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Convertto

Video Compressor

Shrink video file size with adjustable quality — locally, with no upload limit.

To compress a video, add the file and raise the quality number to make the file smaller. CRF 23 is visually lossless, 28 is a good balance for the web, and above 32 compression artefacts become visible. Downscaling the resolution saves considerably more than CRF alone.

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

What does CRF actually control?

Constant Rate Factor targets a consistent perceptual quality rather than a fixed bitrate. Every increase of about 6 roughly halves the file size. 18 is near-lossless, 23 is the x264 default, and 28 is a common web setting.

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 compressor

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

Embed this tool

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

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