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| Name | AMR | M4A |
| Full name | AMR - Adaptive Multi-Rate | M4A - Audio-only MPEG-4 |
| File extension | .amr, .3ga | .m4a |
| MIME type | audio/amr | video/mp4 |
| Developed by | 3GPP | International Organization for Standardization |
| Type of format | Audio compression format | Media container |
| Description | The Adaptive Multi-Rate (AMR or AMR-NB or GSM-AMR) audio codec is an audio compression format optimized for speech coding. AMR was adopted as the standard speech codec by 3GPP in October 1999 and is now widely used in GSM and UMTS. | MPEG-4 Part 14 or MP4 is a digital multimedia container format most commonly used to store video and audio, but can also be used to store other data such as subtitles and still images. M4A stands for MPEG 4 Audio and is a filename extension used to represent audio files. |
| Technical details | AMR speech codec consists of a multi-rate narrowband speech codec that encodes narrowband (200-3400 Hz) signals at variable bit rates ranging from 4.75 to 12.2 kbit/s with toll quality speech starting at 7.4 kbit/s. Sampling frequency 8 kHz/13-bit (160 samples for 20 ms frames), filtered to 200-3400 Hz. | Audio-only MPEG-4 files generally have a .m4a extension. This is especially true of non-protected content. M4A is often compressed using AAC encoding (lossy), but can also be in Apple Lossless format. |
| Associated programs | Audacity, FFmpeg, MPlayer, QuickTime, VLC media player | Windows Media Player, RealPlayer, MPlayer, Media Player Classic, VLC Media Player, K-Multimedia Player |
| Wiki | https://en.wikipedia.org/wiki/Adaptive_Multi-Rate_audio_codec | https://en.wikipedia.org/wiki/MPEG-4_Part_14 |