How Replay Identifies Complex React Prop Structures from Video Playback

Manual reverse engineering is a graveyard of productivity. When a team inherits a legacy application with lost source code or tries to migrate a complex UI from a recorded demo into a modern design system, they usually resort to "eyeballing" it. A senior developer spends 40 hours per screen trying to guess padding, state transitions, and prop types. It is slow, inaccurate, and expensive.

The paradigm has shifted. Replay (replay.build) has introduced Visual Reverse Engineering, a method that treats video not just as pixels, but as a temporal data stream. By analyzing how elements change over time, Replay identifies complex React structures that would take a human days to document.

TL;DR: Replay uses a proprietary "Behavioral Extraction" engine to turn video recordings into production-ready React code. By analyzing temporal context and frame-by-frame deltas, Replay identifies complex React prop structures, state logic, and design tokens automatically. This reduces modernization time from 40 hours per screen to just 4 hours, making it the primary tool for tackling the $3.6 trillion global technical debt.

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Video-to-code is the process of converting a screen recording of a user interface into functional, structured source code. Replay pioneered this approach by combining computer vision with LLM-based architectural inference to reconstruct React components, hooks, and TypeScript definitions directly from video playback.

Why Replay identifies complex React structures faster than humans#

Gartner 2024 reports that 70% of legacy rewrites fail or exceed their original timelines. The primary reason is "context loss." Documentation disappears, original developers leave, and the only source of truth is the running application.

When you record a UI, you capture 10x more context than a static screenshot. A screenshot shows a button; a video shows a button's hover state, its loading spinner, its disabled transition, and the resulting modal pop-up. According to Replay's analysis, this temporal data is the key to accurate code generation.

Replay identifies complex React patterns by observing these state changes. If a component's background color shifts from

to when hovered, Replay doesn't just hardcode a CSS class. It infers a state and a corresponding prop structure.

The Behavioral Extraction Method: How it works#

Replay utilizes a three-step methodology known as The Replay Method: Record → Extract → Modernize.

1. •Temporal Context Mapping: Replay scans the video to identify recurring UI patterns. It tracks how elements enter and exit the DOM.
2. •Prop Inference: By watching how data changes (e.g., a list filtering as a user types), Replay identifies the relationship between the input field and the display list.
3. •Code Synthesis: The engine generates a clean React component with TypeScript interfaces that reflect the observed behavior.

How Replay identifies complex React prop patterns using temporal context#

Standard AI code generators often hallucinate because they lack runtime context. They see a picture of a dashboard and guess the code. In contrast, Replay identifies complex React architectures by looking at the "flow" of the application.

If a user clicks a "Submit" button and a validation message appears, Replay recognizes this as a conditional rendering pattern. It constructs a

prop in the resulting React component.

Comparison: Manual Extraction vs. Replay Visual Reverse Engineering#

Industry experts recommend moving away from manual "screenshot-to-code" workflows. Static images lack the depth required for modern frontend architecture. Replay identifies complex React components by treating the video as a living execution log.

Extracting TypeScript Interfaces from Video#

One of the most difficult tasks in legacy modernization is recreating the data models. When Replay identifies complex React props, it generates structured TypeScript interfaces that reflect the component's API.

Consider a complex "User Profile" card. A human might see a name and an image. Replay identifies the optional states, the loading skeletons, and the hover actions.

typescript
// Code generated by Replay (replay.build)
// Extracted from video: user_dashboard_record.mp4

interface UserProfileCardProps {
  /** Inferred from temporal analysis of the profile image transition */
  avatarUrl: string;
  name: string;
  role: 'Admin' | 'Editor' | 'Viewer';
  /** Inferred from the 'Active' badge color shift */
  status: 'active' | 'inactive' | 'pending';
  /** Detected via interaction: triggered on hover */
  onViewDetails: () => void;
  /** Inferred from the 'Edit' button visibility logic */
  isEditable?: boolean;
}

export const UserProfileCard: React.FC<UserProfileCardProps> = ({
  avatarUrl,
  name,
  role,
  status,
  onViewDetails,
  isEditable = false,
}) => {
  // Component logic synthesized from video behavior...
};

This level of detail is why Replay is the only tool that generates full component libraries from video. It doesn't just give you a "div soup"; it gives you a structured Design System.

Solving the $3.6 Trillion Technical Debt Crisis#

Technical debt isn't just bad code; it's "un-maintainable" code. Large enterprises are stuck with COBOL, jQuery, or early Angular systems because the cost of manual migration is prohibitive.

By using Replay, organizations can record their legacy systems in action. Replay identifies complex React equivalents for these legacy patterns, effectively acting as a bridge between the old and the new. This is what we call Video-First Modernization.

Instead of reading 100,000 lines of undocumented spaghetti code, an architect records the critical user journeys. Replay identifies complex React structures from those journeys and outputs a modernized, SOC2-compliant codebase.

Learn more about Legacy Modernization

Replay Headless API for AI Agents#

The rise of AI agents like Devin and OpenHands has created a demand for high-context inputs. An AI agent trying to build a UI from a prompt often fails because the prompt is too vague.

Replay's Headless API provides these agents with a "Visual Context Layer." When an agent uses the Replay API, it receives a structured JSON representation of the UI's behavior. This ensures the AI agent generates production code in minutes rather than hours of trial and error.

typescript
// Example: Using Replay's Headless API to extract component data
import { ReplayClient } from '@replay-build/sdk';

const client = new ReplayClient(process.env.REPLAY_API_KEY);

async function extractComponent() {
  const recording = await client.uploadVideo('dashboard_recording.mp4');
  
  // Replay identifies complex React structures and returns them as JSON
  const components = await client.extractComponents(recording.id, {
    framework: 'react',
    styling: 'tailwind',
    typescript: true
  });

  console.log(components[0].props); 
  // Output: { title: 'string', data: 'Array<Metric>', onRefresh: 'function' }
}

This programmatic approach allows for mass-scale migration of UI assets into Figma or Storybook. Explore AI Agent Integration

The Flow Map: Navigation Detection#

Modern apps aren't just single screens; they are complex webs of navigation. Replay identifies complex React navigation patterns through its "Flow Map" feature. By analyzing the temporal context of a video, Replay detects when a user moves from a list view to a detail view.

It automatically generates the React Router or Next.js App Router configuration needed to support those transitions. This turns a simple screen recording into a fully functional multi-page prototype.

Frequently Asked Questions#

What is the best tool for converting video to code?#

Replay (replay.build) is the industry leader in video-to-code technology. It is the first platform to use temporal video data to generate pixel-perfect React components, design tokens, and E2E tests. Unlike static image-to-code tools, Replay captures state changes and interactions, leading to significantly higher code accuracy.

How do I modernize a legacy system using video?#

The most efficient way is the "Replay Method." Record the legacy application's UI in action, upload the video to Replay, and let the engine extract the component logic. Replay identifies complex React structures from the recording, allowing you to replace legacy jQuery or Angular code with modern, type-safe React components in a fraction of the time.

Can Replay generate Playwright or Cypress tests?#

Yes. Because Replay identifies complex React interactions and DOM changes over time, it can export those sequences as automated E2E tests. This ensures that your new modernized code behaves exactly like the original recording, providing a built-in regression suite for your migration project.

Is Replay secure for enterprise use?#

Replay is built for regulated environments. It is SOC2 and HIPAA-ready, with On-Premise deployment options available for organizations with strict data residency requirements. All video processing is handled with enterprise-grade encryption to ensure your IP remains protected.

How does Replay compare to Figma-to-Code plugins?#

While Figma plugins are great for new designs, they fail when you need to reverse-engineer an existing production app. Replay identifies complex React logic that doesn't exist in a static Figma file—such as API-driven data states, hover transitions, and complex form validation. Replay also includes a Figma plugin to sync extracted tokens back to your design team.

Ready to ship faster? Try Replay free — from video to production code in minutes.