Your files stay on your Mac.
WebM is a container that bundles video with an audio track encoded in Opus or Vorbis. Converting to Opus drops the video stream and gives you a standalone .opus audio file. Convertessa reads the WebM container, re-encodes the audio to Opus, and saves everything locally — your files never leave your Mac.
Drag one WebM file or an entire folder onto Convertessa. Batch mode picks up every .webm file in the folder and queues them in one pass.
Pick Opus from the output list. Because Opus is a lossy format you can also set quality to balance file size against audio fidelity before you convert.
Click Convert. Convertessa re-encodes the audio track, discards the video payload, and writes your .opus files alongside the originals — no upload, no waiting.
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.
Yes. Opus is an audio-only format. The video stream is discarded and you get a standalone .opus audio file containing only the audio track.
Yes. Drag a folder onto Convertessa or run convertessa /folder --to opus in the terminal to batch-convert every .webm file in one command.
No. Convertessa runs entirely on your Mac. Files are processed locally and are never sent to any server.