A multithreaded MP3 encoder built on LAME, using Robert Kausch’s SuperFast technique to run many libmp3lame instances in parallel and reassemble a single bit-reservoir-correct MP3 — roughly 8× faster than stock single-threaded LAME at the same quality.

It is also a small but fairly complete MP3 codec: encode, decode, wide input format support, high-quality resampling, and ID3 tagging.

github.com/MSIVST/SuperLAME
hydrogenaudio.org/index.php/topic,129699.0

References:

lame.sourceforge.io
github.com/enzo1982/superfast
en.wikipedia.org/wiki/ID3
en.wikipedia.org/wiki/MP3