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For 0.11.x, visit and 0.11.x branch.


ffmpeg.wasm is a pure WebAssembly / JavaScript port of FFmpeg enabling video & audio record, convert and stream right inside browsers.

We leverage Emscripten to transpile FFmpeg source code and many libraries to WebAssembly and develop a minimal but essential library to free developers from common requirements like running ffmpeg inside web worker and more.


  • Security: your users' data only lives inside their browser, no need to worry about any data leakage or network latency.
  • Client-side computing: instead of hosting a cluster of server-end servers, you can now offload multimedia processing to client-side.
  • Flexible: ffmpeg.wasm comes with single-thread and multi-thread cores, you can use whichever fits your use case.



Multimedia transcoding is a resource-intensive task that you don't want to execute in main thread, thus in ffmpeg.wasm we offload those task to web worker (ffmpeg.worker) by default. This makes almost all function calls in ffmpeg.wasm are asynchronous and it is recommended to use async / await syntax.

ffmpeg.worker downloads WebAssembly code (ffmpeg-core) from CDN and initialized it in WorkerGlobalScope. For any input video file you would like to process, you need to first populated them inside ffmpeg-core File System and also read result from ffmpeg-core File System once it is done.

If you are using a multi-thread version of ffmpeg-core, more web workers will be spawned by ffmpeg-core inside ffmpeg.worker


The concept of core in ffmpeg.wasm is like the engine of a car, it is not only the most important part of ffmpeg.wasm but also a swappable component. Currently we maintain single-thread (@ffmpeg/core) and multi-thread version (@ffmpeg/core-mt) cores, you can build your own core (ex. a core with x264 lib only to minimize ffmpeg-core.wasm file size) using build scripts in the repository.


All ffmpeg.wasm packages are under @ffmpeg name space:

@ffmpeg/ffmpegffmpeg.wasm main package
@ffmpeg/utilcommon utility functions
@ffmpeg/typesTypeScript types
@ffmpeg/coresingle-thread ffmpeg.wasm core
@ffmpeg/core-mtmulti-thread ffmpeg.wasm core


ffmpeg.wasm is built with toolchains / libraries:

Emscripten3.1.40Emscripten is a toolchain for compiling C and C++ code into WebAssembly and JavaScript, making it possible to run applications written in these languages in web browsers.
FFmpegn5.1.4FFmpeg is a powerful multimedia framework that can decode, encode, transcode, and stream audio and video files. It's widely used for media manipulation and streaming.
x2640.164.xx264 is a popular video encoding library that provides high-quality H.264 video compression. It's commonly used for video encoding and transcoding.
x2653.4x265 is a video encoding library that specializes in encoding videos using the H.265/HEVC codec, offering high compression efficiency for video content.
libvpxv1.13.1libvpx is an open-source video codec library used for encoding and decoding VP8 and VP9 video formats, commonly used for web-based video streaming.
lame3.100LAME is an audio encoder that converts audio files to the MP3 format, making it widely used for creating MP3 audio files.
oggv1.3.4Ogg is a multimedia container format, and this library provides support for encoding and decoding audio and video in the Ogg format.
theorav1.1.1Theora is an open video codec designed for efficient video compression within the Ogg multimedia framework.
opusv1.3.1Opus is a versatile audio codec capable of handling both voice and music with low latency and high-quality compression.
vorbisv1.3.3Vorbis is an open-source audio codec known for its high audio quality and efficient compression. It's often used for audio streaming.
zlibv1.2.11zlib is a compression library that provides data compression and decompression functionality, commonly used in file compression formats like gzip.
libwebpv1.3.2libwebp is a library for working with the WebP image format, offering efficient image compression for web use
freetype2v2.10.4FreeType 2 is a library for rendering fonts. It is commonly used for text rendering in applications and systems.
fribidiv1.0.9FriBidi is a library for handling bidirectional text (text containing both left-to-right and right-to-left scripts) and is often used in text layout and rendering.
harfbuzz5.2.0HarfBuzz is a text shaping engine that allows complex script text to be rendered correctly. It's used in conjunction with font rendering libraries.
libass0.15.0libass is a library for rendering and formatting subtitles in multimedia applications, making it essential for displaying subtitles alongside video content.
zimg3.0.5zimg implements the commonly required image processing basics of scaling, colorspace conversion, and depth conversion.