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Convertto

Video Converter

Convert video between MP4, WebM and MKV entirely in your browser.

To convert a video, add your file and choose an output format. MP4 with H.264 plays almost everywhere, while WebM with VP9 produces noticeably smaller files. Conversion runs on your own device using FFmpeg compiled to WebAssembly — nothing is uploaded.

Runs in your browser
Engine
FFmpeg compiled to WebAssembly
First run
Downloads ~30 MB of FFmpeg core, then cached
Upload
None — the file never leaves your device
Privacy
Runs entirely in your browser — nothing is uploaded
Cost
Free, unlimited, no sign-up

Frequently asked questions

Which format should I choose?

MP4 with H.264 for maximum compatibility — every browser, phone and TV plays it. WebM with VP9 for the web when file size matters, typically 25–35% smaller at similar quality.

Why is the first run slow?

The FFmpeg WebAssembly core is about 30 MB and downloads once per session. After that it stays in the browser cache, and subsequent conversions start immediately.

Is my video uploaded anywhere?

No. FFmpeg runs inside your browser as WebAssembly, so the file is read from disk into memory and never sent to a server. That is also why there is no file size limit beyond your available RAM.

Why is it slower than desktop FFmpeg?

WebAssembly runs single-threaded here and cannot use your GPU, so encoding is typically several times slower than a native build. For a short clip that is fine; for a feature-length film, use desktop FFmpeg.

How to use the video converter

  1. 1Select your video file — the file stays on your device and is never uploaded.
  2. 2Choose the convert to.
  3. 3Choose the quality.
  4. 4Choose the resolution.
  5. 5Press Run, then download the result when it is ready.

Embed this tool

Put the working video converter on your own site. It runs in your visitors' browsers exactly as it does here — free, no account, nothing uploaded.

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