Sobre os arquivos AMR
Áudio AMR
Formato Adaptive Multi-Rate desenvolvido pela 3GPP para voz em celulares 3G. Usado em gravações de mensagens de voz mobile dos anos 2000. Substituído por Opus em apps modernas.
Família
Audio Files
Extensão
.amr
Tipo MIME
audio/amr
Pode ser usado como
COMO NASCEU O
FORMATO AMR.
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 The format is still active in 2G/3G networks and legacy voicemail systems but has been superseded in LTE/VoLTE by AMR-WB and Enhanced Voice Services (EVS).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.
CURIOSIDADES E
FATOS INTERESSANTES.
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.
VANTAGENS E
LIMITAÇÕES.
Vantagens
- 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.
Limitações
- 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.
Tamanhos típicos de arquivo
1-min voice memo
45-90 KB
1-hour voicemail archive
3-5 MB
Especificações técnicas
- 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
CONVERTER A PARTIR DE
AMR
Casos de uso comuns
Voice recordings, phone calls
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AMR vs M4A
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AMR vs OGG
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Conversões populares de AMR
Os destinos mais procurados ao converter arquivos AMR.
Perguntas frequentes sobre AMR
Perguntas frequentes
AMR (AMR Audio) is an audio formatoo de arquivo used to store sound recordings — music, voice, podcasts, sound effects. The formato defines how the audio samples are comprimido (or stored raw), what bitrates are suportado, e how metadata como title, artist, album, e cover art is embedded. It is part of the audio arquivos family.
VLC, foobar2000, e the default media players no Windows e macOS handle AMR natively. On mobile, iOS Music e Android media apps vary in their support — popular formatoos funcionar everywhere; niche ones may need a dedicated app. If playback fails em um device, convertendo to MP3 ou AAC Geralmente solves it.
Upload the AMR to KaijuConverter e pick MP3, WAV, FLAC, AAC, OGG, ou any other target. Our FFmpeg pipeline decodes the audio e re-encodes para o target formato at sensible default bitrates (VBR ~190 kbps para music, 96 kbps para speech). Metadata e cover art travel com the audio where both formatoos support them.
AMR can be com perdas ou sem perdas depending no specific variant. com perdas variants (smaller files) discard some audio detail durante compressão in ways tuned to be inaudible; sem perdas variants preserve every sample exactly mas produce larger files. para distribution, com perdas at alta bitrate is padrão; para archival, sem perdas wins.