audio/amr

The speech codec your GSM calls ran on, in a file: AMR compresses voice ferociously at rates down to 4.75 kbit/s, and the storage format RFC 4867 defines is what phones used for voice notes and MMS clips for a decade. It is a speech codec, not a music codec — everything outside the vocal band comes out underwater. The file layout is charmingly minimal: the ASCII header #!AMR followed by a newline, then raw frames, with no index, seeking tables, or metadata. RFC 4867 (2007) replaced the earlier RFC 3267 and also covers the wideband sibling audio/AMR-WB, whose header is #!AMR-WB.

Defined by RFC 4867 · IANA registration. Registry facts from the IANA media-types registry via mime-db.