tl;dr: The author ported ULC (Ultra Low Complexity Codec), an obscure MP3-like transform codec originally designed for Game Boy Advance, to the Nintendo 64 by offloading the IMDCT to the RSP coprocessor using 16-bit fixed point math. The result delivers 44100 Hz stereo audio at near-Opus bitrates using only ~4% CPU and ~5% RSP time, making it viable for in-game music and speech. It's already been merged into Libdragon and used in a recent N64 port of Half-Life to fit 2,500 sounds and 27 music tracks on a 64MB cartridge.