React Scroll Media

Production-ready, cinematic scroll sequences for React.

Zero scroll-jacking • Pure sticky positioning • 60fps performance

🌐 Live Demo • Installation • Usage • API • Examples

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🌟 Overview

react-scroll-media is a lightweight library for creating Apple-style "scrollytelling" image sequences. It maps scroll progress to image frames deterministically, using standard CSS sticky positioning for a native, jank-free feel.

Above: A 60fps scroll-driven sequence. The animation frame is tied 1:1 to the scroll position, allowing for instant scrubbing and pausing at any angle.

✨ Features

🚀 Native Performance

• Uses requestAnimationFrame for buttery smooth 60fps rendering
• No Scroll Jacking — We never hijack the scrollbar. It works with native scrolling
• CSS Sticky — Uses relatively positioned containers with sticky inner content

🖼️ Flexible Loading

• Manual — Pass an array of image URLs
• Pattern — Generate sequences like /img_{index}.jpg
• Manifest — Load sequences from a JSON manifest

🧠 Smart Memory Management

• Lazy Mode — Keeps only ±10 frames (configurable) in memory for huge sequences (800+ frames)
• Eager Mode — Preloads everything for maximum smoothness on smaller sequences
• Decoding — Uses img.decode() to prevent main-thread jank during painting

🛠️ Developer Experience

• Debug Overlay — Visualize progress and frame index in real-time
• Hooks — Exported useScrollSequence for custom UI implementations
• TypeScript — First-class type definitions
• SSR Safe — Works perfectly with Next.js / Remix / Gatsby
• A11y — Built-in support for prefers-reduced-motion and ARIA attributes
• Robust — Error boundaries and callbacks for image load failures

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🤔 When to Use This vs Video?

Feature	Video (<video>)	Scroll Sequence (react-scroll-media)
Quality	Compressed (artifacts)	✨ Lossless / Exact Frames (CRISP)
Transparency	Difficult (needs webm/hevc)	✨ Native PNG/WebP Transparency (Easy)
Scrubbing	Janky (keyframe dependency)	✨ 1:1 Instant Scrubbing
Mobile	Auto-play often blocked	✨ Works everywhere
File Size	✨ Small	Large (requires optimization/lazy loading)

💡 Use Scroll Sequence when you need perfect interaction, transparency, or crystal-clear product visuals (like Apple).

💡 Use Video for long, non-interactive backgrounds.

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📦 Installation

npm install react-scroll-media

or

yarn add react-scroll-media

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🚀 Usage

🎯 Basic Example

The simplest way to use it is with the ScrollSequence component.

import { ScrollSequence } from 'react-scroll-media';

const frames = [
  '/images/frame_01.jpg',
  '/images/frame_02.jpg',
  // ...
];

export default function MyPage() {
  return (
    <div style={{ height: '200vh' }}>
      <h1>Scroll Down</h1>
      
      <ScrollSequence
        source={{ type: 'manual', frames }}
        scrollLength="300vh" // Determines how long the sequence plays
      />
      
      <h1>Continue Scrolling</h1>
    </div>
  );
}

✨ Scrollytelling & Composition

You can nest components inside ScrollSequence. They will be placed in the sticky container and can react to the timeline.

📝 Animated Text (ScrollText)

Animate opacity and position based on scroll progress (0 to 1). Supports enter and exit phases.

import { ScrollSequence, ScrollText } from 'react-scroll-media';

<ScrollSequence source={...} scrollLength="400vh">
  
  {/* Fade In (0.1-0.2) -> Hold -> Fade Out (0.8-0.9) */}
  <ScrollText 
    start={0.1} 
    end={0.2} 
    exitStart={0.8}
    exitEnd={0.9}
    translateY={50} 
    className="my-text-overlay"
  >
    Cinematic Experience
  </ScrollText>

</ScrollSequence>

💬 Word Reveal (ScrollWordReveal)

Reveals text word-by-word as you scroll.

import { ScrollWordReveal } from 'react-scroll-media';

<ScrollWordReveal 
  text="Experience the smooth cinematic scroll."
  start={0.4}
  end={0.6}
  style={{ fontSize: '2rem', color: 'white' }}
/>

🔧 Advanced: Custom Hooks

For full control over the specialized UI, use the headless hooks.

useScrollSequence

Manages the canvas image controller.

import { useScrollSequence } from 'react-scroll-media';

const CustomScroller = () => {
  // ... setup refs
  const { containerRef, canvasRef, isLoaded } = useScrollSequence({ ... });
  // ... render custom structure
};

useScrollTimeline

Subscribe to the scroll timeline in any component.

import { useScrollTimeline } from 'react-scroll-media';

const MyComponent = () => {
  const { subscribe } = useScrollTimeline();

  // Subscribe to progress (0-1)
  useEffect(() => subscribe((progress) => {
    console.log('Progress:', progress);
  }), [subscribe]);

  return <div>...</div>;
};

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🎨 Image Fit Modes

The fit prop controls how images scale within the viewport, using the standard CSS object-fit property.

Mode	Description	Best Use Case
cover (Default)	Fills the screen, cropping edges if aspect ratios differ.	Full-screen background sequences.
contain	Shows the full image. Letterboxing (bars) may appear.	Product showcases where no part of the image should be cut off.
fill	Stretches to fill dimensions. Ignores aspect ratio.	Abstract patterns where distortion is acceptable.
none	Original size. No scaling.	Pixel-perfect displays when the wrapper matches image size.
scale-down	Smallest of none or contain.	Responsive layouts where images shouldn't upscale beyond native resolution.

---

⚙️ Configuration

ScrollSequence Props

Prop	Type	Default	Description
source	SequenceSource	Required	Defines where images come from.
scrollLength	string	"300vh"	Height of the container (animation duration).
memoryStrategy	"eager" | "lazy"	"eager"	Optimization strategy.
lazyBuffer	number	10	Number of frames to keep loaded in lazy mode.
fallback	ReactNode	null	Loading state component.
accessibilityLabel	string	"Scroll sequence"	ARIA label for the canvas. Example: "360 degree view of the product".
fit	"cover" | "contain" | "fill" | "none" | "scale-down"	"cover"	Determines how the image is resized to fit its container.
debug	boolean	false	Shows debug overlay.
onError	(error: Error) => void	undefined	Callback fired when an image fails to load or initialization errors occur.

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📊 Performance & Compatibility

📦 Bundle Size

Metric	Size
Minified	~23.72 kB
Gzipped	~7.11 kB

✨ Zero dependencies. Uses native Canvas API, no heavyweight libraries.

🌐 Browser Support

Browser	Status	Note
Chrome	✅	Full support (OffscreenCanvas enabled)
Firefox	✅	Full support
Safari	✅	Full support (Desktop & Mobile)
Edge	✅	Full support
IE11	❌	Not supported (Missing ES6/Canvas features)

♿ Accessibility (A11y)

• 🎹 Keyboard Navigation — Users can scrub through the sequence using standard keyboard controls (Arrow Keys, Spacebar, Page Up/Down) because it relies on native scrolling.

• 🔊 Screen Readers — Add accessibilityLabel to ScrollSequence to provide a description for the canvas. Canvas has role="img".

• 🎭 Reduced Motion — Automatically detects prefers-reduced-motion: reduce. If enabled, ScrollSequence will disable the scroll animation and display the fallback content (if provided) or simply freeze the first frame to prevent motion sickness.

💾 Memory Usage (Benchmarks)

Tested on 1080p frames.

Frames	Strategy	Memory	Recommendation
100	eager	30MB	Instant seeking, smooth.
500	eager	46MB	High RAM usage.
1000	eager	57MB	Very high RAM usage.
100	lazy	25MB	Low memory usage.
500	lazy	30MB	Low memory usage.
1000	lazy	45MB	⭐ Recommended. Kept flat constant.

🛡️ Error Handling & Fallbacks

Network errors are handled gracefully. You can provide a fallback UI that displays while images are loading or if they fail.

<ScrollSequence
  source={{ type: 'manifest', url: '/bad_url.json' }}
  fallback={<div className="error">Failed to load sequence</div>}
  onError={(e) => console.error("Sequence error:", e)}
/>

🚨 Error Boundaries

For robust production apps, wrap ScrollSequence in an Error Boundary to catch unexpected crashes:

class ErrorBoundary extends React.Component<
  { fallback: React.ReactNode, children: React.ReactNode }, 
  { hasError: boolean }
> {
  state = { hasError: false };
  
  static getDerivedStateFromError() { 
    return { hasError: true }; 
  }
  
  render() {
    if (this.state.hasError) return this.props.fallback;
    return this.props.children;
  }
}

// Usage
<ErrorBoundary fallback={<div>Something went wrong</div>}>
  <ScrollSequence source={...} /> 
</ErrorBoundary>

🔄 Multi-Instance & Nested Scroll

react-scroll-media automatically handles multiple instances on the same page. Each instance:

1. Registers with a shared RAF loop (singleton) for optimal performance.
2. Calculates its own progress independently.
3. Should have a unique scrollLength or container setup.

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🏗️ Architecture

📂 SequenceSource Options

1. Manual Mode (Pass array directly)

{
  type: 'manual',
  frames: ['/img/1.jpg', '/img/2.jpg']
}

2. Pattern Mode (Generate URLs)

{
  type: 'pattern',
  url: '/assets/sequence_{index}.jpg', // {index} is replaced
  start: 1,    // Start index
  end: 100,    // End index
  pad: 4       // Zero padding (e.g. 1 -> 0001)
}

3. Manifest Mode (Fetch JSON)

{
  type: 'manifest',
  url: '/sequence.json' 
}

// JSON format: { "frames": ["url1", "url2"] } OR pattern config

💡 Note: Manifests are cached in memory by URL. To force a refresh, append a query param (e.g. ?v=2).

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🎨 How it Works (The "Sticky" Technique)

Unlike libraries that use position: fixed or JS-based scroll locking (which breaks refreshing and feels unnatural), we use CSS Sticky Positioning.

Technical Demo: This visualization shows the direct correlation between the scrollbar position and the rendered frame. The component calculates the exact frame index based on the percentage of the container scrolled, ensuring perfect synchronization without "scroll jacking".

🔧 Technical Breakdown

1. Container (relative) — This element has the height you specify (e.g., 300vh). It occupies space in the document flow.

2. Sticky Wrapper (sticky) — Inside the container, we place a div that is 100vh tall and sticky at top: 0.

3. Canvas — The <canvas> sits inside the sticky wrapper.

4. Math — As you scroll the container, the sticky wrapper stays pinned to the viewport. We calculate:

progress = -containerRect.top / (containerHeight - viewportHeight)

This gives a precise 0.0 to 1.0 value tied to the pixel position of the scrollbar. This value is then mapped to the corresponding frame index:

frameIndex = Math.floor(progress * (totalFrames - 1))

This approach ensures:

• Zero Jitter: The canvas position is handled by the browser's compositor thread (CSS Sticky).
• Native Feel: Momentum scrolling works perfectly on touchpads and mobile.
• Exact Sync: The frame updates are synchronized with the scroll position in a requestAnimationFrame loop.

💡 Memory Strategy

• "eager" (Default) — Best for sequences < 200 frames. Preloads all images into HTMLImageElement instances. Instant seeking, smooth playback. High memory usage.

• "lazy" — Best for long sequences (500+ frames). Only keeps the current frame and its neighbors in memory. Saves RAM, prevents crashes.

  • Buffer size defaults to ±10 frames but can be customized via lazyBuffer.

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🐛 Debugging

Enable the debug overlay to inspect your sequence in production:

<ScrollSequence 
  source={...} 
  debug={true} 
/>

Output:

Progress: 0.45
Frame: 45 / 100

This overlay is updated directly via DOM manipulation (bypassing React renders) for zero overhead.

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🔒 Security

react-scroll-media prioritizes security and follows best practices for client-side rendering libraries.

Network Access

When using Manifest Mode (source.type === 'manifest'), the library makes network requests to fetch your manifest configuration. For security recommendations and best practices, see our SECURITY.md document.

Key Points:

• ✅ Network access is optional (only when using manifest mode)
• ✅ No external dependencies or third-party integrations
• ✅ All processing happens client-side
• ✅ No data collection or telemetry

Built-in Security Hardening (v1.0.5+):

• 🔐 HTTPS enforcement — HTTP manifest URLs are rejected
• 🔐 Credential isolation — credentials: 'omit' prevents cookie/auth leakage
• 🔐 Referrer protection — referrerPolicy: 'no-referrer' prevents page URL leakage
• 🔐 Response size limit — 1MB max to prevent memory exhaustion
• 🔐 Frame URL whitelist — Only http:/https: and relative paths allowed; //evil.com rejected
• 🔐 Frame count cap — Default 2000, ceiling 8000, configurable via REACT_SCROLL_MEDIA_MAX_FRAMES
• 🔐 Cache size limit — 50 entry cap with automatic eviction
• 🔐 Timeout protection — 10-second abort on slow responses
• 🔐 Response validation — Content-type + structure checks

Quick Security Tips:

• Use HTTPS for all manifest URLs
• Only load manifests from trusted sources
• Use Manual or Pattern modes for sensitive environments
• Implement Content Security Policy headers

👉 Full Security Policy →

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📄 License

MIT © 2026 Thanniru Sai Teja

Made with ❤️ for the React community

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