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.^[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

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
• dexvert samples — audio/amr

References

1. ↑ https://en.wikipedia.org/wiki/Adaptive_Multi-Rate_audio_codec
2. ↑ http://www.voiceage.com/AMR-NB.AMR.html
3. ↑ https://tools.ietf.org/html/rfc4867
4. ↑ https://www.macrumors.com/2019/03/13/ios-12-2-improved-audio-message-quality/