À propos des fichiers AMR

AMR (AMR Audio · Format audio)

Lancement 1999 Par 3GPP (Ericsson, Nokia)

AMR Audio (.amr) est un format de fichier pris en charge par KaijuConverter pour l’archivage, l’échange professionnel et la conversion multiplateforme.

Famille

Audio Files

Extension

.amr

Type MIME

audio/amr

Utilisable comme

Entrée Sortie

L'histoire

COMMENT AMR
A VU LE JOUR.

AMR — Adaptive Multi-Rate — was standardized by 3GPP in 1999 as the voice codec for 3G mobile networks (UMTS). Before AMR, GSM used a fixed 13 kbps codec that sounded awful but saved bandwidth. AMR’s trick was adaptive bitrate: when signal was strong, the phone would encode voice at 12.2 kbps; as conditions degraded, it would drop to 4.75 kbps, sacrificing audio to keep the call connected.

For 15 years almost every cellphone call in the world used AMR. Multimedia messages (MMS) and voicemail recordings also stored their audio as .amr files. The format is still active in 2G/3G networks and legacy voicemail systems but has been superseded in LTE/VoLTE by AMR-WB and Enhanced Voice Services (EVS). A .amr file is almost always a recorded voicemail or an old phone memo.

CURIOSITÉS ET
ANECDOTES.

Almost every 3G cellphone call between 2000 and 2015 used AMR as the voice codec — billions of calls per day.

AMR can switch between 8 bitrates (4.75 to 12.2 kbps) on the fly as cell signal fluctuates.

The 3GPP extended AMR to AMR-WB (wideband) in 2001, adopted by most LTE/VoLTE networks.

Android phones recorded voice memos as .amr files by default until around 2014.

Despite its limited bandwidth, AMR sounds clear enough for speech — the codec is speech-optimized, not music-capable.

POINTS FORTS ET
LIMITES.

Points forts

Extremely low bitrate — 4.75-12.2 kbps for speech.
Designed for error-prone mobile channels — handles packet loss gracefully.
Tiny file sizes — hours of voice in a few MB.
Mandatory codec in all 3G/UMTS phones — universal cellular compatibility.

Limites

Speech-only — music sounds distorted.
Narrowband (8 kHz sample rate) — muffled compared to modern codecs.
Patent-encumbered until recently — licensing fees slowed adoption outside telephony.
Being phased out of new devices in favor of EVS and Opus.
Non-standard extensions and variants make tooling inconsistent.

Tailles et poids typiques

1-min voice memo

45-90 KB

1-hour voicemail archive

3-5 MB

Spécifications techniques

MIME type: audio/amr
Extensions: .amr, .3ga
Standard: 3GPP TS 26.071 (narrowband), TS 26.171 (wideband)
Sample rate: 8 kHz (AMR-NB); 16 kHz (AMR-WB)
Bitrates: 4.75, 5.15, 5.9, 6.7, 7.4, 7.95, 10.2, 12.2 kbps

CONVERTIR DEPUIS
AMR

amr mp3 amr wav amr flac amr aac amr m4a amr ogg amr opus amr wma amr aiff

CONVERTIR EN
AMR

mp3 amr wav amr flac amr aac amr ogg amr opus amr m4a amr

Cas d'usage courants

Voice recordings, phone calls