Convert MPEG-4 Part 14 (.mp4) to Adaptive Multi-Rate Audio (.amr) online for free. Fast, secure video conversion with no watermarks or registration.
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MP4 to AMR conversion extracts the audio track from an MPEG-4 video and encodes it in Adaptive Multi-Rate format. AMR was developed by the European Telecommunications Standards Institute (ETSI) specifically for cellular voice calls over GSM and 3G networks. It operates at extremely low bitrates (4.75 to 12.2 kbps) and is optimized for human speech rather than music or general audio.
Our converter decodes the MP4 audio and re-encodes it using the AMR-NB (Narrowband) codec at 8 kHz mono. The resulting file is tiny — a 10-minute recording produces an AMR file under 1 MB.
AMR conversion makes sense when you need to extract voice content from video for telephony applications, voice messaging systems, or legacy mobile platforms. Many older VoIP systems, IVR (Interactive Voice Response) systems, and cellular voicemail platforms use AMR as their native format. If you are building content for distribution on 2G/3G networks where bandwidth is precious, AMR's extreme compression is unmatched. The format excels at speech intelligibility even at its lowest 4.75 kbps rate.
FFmpeg decodes the MP4 audio stream and re-encodes using the libopencore-amrnb encoder. The output is 8 kHz mono (narrowband), which is the AMR-NB standard. Bitrate options range from 4.75 to 12.2 kbps, with 12.2 kbps (Mode 7) providing the best speech quality. The AMR container stores frames of 20 ms each. For wideband speech, AMR-WB (16 kHz, up to 23.85 kbps) can be selected using the libopencore-amrwb encoder.
AMR is strictly a speech codec — music, environmental sounds, and complex audio will sound distorted and metallic. At 12.2 kbps, speech is clear and intelligible but noticeably compressed. At 4.75 kbps, speech remains understandable but sounds robotic. The 8 kHz sample rate means all frequencies above 4 kHz are discarded, eliminating most of what gives audio its richness. This is functional audio, not high-fidelity audio.
| Device | MP4 | AMR |
|---|---|---|
| Windows PC | Native | Partial |
| macOS | Native | Partial |
| iPhone/iPad | Native | Partial |
| Android | Native | Partial |
| Linux | Partial | Partial |
| Web Browser | Native |
Resolution: 1920x1080
Bitrate: 8-12 Mbps
H.264 recommended for fast processing
Resolution: 1080x1080
Bitrate: 3.5 Mbps
Square or 9:16 for Reels
Resolution: 1080x1920
Bitrate: 4 Mbps
9:16 vertical, under 60s ideal
Resolution: 1280x720
Bitrate: 5 Mbps
Under 140s, 512MB max
Resolution: 960x540
Bitrate: 2 Mbps
16MB limit for standard, 64MB for document
Resolution: 1280x720
Bitrate: 4 Mbps
MP4 to AMR is a specialized conversion for telephony, voice messaging, and ultra-low-bandwidth scenarios. The resulting files are remarkably small and perfectly suited for voice content delivery on constrained networks and legacy systems.
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| Funktion | MP4 | AMR |
|---|---|---|
| Fulde navn | MPEG-4 Part 14 | Adaptive Multi-Rate Audio |
| Filendelse | .mp4 | .amr |
| Bedst til | Universal compatibility | Speech optimized |