Your files stay on your Mac.
WebM is optimised for browser streaming; Matroska MKV is an open container that holds the same video and audio streams while adding support for chapters, multiple subtitle tracks, and multiple audio streams. Convertessa rewraps your WebM footage into MKV — set quality when you want to transcode the video stream, or leave the default to preserve the original encoding exactly.
Drag one file or an entire folder of WebM videos onto Convertessa. All processing runs locally — nothing is uploaded to any server.
Choose Matroska MKV from the output list. Set quality if you want to transcode the video stream; leave it at the default to rewrap the streams without re-encoding.
Click Convert. Convertessa processes every file and saves the MKV output alongside the originals, preserving the original resolution throughout.
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.
Only if the video stream is transcoded. When Convertessa rewraps the WebM streams directly into the MKV container, quality is bit-for-bit identical to the source. If you set quality, a transcode runs and the result reflects the value you choose.
Yes. Drop a folder onto Convertessa or run convertessa ./folder --to mkv from the CLI. Every WebM file inside is converted in one pass.
No. Convertessa runs entirely offline. Your video files never leave your Mac at any point during conversion.