Your files stay on your Mac.
AU (Audio Unix) is a simple uncompressed audio container native to Unix, NeXT, and Java sound environments. Converting FLAC to AU decodes the lossless-compressed audio and writes raw PCM samples into the AU wrapper — no quality change, just a different container. The resulting files work directly with tools and runtimes that expect the AU format.
Drag individual FLAC files or an entire folder into Convertessa. Files stay on your Mac and are never uploaded anywhere.
Choose AU from the output list. Convertessa decodes each FLAC file and rewrites the PCM audio into the AU container.
Click Convert. Convertessa processes all files locally and saves the AU files alongside the originals.
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. FLAC is lossless-compressed and AU holds uncompressed PCM, so every audio sample is preserved exactly. The conversion is a decode-and-repack, not a transcode.
AU is a simple audio container developed by Sun Microsystems. It is the native audio format for the Java Sound API and is common in Unix and NeXT environments, making it useful for Java applications and legacy Unix tools that expect AU files.
Yes. Drop an entire folder into Convertessa and all FLAC files inside are converted together. From the command line, run convertessa /path/to/folder --to au to process the whole directory in one pass.