Your files stay on your Mac.
MP4 to AU pulls the audio track out of your video file and writes it as an AU (Sun/NeXT audio) file. Conversion runs entirely on your Mac—nothing is uploaded or sent to a server. Drop a whole folder to process multiple MP4s in one pass.
Drag one MP4 or an entire folder into Convertessa. No account, no upload—every file stays on your Mac.
Pick AU from the output format list. Convertessa will extract the audio track and write it as an AU stream.
Click Convert. Convertessa processes each file locally and saves the AU output alongside your 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.
AU (also written .au or Sun audio) is a simple audio container developed by Sun Microsystems. It stores uncompressed PCM audio and is natively recognised on Unix-based systems and by many audio tools and DAWs.
AU is an uncompressed format. Convertessa writes the audio data from your MP4 at its original sample rate and bit depth without adding another lossy encoding pass, so nothing is thrown away.
Yes. Drag a folder into Convertessa or run convertessa ./videos/ --to au in your terminal. Every MP4 in the folder is converted in one pass—no uploads, no cloud processing.