MP3 (MPEG-1/2 Audio Layer III) is the codec that made digital audio a consumer reality in the 1990s and remains everywhere by sheer momentum. It pioneered mainstream psychoacoustic compression — discarding masked detail — at bitrates from 128 to 320 kbps, good enough to fit albums on early players and stream over dial-up. For video soundtracks it has been superseded by AAC, which is more efficient and better at low bitrates, but MP3 still dominates podcasts, legacy music libraries, and anywhere maximum compatibility matters. Its core patents expired in 2017, so it is now effectively free to use, which only extends its long tail.
