> Well, it's not self-playing but I found it amusing and wanted
> to share it anyway: https://youtu.be/wZCh4EY_kug 

Ah, but it _can_ be mechanical music.  It's on Thomas Sterk's 20-note
crank organ roll #38, "Leroy Anderson":

  Plink, plank, plunk!
  The Typewriter
  Bugler's holiday

http://www.thomas-sterk.nl/en/20-note-music-roll-nr-38 

You can hear it as Tim Wagner's 20-note "Bauchorgel" built by Der
Orgelbau in Wienerwald plays "The Typewriter":

https://www.youtube.com/watch?v=cG8hTiw6S6I 

Traditionally the concert piece features a desktop Underwood typewriter,
which weighs more than Tim's organ weighs, so he just adds the bell.

Wallace Venable