Your files stay on your Mac.
WebM is the open web-video container used by browsers and streaming platforms; AVI is the legacy Windows container that older editors, media servers, and hardware players expect. Convertessa re-encodes your WebM files into AVI directly on your Mac — no upload, no cloud account, no internet connection required.
Drag a single .webm file or an entire folder onto Convertessa. The app lists every video it finds so you can review the queue before starting.
Choose AVI from the output format list. Set quality to balance file size against fidelity — the quality slider appears because AVI uses lossy encoding.
Click Convert. Convertessa processes every file locally and saves the AVI files alongside the originals. Nothing leaves your Mac.
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.
AVI uses lossy encoding, so some generation loss is unavoidable. Convertessa lets you set the quality level before converting, giving you direct control over the fidelity-versus-file-size trade-off. Original resolution is always preserved.
Yes. Drop a folder onto Convertessa and it queues every .webm file inside. All files are converted in one pass — no need to add them one by one.
No. Convertessa runs entirely offline. Your WebM files are read and written on your Mac — they never leave your computer.