s hidden images and how they got there

The soundtrack to developer Polytron's Xbox Live Arcade-exclusive puzzle game Fez has only been out since Friday, but a group of industrious fans has already discovered a number of secret images hidden in individual music tracks.

VentureBeat