How do I convert M4B to AU?

Drop your M4B file onto the converter above, make sure AU is selected, and click Convert. When it's done, download the AU file — it usually takes a few seconds.

Is it safe to convert M4B to AU here?

Yes. M4B to AU conversion happens entirely inside your browser using WebAssembly, so your file is never uploaded to any server.

Is the M4B to AU converter free?

Yes — free with no watermark. Signed-out visitors can convert 25 files a day, and a free account raises that to 250.

Will converting M4B to AU reduce quality?

No — AU preserves the content of your M4B file as faithfully as the format allows.

Can I convert multiple M4B files at once?

Yes. Add up to 5 files at a time without an account, 10 with a free account and up to 500 on paid plans, then download them individually or as a single ZIP.

Can I convert AU back to M4B?

Yes — use our AU to M4B converter. Note that converting back and forth between formats can't recover detail lost to lossy compression.

AU→M4B M4B→MP3 MP3→AU M4B→WAV MP4→AU M4B→M4A WAV→AU M4B→FLAC MOV→AU M4B→AAC M4A→AU M4B→OGG M4B→Opus M4B→WMA M4B→AIFF M4B→AMR M4B→AC3 M4B→MP2 M4B→WEBA M4B→OGA M4B→MKA M4B→WV M4B→TTA WebM→AU FLAC→AU MKV→AU AAC→AU AVI→AU OGG→AU WMV→AU Opus→AU WMA→AU FLV→AU M4V→AU MPEG→AU 3GP→AU AIFF→AU AMR→AU MPG→AU TS→AU MTS→AU VOB→AU PNG→JPG JPG→PNG PNG→WebP JPG→WebP WebP→PNG WebP→JPG HEIC→PNG HEIC→JPG MP4→MP3 PNG→JPEG JPG→JPEG JPEG→PNG JPEG→JPG PNG→PDF JPG→PDF PDF→PNG PDF→JPG HEIC→WebP MP4→WebP PDF→DOCX DOCX→PDF JPEG→WebP WebP→JPEG PNG→GIF JPG→GIF GIF→PNG GIF→JPG MP4→MOV MOV→MP4 WebP→PDF HEIC→JPEG WebP→GIF GIF→WebP HEIC→PDF MP3→WAV WAV→MP3 JPEG→PDF PDF→JPEG SVG→PNG SVG→JPG HEIC→GIF MOV→MP3 MP4→GIF GIF→MP4 JPEG→GIF GIF→JPEG PNG→AVIF JPG→AVIF AVIF→PNG AVIF→JPG MP3→M4A M4A→MP3 GIF→PDF SVG→PDF PNG→SVG JPG→SVG PDF→SVG SVG→WebP MOV→WebP MP4→WAV MP4→WebM WebM→MP4 WebP→AVIF AVIF→WebP WebP→SVG SVG→JPEG MP4→MKV MKV→MP4 HEIC→AVIF MP4→M4A JPEG→AVIF AVIF→JPEG JPEG→SVG MOV→GIF GIF→MOV WebM→MP3 AVIF→PDF MP3→FLAC FLAC→MP3 MP4→AVI AVI→MP4 MKV→MP3 GIF→AVIF AVIF→GIF SVG→GIF GIF→SVG WebM→WebP MOV→WAV XLSX→PDF CSV→PDF EPUB→PDF PDF→EPUB MOV→WebM WebM→MOV MKV→WebP PNG→ICO JPG→ICO ICO→PNG ICO→JPG MP3→AAC WAV→M4A AAC→MP3 M4A→WAV MP4→FLAC AVI→MP3 MOV→MKV MKV→MOV MOV→M4A DOCX→EPUB EPUB→DOCX CSV→DOCX PDF→TXT DOC→PDF TXT→PDF WebP→ICO ICO→WebP PPTX→PDF AVI→WebP

M4BAU

Convert M4B to AU

Free, fast and private. Your M4B files are converted right in your browser — nothing is uploaded.

Runs in your browser
No watermark
Batch & ZIP download

How to convert M4B to AU

1
Add your M4B files
Drag and drop M4B files onto the converter, paste them, or click to browse. You can add several at once.
2
Choose AU
AU is already selected. Open Options if you want to change quality, size or metadata.
3
Convert
Click Convert. Your files are converted right in your browser in seconds.
4
Download your AU
Download each AU file, or everything at once as a ZIP.

M4B vs AU

From

M4B · MPEG-4 Audiobook

M4B is an MP4 audio file flagged as an audiobook, supporting chapters and resume position.

Type: Audio
Extension: .m4b
MIME: audio/mp4
Best for: audiobooks on Apple Books and other players

Lossy compression

All M4B conversions →

AU · Sun Audio

AU is a simple audio format introduced by Sun Microsystems, common on early Unix systems and Java.

Type: Audio
Extension: .au
MIME: audio/basic
Best for: legacy Unix and Java applications

Legacy format

All AU conversions →

Need it the other way around? Convert AU to M4B.

Related conversions

M4B to AU: frequently asked questions

Free, private and in your browser

Convert M4B to AU in seconds.

No sign-up, no watermarks, no waiting in line. Drop a file and get it back in the format you need.

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Most conversions never leave your device
Cloud files deleted automatically
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Convert M4B to AU

How to convert M4B to AU

Add your M4B files

Choose AU

Convert

Download your AU