Convert Opus Files to M4B on Your Device

Convert Opus to M4B in your browser for spoken-word publishing. The source remains on your device throughout local processing.

Drop files here or browse (MAX 50 MB)

Max 50 MB per file

Preview (optional)

When your browser supports it, your audio plays here. You can still convert your file if preview does not load.

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Output file name

Conversion uses local memory and processor capacity until completion during this Opus-to-M4B job.
Available memory can limit very large Opus conversion jobs.
Review the beginning and end of M4B after the download finishes.

M4B serves audiobooks and chapter-aware Apple playback, whereas Opus commonly serves voice chat, streaming, and efficient web audio.
For Opus-to-M4B delivery, plan for chapter metadata varying by player.
After leaving Opus, the receiving app must support the streams encoded inside M4B, not only its extension.

Opus to M4B taking too long? Check available memory; long, high-resolution sources need substantially more.
M4B converted from Opus not opening? Test a compatible player and inspect the output streams.
Check whether the receiver supports this M4B variant: chapter metadata varying by player.

When does Opus to M4B conversion make sense?

It is useful when Opus media created for low-latency delivery must enter a M4B system designed for spoken-word publishing.

Where is the Opus source processed?

The browser prepares M4B from Opus on this device instead of sending the source to a remote conversion server.

How can I approve M4B converted from Opus?

Test the M4B file in the receiving app and compare duration, channels and loudness with the Opus source.

Quick use cases