node-libav-webcodecs

WebCodecs API polyfill for Node.js using libav.

Installation

``bash
npm install node-libav-webcodecs
`

Usage

Important: Use vite-node to run scripts due to node-web-audio-api compatibility issues.

`bash
npx vite-node your-script.ts
`

$3

`typescript
import { init } from 'node-libav-webcodecs/polyfill';
import * as fs from 'fs';

async function main() {
await init();

const core = await import('@diffusionstudio/core');

// Load video file
const videoBuffer = fs.readFileSync('input.webm');
const videoBlob = new Blob([videoBuffer], { type: 'video/webm' });
const source = await core.Source.from(videoBlob, { mimeType: 'video/webm' });

// Create composition
const composition = new core.Composition({
width: 1280,
height: 720,
background: '#000000',
});

// Video layer - sequential mode (clips play one after another)
const videoLayer = new core.Layer({ mode: 'SEQUENTIAL' });
await composition.add(videoLayer);

// Add video 3 times, each trimmed to 1 second
for (let i = 0; i < 3; i++) {
const clip = new core.VideoClip(source, {
position: 'center',
height: '100%',
});
clip.range = [0, 1]; // Trim to first 1 second
await videoLayer.add(clip);
}

// Rectangle overlay
const overlayLayer = new core.Layer();
await composition.add(overlayLayer);
await overlayLayer.add(new core.RectangleClip({
position: 'center',
width: 600, height: 80,
fill: '#e94560',
duration: 3,
}));

// Encode to MP4
const encoder = new core.Encoder(composition, {
video: { fps: 30, bitrate: 2_000_000 },
audio: { enabled: false },
});

const result = await encoder.render();
if (result.type === 'success') {
fs.writeFileSync('output.mp4', Buffer.from(await result.data!.arrayBuffer()));
}

process.exit(0);
}

main().catch(console.error);
`

Supported Codecs

| Type | Codecs |
|-------|--------------------|
| Video | VP8, VP9, H.264 |
| Audio | FLAC, Opus, Vorbis |

Limitations

- Audio not working - use audio: { enabled: false }
- Text requires font setup - use core.loadFont() or use shapes instead
- Use vite-node to run scripts
- Call process.exit() after completion
- Use video-only files (no audio track)

What's included

The /polyfill` entry point sets up:

| Category | APIs |
|-----------|---------------------------------------------------------------------------------------------------------------------|
| WebCodecs | VideoEncoder, VideoDecoder, AudioEncoder, AudioDecoder, VideoFrame, AudioData, EncodedVideoChunk, EncodedAudioChunk |
| Canvas | HTMLCanvasElement, OffscreenCanvas, CanvasRenderingContext2D, Image, Path2D, DOMMatrix, DOMRect |
| DOM | document, window |
| Audio | AudioContext, OfflineAudioContext, AudioBuffer, AudioWorkletNode |
| Misc | requestAnimationFrame, performance, ResizeObserver, File, HTMLVideoElement |

License

0BSD