M4A files: AAC in an MP4 box, and why iTunes chose it
What an M4A really is, how it differs from MP3 and AAC, and which files carry DRM. Convert M4A in your browser, no upload.
At a glance
- Type
- Audio
- Compression
- Lossy
- Container format
- Yes
- Extensions
- .m4a
- MIME type
- audio/mp4
- Common codecs
- aac, alac
An M4A is an MP4 container holding audio and nothing else — normally an AAC track. That is the whole definition. The extension exists because a file called .mp4 with no video confuses players and users alike, so Apple adopted .m4a for the audio-only case when iTunes standardised on AAC in the early 2000s.
Read more
AAC is the better codec, and by a clear margin over MP3 at the same bitrate: it was designed a decade later with the benefit of everything MP3 got wrong. That is why it became the default for iTunes, YouTube audio, broadcast, and essentially every format designed after 1999. If you are choosing where to encode from a lossless master, AAC in an M4A is a better destination than MP3 unless something specifically needs MP3.
The container matters more than people expect. A bare .aac file is a raw stream with no index and no tags, so players show no title and often cannot seek within it. Wrapping the same audio in M4A fixes both, which is why M4A rather than .aac is what you should almost always choose when extracting audio here.
Two caveats. Files bought from the iTunes Store may carry FairPlay DRM, and nothing that respects the encryption can read them — those conversions fail rather than complete. And extracting to M4A here re-encodes rather than copying the original AAC track, so it is a second lossy generation just like MP3; choose WAV if the point is to avoid re-compression.
Convert M4A to other formats
Convert other formats to M4A
FAQ
Is M4A the same as AAC?
Nearly. AAC is the codec; M4A is the MP4 container that holds it, along with tags and an index. A bare .aac file has the same audio but no container, which is why players handle it worse.
Is M4A better than MP3?
At the same bitrate, yes — AAC holds more detail. MP3's advantage is compatibility with hardware that predates AAC, which is the only reason to convert in that direction.
Why will my M4A not convert?
Almost certainly FairPlay DRM, which iTunes Store purchases carry. Encrypted files cannot be read by anything that respects the encryption. Voice memos and files you made yourself convert normally.
Does extracting to M4A copy the original AAC track?
No, it re-encodes, which is a second lossy pass. There is no setting here that lifts the original track out unchanged — extract to WAV if you need to avoid re-compression.
Will M4A play on Android and Windows?
Yes. Support is effectively universal now; the format's association with Apple is historical rather than technical.
What are iPhone voice memos saved as?
M4A. That is why converting M4A to WAV is a common step before transcription or noise reduction, since those tools generally want uncompressed PCM.
M4A or M4B — what is the difference?
M4B is the same container marked as an audiobook, so players remember your position. Unprotected M4B files convert here the same way; DRM-protected ones do not.
What bitrate should I use?
192 kbps is a good default, and because AAC is more efficient it sounds better than an MP3 at the same rate. There is no benefit in exceeding the bitrate of the source track.