Adaptive Multi-Rate Audio

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. Apple iOS used the format for voice recordings and voicemail, but changed to the CAF in iOS 12.2

See also AMR-WB

File Identification
The first 5 bytes of an AMR is the hex values or ascii

Specifications

 * RFC 4867 RTP Payload Format and File Storage Format for the Adaptive Multi-Rate (AMR) and Adaptive Multi-Rate Wideband (AMR-WB)

Software

 * FFmpeg
 * SoX

Sample Files

 * AMR info and sample
 * Sample AMR
 * https://telparia.com/fileFormatSamples/audio/amr/