Convert M4B files to OPUS online, free and without signup. Upload your M4B file below and download the converted OPUS in seconds. You get 10 free conversions every day, and files are automatically deleted after 24 hours.
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M4B is Apple's audiobook format supporting bookmarks.
Opus is a modern codec designed for internet streaming.
Upload your M4B file using the button above. Files up to your plan limit are supported.
Click Convert. Your file is processed on our servers with industry-standard engines like FFmpeg and LibreOffice.
Download your OPUS file. It stays available for 24 hours, then it is deleted automatically.
Yes. ConvertFly offers 10 free conversions every day with no signup required. For higher volumes, credit packages start at $8.
Yes. Files are encrypted during transfer and automatically deleted after 24 hours. ConvertFly is operated by Dizzus GmbH in Switzerland.
No. The conversion runs entirely in the cloud: it works from any browser, on desktop or mobile.
| M4B | OPUS | |
|---|---|---|
| Type | audio | audio |
| In short | M4B is Apple's audiobook format supporting bookmarks. | Opus is a modern codec designed for internet streaming. |
Convert M4B to OPUS online for free. Fast, secure audio conversion powered by industry-standard engines. No signup required, files auto-delete after 24 hours. Operated by Dizzus GmbH on private infrastructure.