Building a Privacy-First Video Converter with WebAssembly

The Problem Every time you use a typical online video converter, your file gets uploaded to a remote server. For most people that is mildly concerning. For anyone working in healthcare, law, or finance it can be a compliance violation. HIPAA, GDPR, and internal data policies all have something to say about sending sensitive media to a third party. I wanted a converter that was truly private — one where the file never leaves the user's machine. The Solution: FFmpeg + WebAssembly FFmpeg is the gold standard for media processing. Thanks to Emscripten, it can be compiled to WebAssembly and run inside a browser tab. That means: Zero server uploads. The file stays on your device from start to finish. Full FFmpeg power. 30+ video and audio formats, codec control, bitrate tuning. Works offline once the WASM binary is cached. How It Works Under the Hood The user drops a file onto the page. A File object is created — no network request. The file bytes are written into an in-memory virtual filesy