Tools / File Converter / M4B to AU Converter

M4B to AU Converter

Convert M4B files to AU. Free, without uploading.

This tool converts M4B files to AU. Audiobook (AAC).

Sun/NeXT audio. AU is lossless, so the audio keeps the quality it has in the M4B file.

Conversion runs on your device; your file is never sent to a server. The components download once on first use, and later conversions start right away.

How to use

1. Choose the M4B file, drag it in, or paste its link.
2. Choose the audio quality; optionally enter a start and end time.
3. Press "Convert" and download the AU file.

Frequently asked questions

Will audio quality drop when converting to AU?

No. AU is lossless.

Is there a file size limit?

No fixed limit; your device’s memory decides. Computers usually handle files up to 1–2 GB.

Is my file uploaded?

No. Your M4B file is converted to AU inside your browser.