Ffmpegwasm/ffmpeg.wasm – GitHub

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ffmpeg.wasm is a pure Webassembly/Javascript port of FFmpeg. It allows recording, converting and streaming video and audio directly within browsers.

AVI to MP4 Demo

Try it: https://ffmpegwasm.netlify.app

Check the next steps of ffmpeg.wasm HERE

Installation node Since

we are using experimental functions, you need to add flags to run in Node.js


Or, using an in-browser script tag (only works in some browsers, see list below):

SharedArrayBuffer is only available for isolated cross-origin pages. Therefore, you must host your own server with the headers Cross-Origin-Embedder-Policy: require-corp and Cross-Origin-Opener-Policy: same-origin to use ffmpeg.wasm.

Only browsers with SharedArrayBuffer support

can use ffmpeg.wasm, you can check HERE for the full list.


ffmpeg.wasm provides easy-to-use APIs, to

transcode a video you only need a few lines of code:

Use another version of ffmpeg.wasm-core /@ffmpeg/core For each version of


, there is a default version of @ffmpeg/core

(you can find it in devDependencies de package.json), but sometimes you may need to use a newer version of @ffmpeg/core to use the latest/experimental features.


Simply install the specific version you need:

Or use your own version

with custom path


Note that for webworkers and nodejs support, this will default to a local path, so you’ll try to search for ‘static/js/ffmpeg.core.js’ locally, often resulting in a local resource error. If you want to use a major version hosted on your own domain, you can refer to it relatively like this


To view the list of available versions and their changelog, verify: https://github.com/ffmpegwasm/ffmpeg.wasm-core/releases

Use single-threaded version


Multithreading must be configured by external libraries, only the following libraries now support it:


Run it in multithreading mode by default, no need to pass any arguments.


You need to pass -row-mt 1, but you can only use one thread to help, it can speed up about 30%

API Documentation

  • Supported external libraries

Frequently Asked Questions

What is the license

for ffmpeg.wasm?

There are two components inside ffmpeg.wasm:

@ffmpeg/ffmpeg (https://github.com/ffmpegwasm/ffmpeg.wasm) @ffmpeg/core (

  • https://github.com/ffmpegwasm/ffmpeg.wasm-core) @ffmpeg/core

contains WebAssembly code that is extracted from the original FFmpeg C code with minor modifications, but generally follows the same licenses as FFmpeg and its external libraries (as each external library can have its own license).

@ffmpeg/ffmpeg contains a kind of container to handle the complexity of loading the kernel and calling low-level APIs. It is a small code base and licensed under MIT.

Can I use ffmpeg.wasm in Firefox?

Yes, but only for Firefox 79+ with the proper header on both the client and server, visit https://ffmpegwasm.netlify.app to test if your Firefox works.

For more details: #106

What is the maximum input file size?

2 GB, which is a strict limit in WebAssembly. It could become 4GB in the future.

How can I build my own ffmpeg.wasm?

In fact, it’s ffmpeg.wasm-core that most people would like to build.

To build on your own, you can check build.sh within https://github.com/ffmpegwasm/ffmpeg.wasm-core repository.

You can also check out this series of posts to learn more fundamental concepts:

  • https://jeromewu.github.io/build-ffmpeg-webassembly-version-part-1-preparation/
  • https://jeromewu.github.io/build-ffmpeg-webassembly-version-part-2-compile-with-emscripten/
  • https://jeromewu.github.io/build-ffmpeg-webassembly-version-part-3-v0.1/
  • https://jeromewu.github.io/build-ffmpeg-webassembly-version-part-4-v0.2/

Why doesn’t it work in my on-premises environment?

When calling ffmpeg.load(), by default it looks for http://localhost:3000/node_modules/@ffmpeg/core/dist/ to download essential files (ffmpeg-core.js, ffmpeg-core.wasm, ffmpeg-core.worker.js). You need to make sure that you have those files served there.

If you have those files serving in another location, you can rewrite the default behavior by calling createFFmpeg():

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