Video Compressor

How Video Compressor works

Shrink a video with ffmpeg running in your browser: choose a CRF quality and an optional width, and download a smaller H.264 MP4. Everything happens inside this page: the tool reads your input, runs the calculation or conversion locally, and hands the result back to you. Nothing is transmitted, because there is no backend to transmit it to.

That design choice is deliberate. Most free tool sites upload your files to a server, process them there, and quietly keep a copy. Toolcin cannot do that — the site is a set of static files. If your connection dropped the moment the page finished loading, every tool would still work.

What CRF actually controls

CRF — constant rate factor — tells the encoder how much detail it may throw away. Lower is better quality and a bigger file; 18 is visually lossless, 23 is high quality, 28 is a good default for sharing, and 32 is visibly soft.

The key property is that CRF targets quality, not size: a simple scene compresses to a small file and a busy one gets the bytes it needs. That is why the same CRF can halve one video and barely touch another.

Resolution is the bigger lever

Dropping from 1920 to 1280 wide removes 55% of the pixels before any compression happens, and a phone viewing the result cannot tell. For a clip destined for chat or a social feed, scaling to 854 px wide usually saves more than any CRF change.

Aspect ratio is preserved — the encoder is told to keep the height proportional to the new width, so nothing is stretched.

Speed, heat and honesty

Encoding runs on your CPU through WebAssembly, so it takes roughly the length of the clip on a laptop and longer on a phone, which will also get warm. The tab must stay visible or the browser throttles it.

The first run downloads about 31 MB of engine; after that it is cached. If the original was already compressed — a video sent through a chat app — the output may be no smaller, and the tool reports that instead of pretending.

What is kept

The video is re-encoded to H.264 in an MP4 container, and the audio track is re-encoded to AAC at 128 kbps. That combination plays everywhere, including iOS and older Android devices, which is the real reason to convert rather than just shrink.

Good to know

• Works offline once loaded, including on flights and in locked-down networks.
• No file size limit beyond your device's own memory.
• Free to use, with no account and no usage counter.
• Results are produced locally, so they are not logged or shared with anyone.

Questions