MP3 to M4A Converter

M4A is AAC audio in an MP4 container: the format of iTunes, Apple Music, iPhone ringtones and many video editors. Converting MP3 to M4A makes a file that Apple apps treat as native, with the title, artist, album and cover art carried over. The conversion runs in your browser with the ffmpeg engine; nothing is uploaded.

How to use this tool

1. Choose one or more MP3 files.
2. Pick the AAC bitrate: 192 kbps keeps music sounding like the MP3, 96 kbps is enough for speech.
3. Keep tags and clipping protection on.
4. Press Calculate and download the M4A files.

Formula

M4A size ≈ AAC bitrate (kbps) × 1000 ÷ 8 × length (s)

The MP3 is decoded and encoded again as AAC-LC by the ffmpeg engine (about 30 MB, downloaded once and cached), with -movflags +faststart so the file starts playing before it is fully loaded. Tags and the cover picture are copied into the MP4 metadata. Re-encoding can push loud peaks a little over full scale, so the result is decoded again and, only if needed, lowered just enough (at most twice).

Example

A 4-minute MP3 at 320 kbps is about 9.6 MB. As M4A at 192 kbps it becomes 192,000 ÷ 8 × 240 = 5.76 MB, and AAC at that rate sounds as good as or better than MP3 at the same rate.