Adaptive Multi-Rate Audio
From Just Solve the File Format Problem
Adaptive Multi-Rate Audio is a narrowband audio compression format optimized for speech. AMR is a codec adopted by 3GPP and used by many mobile systems.[1][2][3] Apple iOS used the format for voice recordings and voicemail, but changed to the CAF in iOS 12.2[4]
See also AMR-WB
File Identification
The first 5 bytes of an AMR is the hex values 2321414D52 or ascii #!AMR
