Your files stay on your Mac.
WebM is an open, royalty-free format built for the web—every major browser plays it natively without a plugin. Convertessa reads the MKV container and re-encodes it to WebM so you can embed video directly in a web page. Everything runs on your Mac; no file is ever uploaded.
Drag one MKV file or an entire folder into Convertessa. The app lists every file it finds so you can review the queue before converting.
Pick WebM from the output format list. Set quality to control the balance between file size and visual fidelity.
Click Convert. Convertessa processes every file locally—nothing is uploaded. Finished WebM files land next to 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.
Yes. Convertessa preserves the original frame size when converting MKV to WebM—no scaling is applied.
Yes. Drop a folder onto Convertessa, or run convertessa /path/to/folder --to webm from the command line. Every MKV in the folder is converted in one pass.
Use the quality slider before you click Convert. A higher value preserves more detail at the cost of a larger file.