M4A
Also known as: .m4a file, MPEG-4 audio, m4a vs mp3
M4A is an audio-only MPEG-4 file, the format the iPhone Voice Memos app and the iTunes/Apple Music store use. The extension is a container: most M4A files hold lossy AAC audio (small, MP3-like), but some hold lossless ALAC (large). It is the audio cousin of the MP4 video file.
- MPEG-4 container for audio only
- Usually lossy AAC; sometimes lossless ALAC
- iPhone Voice Memos and Apple Music format
M4A is a container
The `.m4a` extension marks an MPEG-4 container carrying only audio. What is inside is usually AAC — a lossy codec that delivers slightly better quality than MP3 at the same size — but it can also be ALAC, Apple’s lossless codec, which makes the file much larger.
So an AAC-based M4A is small and MP3-like, while an ALAC-based one is several times bigger. The extension alone does not tell you which; the codec inside does.
Compatibility and converting
M4A plays natively on Apple devices and most modern players. Compatibility is broad but not universal — some older players and a few apps still expect MP3.
When you need a file that works everywhere, convert M4A to MP3. The change is quick and, for an AAC source, the size stays similar.