MiniDisc
From Just Solve the File Format Problem
MiniDisc is a discontinued CD-like audio disc developed by Sony. It was moderately successful in some countries, though not in the United States. While some pre-recorded MiniDiscs were produced, it was mainly used for home recording.
The recordable format is magneto-optical, while pre-recorded MiniDiscs are just optical.
It uses ATRAC or LPCM audio compression.