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AMR (Adaptive Multi-Rate) is the voice codec that powered billions of mobile phone calls during the 2G and 3G era. Developed by Ericsson and standardized by 3GPP, AMR-NB operates at 8 kHz with bitrates from 4.75 to 12.2 kbps, producing the characteristic "telephone voice" sound. Converting Opus — the state-of-the-art codec from Xiph.org that handles everything from 6 kbps narrowband to 510 kbps full-bandwidth stereo — to AMR sacrifices nearly all audio quality in exchange for compatibility with the oldest mobile telephony infrastructure.
This conversion makes sense only in specific telecommunications scenarios: feeding audio into IVR (Interactive Voice Response) systems, testing mobile network voice paths, or creating ringtones for ultra-basic feature phones. The output is tiny (under 100 KB per minute) but limited to telephone-grade 300-3400 Hz bandwidth.
AMR is the required input format for many telecom testing tools, IVR platforms, and voice quality assessment systems built for 2G/3G networks. If you have Opus recordings from modern VoIP systems and need to compare them against mobile network quality benchmarks, AMR is the standard reference format. Certain carrier-grade voice quality monitoring tools from Rohde & Schwarz, JDSU, and Spirent accept only raw AMR input.
Basic feature phones from manufacturers like Nokia, Samsung, and Itel still being sold in developing markets play AMR natively but lack codecs for Opus, MP3, or even AAC. For humanitarian organizations distributing audio content via basic phones, AMR is often the only viable format. The extremely small file sizes (under 100 KB per minute) also make AMR practical for distribution over 2G networks with severe bandwidth constraints.
FFmpeg decodes the Opus stream (48 kHz, up to 510 kbps) and re-encodes using libopencore-amrnb at 8 kHz sample rate. The AMR-NB codec operates in discrete modes with bitrates of 4.75, 5.15, 5.9, 6.7, 7.4, 7.95, 10.2, or 12.2 kbps. The default is 12.2 kbps (Mode 7), which offers the best AMR-NB quality. All audio above 3.4 kHz is discarded during the sample rate conversion from 48 kHz to 8 kHz. The output uses the simple AMR file format with a #!AMR\n header.
Extreme quality reduction. Opus can encode full-bandwidth stereo audio at up to 510 kbps with a 48 kHz sample rate. AMR-NB is limited to 300-3400 Hz mono at 12.2 kbps maximum. Music becomes unrecognizable, environmental sounds disappear, and only clear speech remains intelligible. This is purely a compatibility-driven conversion.
| Device | Opus | AMR |
|---|---|---|
| Windows PC | Partial | Partial |
| macOS | Partial | Partial |
| iPhone/iPad | Partial | Partial |
| Android | Partial | Partial |
| Linux | Partial | Partial |
| Web Browser | No |
Resolution: N/A
Bitrate: 320 kbps
OGG Vorbis preferred
Resolution: N/A
Bitrate: 256 kbps
AAC format required
Resolution: N/A
Bitrate: 128 kbps
Lossless FLAC/WAV for best quality
Resolution: N/A
Bitrate: 128 kbps
MP3 mono for spoken word
Opus to AMR is a specialized conversion for telecom professionals, IVR systems, and feature phone distribution. The quality loss is severe but intentional — AMR exists for telephony compatibility, not audio fidelity. Use it only when the target system or device specifically requires AMR format.
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| No |
| Χαρακτηριστικό | Opus | AMR |
|---|---|---|
| Πλήρες όνομα | Opus Audio Codec | Adaptive Multi-Rate Audio |
| Επέκταση | .opus | .amr |
| Ιδανικό για | Low latency | Speech optimized |