Your files stay on your Mac.
AU is a legacy raw audio container developed by Sun Microsystems. Converting to Opus re-encodes that audio using the Opus codec—a modern lossy format that achieves high fidelity at low file sizes. Set the quality level to balance file size against listening quality.
Drag one AU file or an entire folder of AU files onto Convertessa. Files stay on your Mac throughout.
Pick Opus from the output format list. Set the quality level to control the trade-off between file size and audio fidelity.
Click Convert. Convertessa re-encodes each AU file to Opus locally, preserving the original resolution of the audio stream.
Images, audio, video, documents, archives and eBooks — all converted natively, right on your Mac.
Pick a format you have — see everything Convertessa can turn it into.
Convert hundreds of files at once with per-type group defaults and individual overrides.
First-class support for HEIC, AVIF and WebP — encode and decode, both ways. Read JPEG XL and a dozen more modern formats too.
Drop files anywhere on the window. Native, instant, and exactly what you’d expect on a Mac.
Dial in compression, resolution and bitrate. Keep originals pristine or shrink for sharing.
Never overwrite a file by accident. Convertessa appends safe suffixes automatically.
Every job is logged locally. Re-run a previous conversion or revisit recent outputs in a click.
Bundle your converted files straight into a single ZIP, TAR or 7z — packaged and ready to share the moment a job finishes.
Right-click any file in Finder and choose Convert. A Quick Action handles it on the spot — no need to open the app first.
Shrink Convertessa to a tidy mini window that tucks into a corner — just a drop zone and a format picker for quick, one-off conversions.
No cloud. No account. No upload. Every conversion happens entirely on-device, using the power already in your Mac. What you convert is nobody’s business but yours.
Script conversions, wire them into your build, or batch a folder from the terminal. The same engine, no GUI required.
Read the full CLI documentation →Shrink Convertessa down to a small, focused window — drop, convert, done, with your recent conversions one click away.
macOS 14+ · Apple Silicon & Intel
New formats, new features, and fixes — every release, on the record.
No. Convertessa runs entirely on your Mac. AU files are read and written locally—nothing is uploaded or transmitted to any server.
Yes. Drop a folder onto Convertessa or use the CLI: convertessa /path/to/folder --to opus. Every AU file in the folder is converted in one pass.
Opus is a lossy format, so a higher quality setting preserves more of the original AU audio at the cost of a larger file. Lower settings reduce file size with some loss in fidelity.