I am not sure how it was possible, but I was able to play mp3s on my 386sx 16mhz (with turbo button) using the mpg123 player. OS was Slackware Linux.
Sure that was a regular bitrate stereo mp3? I remember struggling a lot with my 486DX/100, waiting for better assembly optimization to happen on Linux (to keep up with a DOS mp3 player that handled it better).
I no longer have the details, but the music was just some mp3 files I copied from friends. Buffering may have played a role as I had at some point, I had maxed out the specs memory-wise.
There was also a time when my computer playing mp3 in winamp while trying to browse the web would glitch the music due to buffer underun. Then I guess faster computers came along...
That is actually the original reason I switched to Linux in the late 90's. I couldn't multitask while listening to music in winamp while I could still browse and use staroffice while playing music on mpg123 on that old, already considered obsolete, computer I was using at the time.