[nynyny7]

As other commenters have pointed out, this is a C64 controlling an MP3 player.

People old enough to remember the late 1990s / early 2000s might recall that back then it was popular, too, to hook up an external MP3 decoder, e.g., to the parallel port; so that the PC's CPU would not be at 100% just for playing MP3 music.

[lokedhs]

Wait, was that popular? Now, I was mostly into the C64 and later Atari ST, with some insight into other platforms, but I don't think I've ever heard about an external MP3 decoder. On what's platform was this available?

The closest I can think of is the external clock chip for the Atari Falcon that allowed you to decode 44.1 kHz MP2.

[ElCapitanMarkla]

I do remember being about 12 and having to download music from Napster at a crap bitrate of 32kbps because our Pentium 100 struggled over that.