Your files stay on your Mac.
Convertessa reads each .m4a file and writes a .aac audio stream on your Mac. If the M4A contains AAC audio — the typical case — the track passes through without re-encoding; if it holds Apple Lossless audio, Convertessa re-encodes to AAC at the quality level you choose. All processing runs locally, no upload required.
Drag one .m4a file or an entire folder into Convertessa. Batch mode processes hundreds of files in a single pass.
Choose AAC from the output format list. Because AAC is a lossy format, you can set quality to balance audio fidelity against file size before you convert.
Click Convert. Convertessa processes every file on your Mac — no internet connection required. Converted .aac files land in the destination folder you choose.
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.
If your M4A stores AAC audio (the most common case), Convertessa passes the track through without re-encoding, preserving the original quality. If the M4A stores Apple Lossless (ALAC), the audio is encoded to AAC — use the quality slider to control the output.
Yes — drop a folder onto Convertessa or run convertessa ./music/ --to aac in the terminal. Every .m4a file in the folder is converted in one pass.
Yes. Convertessa converts M4A files to AAC entirely on your Mac. No file is uploaded and no internet connection is required.