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Web-Demuxer

Demux media files in the browser using WebAssembly, designed for WebCodecs.

Overview

WebCodecs provides decoding capabilities but lacks demuxing functionality. While mp4box.js is excellent for MP4 files, it only supports MP4 format. Web-Demuxer aims to support a wide range of multimedia formats in one package, specifically designed for seamless WebCodecs integration.

Features

- 🪄 WebCodecs-First Design - API optimized for WebCodecs development with intuitive methods
- 📦 Multi-Format Support - Handle mov/mp4/mkv/webm/flv/m4v/wmv/avi/ts and more formats
- 🧩 Customizable Build - Configure and build demuxers for specific formats only
- 🔧 Rich Media Info - Extract detailed metadata similar to ffprobe output

Quick Start

``bash
npm install web-demuxer
`

`typescript
import { WebDemuxer } from "web-demuxer";

const demuxer = new WebDemuxer();

// Example: Get video frame at specific time
async function seek(file, time) {
// 1. Load video file
await demuxer.load(file);

// 2. Demux video file and generate VideoDecoderConfig and EncodedVideoChunk required by WebCodecs
const videoDecoderConfig = await demuxer.getDecoderConfig('video');
const videoEncodedChunk = await demuxer.seek('video', time);

// 3. Decode video frame through WebCodecs
const decoder = new VideoDecoder({
output: (frame) => {
// Render frame, e.g., using canvas drawImage
frame.close();
},
error: (e) => {
console.error('video decoder error:', e);
}
});

decoder.configure(videoDecoderConfig);
decoder.decode(videoEncodedChunk);
decoder.flush();
}
`

Installation

$3

‼️ Important: Place the WASM file in your static directory (e.g., public/) for proper loading.

`typescript
const demuxer = new WebDemuxer({
// Option 1: Use CDN
wasmFilePath: "https://cdn.jsdelivr.net/npm/web-demuxer@latest/dist/wasm-files/web-demuxer.wasm",

// Option 2: Use local file
// Copy dist/wasm-files/web-demuxer.wasm from npm package to public directory
// You can use plugins like vite-plugin-static-copy to sync automatically
// If JS and WASM are in the same public directory, wasmFilePath can be omitted
// wasmFilePath: "/path/to/your/public/web-demuxer.wasm"
});
`

Live Examples

#### new WebDemuxer(options?: WebDemuxerOptions)

Creates a new WebDemuxer instance.

Parameters:
- options.wasmFilePath (optional): Custom WASM file path. Defaults to looking for web-demuxer.wasm in the script directory.

$3

#### load(source: File | string): Promise

Loads a media file and initializes the WASM worker.

Parameters:
- source: File object or URL string

Note: All subsequent methods require successful load() execution.

#### getDecoderConfig(type: MediaType): Promise

Gets WebCodecs decoder configuration.

Parameters:
- type: 'video' or 'audio'

Returns: VideoDecoderConfig or AudioDecoderConfig

#### seek(type: MediaType, time: number, seekFlag?: AVSeekFlag): Promise

Seeks to specific time and returns encoded chunk.

Parameters:
- type: 'video' or 'audio'
- time: Time in seconds
- seekFlag: Seek direction (default: backward)

Returns: EncodedVideoChunk or EncodedAudioChunk

#### read(type: MediaType, start?: number, end?: number, seekFlag?: AVSeekFlag): ReadableStream

Creates a stream of encoded chunks.

Parameters:
- type: 'video' or 'audio'
- start: Start time in seconds (default: 0)
- end: End time in seconds (default: end of file)
- seekFlag: Seek direction (default: backward)

Returns: ReadableStream of encoded chunks

$3

#### getMediaInfo(): Promise

Extracts comprehensive media metadata (similar to ffprobe output).

Returns:

#### getMediaStream(type: MediaType, streamIndex?: number): Promise

Gets information about a specific media stream.

Parameters:
- type: 'video', 'audio' or 'subtitle'
- streamIndex: Stream index (optional)

$3

#### seekMediaPacket(type: MediaType, time: number, seekFlag?: AVSeekFlag): Promise

Gets raw media packet at specific time.

Parameters:
- type: Media type ('video', 'audio' or 'subtitle')
- time: Time in seconds
- seekFlag: Seek direction (default: backward seek)

#### readMediaPacket(type: MediaType, start?: number, end?: number, seekFlag?: AVSeekFlag): ReadableStream

Returns a ReadableStream for streaming raw media packet data.

Parameters:
- type: Media type ('video', 'audio' or 'subtitle')
- start: Start time in seconds (default: 0)
- end: End time in seconds (default: 0, read till end)
- seekFlag: Seek direction (default: backward seek)

$3

#### setLogLevel(level: AVLogLevel): void

Sets logging verbosity level for debugging purposes.

Parameters:
- level: Log level (see AVLogLevel for available options)

#### destroy(): void

Cleans up resources and terminates worker.

Custom Demuxer

Web-Demuxer provides two pre-built versions:

| Version | Size (gzipped) | Supported Formats |
|---------|----------------|-------------------|
| Full (web-demuxer.wasm) | 1131 kB | mov, mp4, avi, flv, mkv, webm, mpeg, asf, mpegts, etc. |
| Mini (web-demuxer-mini.wasm) | 493 kB | mov, mp4, mkv, webm, m4v |

$3

For specific format support, customize the build:

1. Configure formats in Makefile:
`makefile
DEMUX_ARGS = \
--enable-demuxer=mov,mp4,m4a,3gp,3g2,mj2
`

2. Start Docker environment:
`bash


For ARM64 (Apple Silicon)

3. Build custom WASM:
`bash
npm run build:wasm
`

License

This project is licensed under the MIT License for the main codebase.
The lib/` directory contains FFmpeg-derived code under the LGPL License.