Questions, answered.

Is my video uploaded anywhere?

No. Open the network tab in your browser while compressing — the only transfers are the encoder files loading. The video stays in your tab's memory.

Which formats work?

Anything FFmpeg can decode: MP4, MOV, WebM, MKV, AVI and most phone recordings. Output is always MP4 (H.264 video, AAC audio), which plays everywhere.

What do the presets mean?

Small uses CRF 33 — the most aggressive setting that still looks fine on a phone screen. Balanced is CRF 28, the everyday default. Quality is CRF 23, close to the original and often only modestly smaller.

Why is it slow?

The encoder runs on one thread of your CPU inside the browser sandbox. A 30‑second 1080p clip takes about a minute on a laptop; longer clips scale linearly. Keep the tab in the foreground.

Why the 500 MB limit?

The whole input and output live in browser memory. Above roughly half a gigabyte, tabs start crashing on 8 GB machines.

The result is bigger than the original.

The source was already compressed harder than the preset you picked. Try Small, or accept that the file is as small as it reasonably gets.

Does it work offline?

Once the encoder has loaded, yes — until you reload the page.