Your files stay on your Mac.
AU is a raw audio container from the Unix/NeXT era, rarely supported by modern Apple software. Converting to M4A wraps your audio in AAC inside Apple's MPEG-4 container — the native format for iTunes, Apple Music, and every Apple device. Convertessa runs the entire conversion on your Mac; your files never leave the machine.
Drag one AU file or an entire folder of AU files into Convertessa. Batch conversion processes every file in one pass.
Pick Apple M4A from the output list, then set quality to match your listening or storage needs. M4A uses AAC encoding, so quality controls how much the audio is compressed.
Click Convert. Convertessa encodes each AU file to M4A locally — no upload, no server wait.
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 sent to any server.
Yes. Drop a folder onto Convertessa and it converts every AU file inside in a single batch. From the CLI: convertessa /path/to/folder --to m4a.
M4A (AAC) is lossy, so Convertessa lets you set quality before converting. Higher quality produces a larger file; lower quality saves space. The default setting works well for most music and voice recordings.