AAC vs MP3
| Property | AAC | MP3 |
|---|---|---|
| Full name | Advanced Audio Coding (raw ADTS stream) | MPEG-1 Audio Layer III |
| File extensions | .aac | .mp3 |
| Created by | MPEG (Fraunhofer, Dolby, Sony, AT&T and others) | Fraunhofer IIS and MPEG |
| Introduced | 1997 | 1993 |
| Compression | Lossy; better than MP3 at the same bitrate | Lossy |
| Codecs inside | AAC in a bare ADTS stream (no MP4 wrapper) | MP3, usually 128–320 kbps |
| Typical size | — | About 1 MB per minute at 128 kbps, 2.4 MB at 320 kbps |
| Opens on | Most phones and media players; many editors, DJ apps and upload forms expect MP3 | Every phone, computer, car stereo, speaker and app |
| Best for | Radio streams and phone recordings | Music and podcasts that must play anywhere |
Why convert AAC to MP3?
A .aac file is AAC audio without the MP4 wrapper that M4A files have: a bare stream of frames (called ADTS). Internet radio captures, some call and dictation recorders, older Android voice recorders and a few messaging apps save audio this way. Without the wrapper there is no duration or seek index, so some players show the wrong length or cannot skip, and many editors and DJ tools refuse the file.
MP3 fixes the compatibility problem. Since both are lossy, set a bitrate at or slightly above the source to avoid audible loss; for recordings of speech, 96–128 kbps mono is plenty. Alternatively, choose M4A in the full Audio Converter: it puts the same AAC audio into a proper MP4 container with no re-encoding at all.
If you have M4A files rather than .aac, see M4A to MP3; the result is the same kind of MP3.