Someone shipped a full FFmpeg build that runs in your browser, processes files locally, and works offline.
FFmpeg WebCLI compiles FFmpeg to WebAssembly and runs it entirely inside a browser tab. Processing happens in a Web Worker, keeping the main thread responsive. After the first load, the tool installs as a Progressive Web App and runs without a network connection. Your files never touch a server.
Most browser-based video tools are thin fronts for server-side pipelines. Your footage leaves your machine, gets processed somewhere in the cloud, and comes back. Running FFmpeg client-side cuts that loop out entirely, which matters for sensitive footage, spotty connections, or anyone who has hit an upload size limit one too many times.
FFmpeg's feature set is enormous, and WASM running in a browser tab is not a supercomputer. Whether it holds up on a demanding job, 4K transcodes or complex filter chains, without grinding the tab to a halt is still the real test. That said, for the common cases, this is a more serious privacy guarantee than any cloud tool can offer.