AAC audio in an MP4 container — the format of iTunes and Apple Music, which plays almost everywhere.

Can I convert M4B to M4A and keep the chapters?

Yes. The sound is copied as is and the chapters are kept.

Why can't Firefox convert everything to M4A?

Firefox has no AAC encoder yet; it can only copy sound that's already AAC.

Audio to M4A Converter

Convert MP3, WAV, FLAC, MP4 and other audio files — or the sound of a video — to M4A in your browser — nothing is uploaded.

MP3, WAV, FLAC, M4A, M4B, MP4, AAC, OGA or WEBA, one or many. Drop them here or paste with ⌘V / Ctrl+V. Choose what each becomes on its row.

Runs on your device. Files are read and converted in your browser and aren't uploaded.

M4A

Lossy
Apple's format
Keeps chapters

AAC audio in an MP4 container — the format of iTunes and Apple Music purchases, iPhone voice memos and many recorders. It sounds a little better than an MP3 of the same size, and plays on Apple devices, Android, Windows and in browsers.

M4A Converter — convert M4A files to any format

Learn more about converting audio to M4A

When you'd do this

You want everything as M4A — for Apple devices and apps, for small files that sound good, or to turn an audiobook M4B into a plain M4A without losing its chapters.

What to expect

Encoded, a minute of M4A is about 0.9 MB at 128 kbps, about 1.4 MB at 192 kbps or about 1.8 MB at 256 kbps. From an MP4, M4B or AAC file the sound is usually copied instead, so the M4A is about the size of the sound it came from.

Recommended settings

192 kbps (the default) for music; 128 kbps for speech. A copied file keeps its own bitrate.

Where it plays

Apple devices and apps first of all — Music, iTunes and QuickTime — and Android, Windows and every modern browser too.

Good to know

From MP4, M4B and AAC files, AAC sound is copied as is — no re-encoding, no loss, and it works in Firefox too.
Firefox can't encode AAC, so there anything that isn't already AAC can't become an M4A; use Chrome, Edge or Safari.
Chapters from an M4B or M4A are kept.
An M4A made here can be up to 5 hours long (12 hours when the sound is copied).

How to do it

Choose your audio files, or drop them on the page — any mix of formats.
Each is set to M4A. Change one on its own row if you like, and the AAC bitrate and the channels in Settings.
Convert all, then download each M4A, or all of them in one .zip.

Questions

What is an M4A file?: AAC audio in an MP4 container — the format of iTunes and Apple Music, which plays almost everywhere.
Can I convert M4B to M4A and keep the chapters?: Yes. The sound is copied as is and the chapters are kept.
Why can't Firefox convert everything to M4A?: Firefox has no AAC encoder yet; it can only copy sound that's already AAC.