About
A video compressor that does not upload your file
Video Size Reducer is a free single-purpose tool for making an MP4 smaller. It exists because most online compressors require uploading your video to someone else's server first.
How the compression works
The tool reads your selected video through standard browser media APIs and re-encodes it on your own device. It uses the browser's built-in WebCodecs support where available, and falls back to a WebAssembly build of ffmpeg for formats the browser cannot handle natively. Both run inside the page — there is no application server that receives your video.
Because encoding happens locally, speed depends on your device rather than on a queue. A large file on an older laptop will take longer than the same file on a recent machine, and the browser tab needs to stay open while it works.
What it is good at, and what it is not
It is built for the common case: an MP4 that is too large to send or upload, which needs to hit a target size or a lower quality preset. It is not a video editor. There is no trimming, no filters, no format conversion matrix, and no batch queue.
Cost and accounts
The tool is free and does not ask for an account. Site running costs are covered by the operator; see the privacy policy for what usage data the site collects.
Who maintains it
Video Size Reducer is built and maintained by an independent developer. Bug reports and feature requests are welcome through the contact page.