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Readme

🎨 magic-webp

Fast WebP image processing in the browser using WebAssembly

Process WebP images (static and animated) directly in the browser with native performance. Built on top of Google's libwebp compiled to WebAssembly.

🎮 Live Demo • Features • Installation • Quick Start • API • Development

✨ Features

🖼️ WebP Support — Both static and animated WebP images
✂️ Crop — Extract regions (preserves animation frames)
📐 Resize — Multiple modes: cover, contain, fill, inside, outside
🎚️ Quality Control — Adjustable output quality (0-100, lossless)
🚀 Fast — Native libwebp with SIMD optimizations (5-10x faster)
🌐 Browser-first — No server required, runs entirely client-side
🔒 Thread-safe — Automatic operation queuing for concurrent calls
📦 Zero dependencies — Pure WebAssembly, no external libraries

📦 Installation

npm install magic-webp
# or
pnpm add magic-webp
# or
yarn add magic-webp

🚀 Quick Start

Recommended: Using Web Worker (Non-blocking UI)

Step 1: Copy worker.js to your public folder

# Copy from node_modules
cp node_modules/magic-webp/src-js/worker.ts public/worker.js

# Or download from GitHub
# https://github.com/medzhidov/magic-webp/blob/master/src-js/worker.ts

Step 2: Use the simple API

import { MagicWebpWorker } from 'magic-webp';

// Initialize worker
const webp = new MagicWebpWorker('/worker.js');

// Load image
const file = document.querySelector('input[type="file"]').files[0];
await webp.load(file);

// Resize (returns Blob directly!)
const blob = await webp.resize(400, 400, { mode: 'cover', quality: 75 });  // 75 = balanced (recommended)

// Use the result
const url = URL.createObjectURL(blob);
document.querySelector('img').src = url;

// Clean up when done
webp.terminate();

That's it! No manual Worker management, no message passing, just simple async calls.

✨ Benefits: Non-blocking UI, better performance, automatic request queuing

⚠️ Important: Web Worker Requirements

1. Same-Origin Policy

Worker file must be served from the same domain as your app
❌ Won't work: new MagicWebpWorker('https://cdn.example.com/worker.js')
✅ Works: new MagicWebpWorker('/worker.js') (same domain)

2. Module Type

Worker must be loaded as ES module (type: 'module')
Already handled by MagicWebpWorker constructor

3. CORS Headers (if serving from different path)

If worker is on subdomain, ensure proper CORS headers:
```
Access-Control-Allow-Origin: *
```

4. File Serving

Worker file must be accessible via HTTP/HTTPS
❌ Won't work with file:// protocol (local files)
✅ Use local dev server: npx serve or python -m http.server

5. Build Tools

Vite: Worker is automatically bundled

const webp = new MagicWebpWorker(
  new URL('./worker.ts', import.meta.url).href
);

Webpack: Use worker-loader or native Worker support
Create React App: Place worker in public/ folder

Common Issues:

// ❌ WRONG: Cross-origin
const webp = new MagicWebpWorker('https://cdn.com/worker.js');
// Error: Failed to construct 'Worker': Script at '...' cannot be accessed from origin '...'

// ✅ CORRECT: Same origin
const webp = new MagicWebpWorker('/worker.js');

// ✅ CORRECT: Relative path
const webp = new MagicWebpWorker('./worker.js');

// ✅ CORRECT: Vite/Webpack (bundled)
const webp = new MagicWebpWorker(
  new URL('./worker.ts', import.meta.url).href
);

Alternative: Main Thread (Simpler, but blocks UI)

import { MagicWebp } from 'magic-webp';

const file = document.querySelector('input[type="file"]').files[0];
const img = await MagicWebp.fromBlob(file);
const resized = await img.resize(400, 400, { mode: 'cover', quality: 75 });  // 75 = balanced
const blob = resized.toBlob();

⚠️ Note: Main thread usage blocks the UI during processing. Use MagicWebpWorker for production apps.

📖 API

MagicWebpWorker (Recommended)

import { MagicWebpWorker } from 'magic-webp';

// Initialize
const webp = new MagicWebpWorker('/worker.js');

// Load image
await webp.load(file);  // File or Blob

// Get dimensions
console.log(webp.width, webp.height);

// Crop
const blob = await webp.crop(x, y, width, height, quality);

// Resize
const blob = await webp.resize(width, height, { mode, position, quality });

// Clean up
webp.terminate();

MagicWebp (Main Thread)

import { MagicWebp } from 'magic-webp';

// Load from File/Blob
const img = await MagicWebp.fromBlob(blob);
const img = await MagicWebp.fromFile(file);

// Load from URL
const img = await MagicWebp.fromUrl('https://example.com/image.webp');

// Load from Uint8Array
const img = await MagicWebp.fromBytes(uint8Array);

Transformations

All transformation methods are async and return Promise<MagicWebp>.

Crop

// Crop 200x200 region starting at (50, 50)
const cropped = await img.crop(50, 50, 200, 200, quality);

Resize

// Cover - fills dimensions, crops excess (default)
const cover = await img.resize(400, 400, { mode: 'cover' });

// Contain - fits inside dimensions, preserves aspect ratio
const contain = await img.resize(400, 400, { mode: 'contain' });

// Fill - stretches to exact dimensions (may distort)
const fill = await img.resize(400, 400, { mode: 'fill' });

// Inside - like contain, but never enlarges
const inside = await img.resize(400, 400, { mode: 'inside' });

// Outside - like cover, but never reduces
const outside = await img.resize(400, 400, { mode: 'outside' });

// With position (for cover/outside modes)
const banner = await img.resize(1200, 400, {
  mode: 'cover',
  position: 'top',  // 'center', 'top', 'bottom', 'left', 'right', etc.
  quality: 75       // 0-100, default 75 (balanced - recommended)
});

Output

// As Blob
const blob = img.toBlob();

// As Uint8Array
const bytes = img.toBytes();

// As Data URL
const dataUrl = await img.toDataUrl();

// As Object URL
const objectUrl = img.toObjectUrl();

Resize Options

interface ResizeOptions {
  mode?: 'cover' | 'contain' | 'fill' | 'inside' | 'outside';  // default: 'cover'
  position?: 'center' | 'top' | 'bottom' | 'left' | 'right' |  // default: 'center'
             'top-left' | 'top-right' | 'bottom-left' | 'bottom-right';
  quality?: number;  // 0-100, default: 75 (balanced)
}

💡 Quality Recommendations:

Quality	File Size	Visual Quality	Use Case	Recommended For
60-70	Smallest	Visible artifacts	Thumbnails, previews	Low priority images
75-85	Medium	Good balance	Most web images	✅ Default (75)
90-95	Large	Excellent	Important photos	Hero images, portfolios
100	Largest	Perfect (lossless)	Archival, editing	When quality is critical

Quality Recommendations

60-70: High compression, visible artifacts (good for thumbnails)
75-85: Balanced quality/size (recommended for most cases)
90-95: High quality, minimal artifacts (for important images)
100: Lossless, largest file size (perfect quality preservation)

Supported Formats

Input:

✅ Static WebP
✅ Animated WebP (multi-frame)

Output:

✅ Static WebP (from static input)
✅ Animated WebP (from animated input, preserves all frames and timing)

Note: All operations (crop, resize) work on both static and animated WebP. For animated images, each frame is processed individually while preserving animation metadata (timing, loop count, etc.).

💡 Examples

With Worker (Recommended)

import { MagicWebpWorker } from 'magic-webp';

const webp = new MagicWebpWorker('/worker.js');
await webp.load(file);

// Avatar - square 200x200, centered (high quality for profile pics)
const avatar = await webp.resize(200, 200, { mode: 'cover', quality: 85 });

// Product preview - fit inside 300x300 (balanced quality)
const preview = await webp.resize(300, 300, { mode: 'contain', quality: 75 });

// Banner - 1200x400, crop from top (high quality for hero images)
const banner = await webp.resize(1200, 400, {
  mode: 'cover',
  position: 'top',
  quality: 90
});

// Thumbnail - never enlarge (lower quality for small images)
const thumb = await webp.resize(150, 150, { mode: 'inside', quality: 65 });

// Crop specific region (balanced quality)
const cropped = await webp.crop(50, 50, 200, 200, 75);

webp.terminate();

With Main Thread

import { MagicWebp } from 'magic-webp';

const img = await MagicWebp.fromBlob(file);

// Chaining operations
const result = await img
  .crop(100, 100, 400, 400)
  .then(cropped => cropped.resize(200, 200, { mode: 'contain' }));

// Concurrent processing (automatically queued)
const [avatar, thumb, banner] = await Promise.all([
  img.resize(200, 200, { mode: 'cover' }),
  img.resize(150, 150, { mode: 'inside' }),
  img.resize(1200, 400, { mode: 'cover', position: 'top' })
]);

Animated WebP

// Works with both static and animated WebP
// For animated images, all frames are processed while preserving timing

const webp = new MagicWebpWorker('/worker.js');
await webp.load(animatedWebpFile);

// All frames will be resized
const resized = await webp.resize(400, 400, { mode: 'cover' });

🔧 Advanced Usage

Memory Management

// Worker automatically manages memory, but you should terminate when done
const webp = new MagicWebpWorker('/worker.js');

// ... use worker ...

// Clean up when component unmounts or app closes
webp.terminate();

Error Handling

const webp = new MagicWebpWorker('/worker.js');

try {
  await webp.load(file);
  const blob = await webp.resize(400, 400, { mode: 'cover' });
} catch (error) {
  console.error('Processing failed:', error);
  // Handle error (show message to user, retry, etc.)
}

Multiple Workers (Parallel Processing)

// Create multiple workers for parallel processing
const workers = [
  new MagicWebpWorker('/worker.js'),
  new MagicWebpWorker('/worker.js'),
  new MagicWebpWorker('/worker.js')
];

// Process multiple images in parallel
const results = await Promise.all(
  files.map((file, i) => {
    const worker = workers[i % workers.length];
    return worker.load(file).then(() =>
      worker.resize(400, 400, { mode: 'cover' })
    );
  })
);

// Clean up
workers.forEach(w => w.terminate());

Browser Compatibility

✅ Chrome 80+
✅ Firefox 79+
✅ Safari 14+
✅ Edge 80+
❌ IE 11 (no WebAssembly support)

Check before using:

if (typeof WebAssembly === 'undefined') {
  console.error('WebAssembly not supported');
  // Fallback to server-side processing
}

if (typeof Worker === 'undefined') {
  console.warn('Web Workers not supported, using main thread');
  // Use MagicWebp instead of MagicWebpWorker
}

🛠️ Development

Prerequisites

Node.js 18+
pnpm (recommended) or npm
Emscripten SDK (automatically installed)

Setup

# Clone repository
git clone https://github.com/medzhidov/magic-webp.git
cd magic-webp

# Install dependencies
pnpm install

# Build WASM module
pnpm build:wasm

# Run demo
pnpm demo:watch

Project Structure

magic-webp/
├── src-c/           # C source code
│   ├── animation.c  # WebP animation processing
│   └── magic_webp.c # Core functions
├── src-js/          # TypeScript API
│   ├── index.ts     # Main API
│   └── *.test.ts    # Tests
├── demo/            # Demo application
│   ├── index.html
│   ├── main.ts
│   └── worker.ts    # Web Worker for processing
├── tests/           # Native C tests
├── libwebp/         # Google's libwebp (submodule)
└── pkg/             # Built WASM output

Build Commands

# Build WASM module
pnpm build:wasm

# Run TypeScript tests
pnpm test

# Run native C tests
pnpm test:native

# Run demo (dev server)
pnpm demo:watch

# Build demo for production
pnpm demo:build

How It Works

C Code (src-c/) - Uses libwebp's WebPPicture API for high-quality image processing
Animation Support - Processes each frame individually, preserving timing and metadata
Emscripten - Compiles C code to WebAssembly with SIMD optimizations
TypeScript API (src-js/) - Provides clean, type-safe interface
Operation Queue - Ensures thread-safety by serializing WASM calls
Web Worker (demo) - Keeps UI responsive during processing

Performance

5-10x faster than pure JavaScript implementations
SIMD optimizations (SSE2, NEON) for resize operations
Optimized cover mode - single pass resize+crop (2x faster)
Minimal memory - in-place operations where possible

📋 Quick Reference

Resize Modes

Mode	Behavior	Use Case
`cover`	Fills dimensions, crops excess	Avatars, thumbnails
`contain`	Fits inside, preserves aspect	Product images, previews
`fill`	Stretches to exact size	Backgrounds (may distort)
`inside`	Like contain, never enlarges	Thumbnails of small images
`outside`	Like cover, never reduces	Cropping large images

Position Options (for cover/outside)

Position	Description
`center`	Center of image (default)
`top`	Top center
`bottom`	Bottom center
`left`	Left center
`right`	Right center
`top-left`	Top left corner
`top-right`	Top right corner
`bottom-left`	Bottom left corner
`bottom-right`	Bottom right corner

Quality Guidelines

Quality	File Size	Visual Quality	Use Case
60-70	Smallest	Visible artifacts	Thumbnails, previews
75-85	Medium	Good balance	Most web images
90-95	Large	Excellent	Important images, photos
100	Largest	Perfect (lossless)	Archival, editing

📄 License

🙏 Acknowledgments

libwebp - Google's WebP library
Emscripten - C/C++ to WebAssembly compiler

Made with ❤️ for the web