How It Works

Your browser does the work

Traditional online compressors upload your file to a server, compress it there and send it back. That means waiting for two transfers and trusting a company with your files.

VideosCompressor works differently. When you choose a file, the page loads a compression engine into your browser, and your own device's processor and graphics chip do the work. The file never leaves your device. The only thing that moves is the finished file, from your browser's memory to your Downloads folder.

The video engine

For most videos, the compressor uses WebCodecs, a modern browser feature that gives web pages access to the same hardware video encoders your operating system uses. It's fast and energy-efficient, and the output is a standard H.264 MP4.

For formats WebCodecs can't read, such as AVI, WMV or FLV, or on browsers without WebCodecs, the compressor switches automatically to a compatibility engine built on FFmpeg, the widely used open-source video toolkit, compiled to run in the browser. It's slower but supports far more formats. It's downloaded only the first time a file needs it.

The compressor works out the right settings from your video's length, resolution and the mode you chose. For a target size, it calculates the bitrate from the duration, and it retries automatically if a result would be even slightly too large.

The image engine

Images are decoded by your browser and re-encoded with well-known open-source encoders, compiled to WebAssembly: MozJPEG for JPG, OxiPNG for lossless PNG, libwebp for WebP and libavif for AVIF. Resizing uses a high-quality Lanczos filter. For a target size in KB, the compressor searches for the highest quality that fits.

The PDF engine

PDFs are opened with pdf-lib. The compressor recompresses and downsamples the images inside the document, compresses data stored without compression, removes leftovers such as thumbnails, and saves the structure compactly. Text, fonts and links aren't touched. The optional Maximum compression level uses PDF.js, Mozilla's PDF renderer, to turn pages into images.

What this means for your privacy

• No uploads: your files are never sent to our servers.
• No storage: we never receive your files, so we can't keep them.
• No account: we don't know who you are.
• Metadata removed by default: location and device details are stripped from compressed files unless you choose to keep them.

The website itself is a set of static files served by our hosting provider, like any other website. It uses a small number of ads to stay free; see our Privacy Policy and Cookie Policy for what advertising involves.

Limits of in-browser compression

Working on your device has a few trade-offs:

• Memory: very large files, typically over 1–2 GB on computers or 500 MB on phones, can exceed what a browser tab is allowed to use.
• Speed: compression speed depends on your device. Recent computers with hardware video encoders are fastest; older phones are slower.
• Keep the tab open: browsers pause background tabs, especially on phones, so keep the page in front until it's done.

Open source

The compressors are built on open-source software. You'll find every component, its license and a link to its source code on our Licenses page.