MP3 to M4A
Converts MP3 to M4A (AAC audio in an MP4 container) in your browser, with no upload. M4A is the format Apple's ecosystem prefers — iTunes, the Music app, CarPlay and iPhone ringtones — and AAC is more efficient than MP3 at the same bitrate.
drop your MP3 here
or click to pick a file.
At a glance
| Input formats | .mp3, plus most other audio files |
|---|---|
| Output format | M4A — AAC audio in an MP4 container |
| Bitrates | 128 to 320 kbps |
| Sample rate | Preserved from the source |
| Batch | Yes — drop several files, get a zip back |
| Practical size limit | ~500 MB per file (browser memory) |
| Uploads your file | No — runs entirely in the page |
| Signup required | No |
What actually changes
MP3 and AAC are both lossy, so this is a transcode — decode, then re-encode with a different algorithm. AAC is the newer and more capable of the two: it handles high frequencies and stereo imaging more efficiently, which is why the usual rule of thumb is that AAC at 256 kbps is roughly equivalent to MP3 at 320.
That efficiency does not help you here, though, and it is important to be clear why. You are starting from an MP3 that has already had information removed. AAC's better algorithm cannot reconstruct what is missing — it can only encode what it is given, slightly more efficiently. So the result is a marginally smaller file that sounds a little worse than the MP3 you started with.
The reason to do this is therefore compatibility, not quality. If you have any access to the original uncompressed recording, encoding AAC directly from that is meaningfully better than converting the MP3.
When you'd want this
- iPhone ringtones. iOS ringtones are AAC in an .m4r container, which is an .m4a renamed. The ringtone tool handles the length limit and naming for you.
- iTunes and the Music app, where M4A is the native format and sync behaviour tends to be more predictable than with imported MP3s.
- CarPlay and older iPod hardware, which handle AAC as a first-class format.
- GarageBand and Logic, which import M4A cleanly — though for actual editing work you want AIFF or WAV rather than any lossy format.
- Reducing file size a little when a platform imposes a hard limit and you cannot re-encode from source.
Settings that matter here
Use 256 or 320 kbps. Since you are transcoding, the encoder needs headroom to avoid compounding artefacts, and the file size saving from going lower is not worth what it costs you on the second generation.
Do not be tempted by the "AAC is more efficient, so I can use a lower bitrate" logic. That is true when encoding from a lossless source; it is not true when encoding from an MP3, because the artefacts already present in the source are themselves difficult material for an encoder to represent efficiently.
Sample rate is preserved, which is what you want — resampling adds a processing step and a small amount of alteration for no benefit in a format conversion.
What you lose
A generation of quality, for the reason above. At 320 kbps it is subtle and most listeners will not notice on most material, but it is a real loss and it is not recoverable.
Tags do not survive. ID3 metadata from the MP3 is not translated into the MP4 container's tagging system, so artist, album and cover art are dropped. Re-tag afterwards in the Music app or a tool like Mp3tag if the file is going into a library.
You also lose some compatibility in the other direction, which is easy to overlook. MP3 plays on essentially everything ever made; M4A does not. Older car stereos, cheap MP3 players and some Android media apps handle it inconsistently. If the file needs to work everywhere rather than specifically on Apple hardware, staying with MP3 is the better call — and re-encoding at 320 is not a reason to convert at all.
FAQ
Is M4A better quality than MP3?
AAC is a more efficient codec, so at the same bitrate from a lossless source it sounds better. But converting an existing MP3 to M4A cannot recover what MP3 encoding already discarded, so the result is slightly worse than your source, not better.
What's the difference between M4A, MP4 and AAC?
AAC is the codec. MP4 is the container. M4A is an MP4 container holding only audio — the .m4a extension is a convention to signal that there is no video. An .m4r ringtone is the same thing again with a different extension.
Will this work for an iPhone ringtone?
It produces the right format, but iOS ringtones must be 40 seconds or shorter and use the .m4r extension. The ringtone tool handles the trimming and naming, which is easier than doing it by hand.
Do my tags and album art transfer?
No. ID3 tags from the MP3 are not translated into the MP4 container's metadata system, so you get audio and a filename. Re-tag afterwards if the file is going into a music library.
Should I convert my whole MP3 library to M4A?
Generally no. You would lose a generation of quality on every file and gain compatibility only within Apple's ecosystem, while losing it elsewhere. It is worth doing for specific files with a specific destination, not as a bulk migration.