Load Multi-Threaded ffmpeg.wasm and Configure COOP/COEP

This article provides a step-by-step guide on how to load and run the multi-threaded version of ffmpeg.wasm in your web applications. You will learn how to set up the necessary Cross-Origin Opener Policy (COOP) and Cross-Origin Embedder Policy (COEP) headers on your server to enable SharedArrayBuffer support, followed by the JavaScript code required to initialize the multi-threaded FFmpeg core.

Why COOP and COEP Headers are Required

Multi-threaded ffmpeg.wasm relies on Web Workers and SharedArrayBuffer to share memory across multiple threads. Due to security vulnerabilities like Spectre, modern web browsers restrict the use of SharedArrayBuffer by default.

To enable this feature, your server must serve the HTML page with specific HTTP response headers that place the document in a secure, isolated context.

The Required Headers

You must configure your web server to send the following two HTTP headers:

Cross-Origin-Opener-Policy: same-origin
Cross-Origin-Embedder-Policy: require-corp

Server Configuration Examples

Node.js (Express)

If you are using Express, you can set these headers using middleware:

const express = require('express');
const app = express();

app.use((req, res, next) => {
  res.setHeader('Cross-Origin-Opener-Policy', 'same-origin');
  res.setHeader('Cross-Origin-Embedder-Policy', 'require-corp');
  next();
});

app.use(express.static('public'));
app.listen(3000);

Nginx

For an Nginx server, add these directives to your configuration block:

server {
    listen 80;
    server_name localhost;

    location / {
        add_header Cross-Origin-Opener-Policy "same-origin";
        add_header Cross-Origin-Embedder-Policy "require-corp";
        root /usr/share/nginx/html;
        index index.html;
    }
}

Next.js (next.config.js)

If you are using Next.js, configure the headers in your configuration file:

module.exports = {
  async headers() {
    return [
      {
        source: '/(.*)',
        headers: [
          {
            key: 'Cross-Origin-Opener-Policy',
            value: 'same-origin',
          },
          {
            key: 'Cross-Origin-Embedder-Policy',
            value: 'require-corp',
          },
        ],
      },
    ];
  },
};

Loading Multi-Threaded ffmpeg.wasm

Once the headers are configured, you can load the multi-threaded version of ffmpeg.wasm in your frontend application. You must use the multi-threaded version of the core library (@ffmpeg/core-mt) and explicitly define the worker URL during initialization.

Step 1: Install Dependencies

Install the latest versions of @ffmpeg/ffmpeg and @ffmpeg/util:

npm install @ffmpeg/ffmpeg @ffmpeg/util

Step 2: Initialize and Load FFmpeg

Import the required modules and load the multi-threaded core assets. Using a CDN like unpkg is standard, but you can also host these files locally on your server.

import { FFmpeg } from '@ffmpeg/ffmpeg';
import { toBlobURL } from '@ffmpeg/util';

const ffmpeg = new FFmpeg();

async function loadMultiThreadedFFmpeg() {
  // Use the multi-threaded (core-mt) version of ffmpeg.wasm
  const baseURL = 'https://unpkg.com/@ffmpeg/core-mt@0.12.6/dist/esm';

  try {
    await ffmpeg.load({
      coreURL: await toBlobURL(`${baseURL}/ffmpeg-core.js`, 'text/javascript'),
      wasmURL: await toBlobURL(`${baseURL}/ffmpeg-core.wasm`, 'application/wasm'),
      // workerURL is required for multi-threading
      workerURL: await toBlobURL(`${baseURL}/ffmpeg-core.worker.js`, 'text/javascript'),
    });
    console.log('Multi-threaded ffmpeg.wasm loaded successfully!');
  } catch (error) {
    console.error('Failed to load multi-threaded ffmpeg.wasm:', error);
  }
}

loadMultiThreadedFFmpeg();

Verifying the Setup

To confirm that multi-threading is working: 1. Open your browser’s Developer Tools (F12). 2. Go to the Network tab, reload the page, and select your main HTML document. Check the Response Headers to ensure Cross-Origin-Opener-Policy: same-origin and Cross-Origin-Embedder-Policy: require-corp are present. 3. Check the Console to ensure no SharedArrayBuffer or CORS-related errors are thrown during ffmpeg.load().