FFmpeg in the Browser with WebAssembly
How ffmpeg.wasm works — running FFmpeg in the browser with WebAssembly for video processing.
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Tags: FFmpeg WebAssembly browser, ffmpeg.wasm guide, browser video processing WASM
FFmpeg in the Browser with WebAssembly FFmpeg is the most capable open-source video processing tool ever built — a 20-year-old C program that handles virtually every video and audio format. Running it in a browser without any server involvement was impossible until WebAssembly changed the equation. --- What Is FFmpeg? FFmpeg is a command-line utility for video and audio processing. It can: Decode and encode virtually every video/audio format Trim, concatenate, and merge media files Convert between containers (MP4 → WebM, MOV → MP4) Scale, rotate, and filter video Extract audio tracks Generate GIFs from video Extract thumbnails The FFmpeg project is C/C++ source code compiled to native binaries for Windows, macOS, and Linux. It runs extremely fast — typically processing video at 5–50×…
Frequently Asked Questions
What is ffmpeg.wasm?
ffmpeg.wasm is a WebAssembly port of FFmpeg — a compilation of the FFmpeg C/C++ source code to WASM bytecode that runs in a browser tab or Node.js. It exposes a JavaScript API that mirrors FFmpeg's command-line interface, allowing video and audio processing entirely client-side.
How does FFmpeg run in the browser?
The FFmpeg C source code is compiled to WebAssembly using Emscripten. WASM bytecode runs in a sandboxed environment inside the browser's JavaScript engine at near-native speed. The WASM module receives file data as typed arrays (in a virtual filesystem) and writes output back to typed arrays, which JavaScript then converts to downloadable Blobs.
What video operations can I do with ffmpeg.wasm?
ffmpeg.wasm supports most FFmpeg operations: trimming (stream copy or re-encode), format conversion (MP4 to WebM, MOV to MP4), GIF creation from video, thumbnail extraction, audio extraction, bitrate changes, resolution scaling, and frame rate adjustment. Operations requiring hardware acceleration or very large files have practical limits.
What are the limitations of browser-based FFmpeg?
Key limitations: single-threaded WASM runs at 20–40% of native speed; the WASM binary is 30–50 MB (loaded once and cached); operations on files larger than 500 MB may exhaust browser memory; hardware-accelerated encoding (NVENC, QuickSync) is not available; and multi-threaded ffmpeg.wasm requires COOP/COEP headers that can break third-party scripts.
How do I use ffmpeg.wasm in React?
Install @ffmpeg/ffmpeg and @ffmpeg/core. Load the FFmpeg instance once (typically in a useEffect or on user action), write the input file to the virtual filesystem with ffmpeg.writeFile(), run the command with ffmpeg.exec(), then read the output with ffmpeg.readFile() and create a Blob URL for download. Use the single-thread core (@ffmpeg/core) to avoid COOP/COEP header requirements.
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