Your files stay on your Mac.
AAC is a lossy format — audio data is permanently discarded at encode time. Converting to FLAC decodes the AAC stream and stores every remaining sample in a lossless container. The result is a bit-exact copy of the decoded audio, ready for archiving or lossless playback.
Drag one file or an entire folder onto Convertessa. The app reads every .aac file it finds — no manual file-picking required for batch jobs.
Choose FLAC from the output format list. Convertessa will decode each AAC file and encode the raw audio into a lossless FLAC container, preserving the full resolution of the decoded stream.
Click Convert. Files are processed locally on your Mac — nothing is uploaded. When the job finishes, your FLAC files are ready 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, but the original AAC encoding already discarded audio data permanently. The output is a lossless copy of the decoded AAC audio — not a restoration of the source recording.
Yes. FLAC stores every decoded sample without lossy compression, so output files are typically 3–6× larger than the source AAC files.
Yes. Drop a folder onto Convertessa and it processes every .aac file inside. From the command line, run convertessa /path/to/folder --to flac.