audio/aac

Raw AAC in an ADTS transport stream — the codec without the MP4 wrapper, registered surprisingly late in 2018 against ISO/IEC 14496-3. Use it only for bare .aac streams; the AAC everyone actually listens to lives inside MP4 containers and is audio/mp4, a distinction servers get wrong constantly. There is no signature entry here because ADTS frames start with a 12-bit syncword (fff plus flag bits), so the second byte varies and no clean byte sequence at a fixed offset identifies the format.

.aac means ADTS framing; .adts is the explicit but rarely used alternative.

Defined by IANA registration — audio/aac · IANA registration. Registry facts from the IANA media-types registry via mime-db.