Your files stay on your Mac.
Convertessa reads the audio track embedded in each Flash (.flv) file and writes it into a Matroska audio container (.mka). Because MKA supports lossy audio, you can set quality before converting. Everything runs locally — no upload, no cloud.
Drag one .flv file or a whole folder of them onto Convertessa. Batch conversion processes every file in the folder in a single pass.
Choose Matroska (.mka) from the output format list. Set quality to tune the audio output before you convert.
Click Convert. Convertessa extracts the audio from each Flash file and writes a matching .mka alongside it. Files never leave 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.
Higher quality values preserve more audio detail at the cost of a larger file. Lower values produce smaller files with more compression. The setting applies to every file in the batch.
Yes. Drop a folder onto Convertessa or run convertessa ./folder --to mka in the terminal. Every .flv file in that directory is converted in one pass.
No. Convertessa runs entirely offline. Your files are never uploaded — the conversion happens on your Mac only.