1997 my newton message pad had heriarchial menus and the OS automatically placed sound clips(very small 64bit 22.1khz ) into them according to date, time, file size and author. I was able to listen to these on my headphones. Yes, it wasn't meant to be a portable MP3 player but to me it worked well, and for my friends father who was a physician it worked even better. He had hundred of voice clips on his newton in heirarchial menus....
Oh, and about 2 years before I would always use my powerbook duo as a portable music player. In the apple menu not only did I have tons of nested songs files by author, genre, tv sound clips, movie sound clips, lecture notes... The OS automated the organization of these clips, and I was able create at that time the precursor to smartplaylist by the use of small Applescripts. I even remeber placing a couple of Apple commercials within the heirachial Apple menu.