Your files stay on your Mac.
AU is the Unix/Sun audio container used by Java runtimes and legacy Unix toolchains. Convertessa rewraps each MP3 into an uncompressed AU file, writing PCM audio data that the target platform can read directly. Everything runs on your Mac — no files uploaded, no internet required.
Drag one MP3 or an entire folder into Convertessa. The queue accepts any number of files at once.
Select AU from the output format list. Convertessa writes a new .au file for each source MP3 and leaves your originals untouched.
Click Convert. All processing runs locally on your Mac — no upload, no internet connection needed.
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.
Convertessa writes AU files with uncompressed PCM audio. The output is lossless at the container level, though the source MP3 is already lossy — no detail discarded during MP3 encoding is recovered in the AU file.
Yes. Drag a folder into the app or run convertessa /path/to/folder --to au in the terminal. Convertessa processes every MP3 in the folder and writes a matching .au file for each one.
No. Convertessa runs entirely offline. Your MP3 files are read and written locally — nothing is uploaded to any server.