Audio tool

Convert M4B Files to Opus on Your Device

Convert M4B to Opus in your browser for low-latency delivery. The source remains on your device throughout local processing.

Route M4B → OPUS

or drop here · up to 500 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.

Ready

Use upload name

The device processor performs decoding and encoding during the job during this M4B-to-Opus job.
High-resolution M4B footage increases conversion time and memory use.
Check picture, sound, and timing in Opus before removing the source.

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

M4B to Opus taking too long? Process a shorter section to determine whether file size is the bottleneck.
Opus converted from M4B not opening? Test a compatible player and inspect the output streams.
Inspect the generated streams when an app recognizes Opus but refuses playback.

When does M4B to Opus conversion make sense?

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

Where is the M4B source processed?

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

How can I approve Opus converted from M4B?

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

Quick use cases