How to Transform Legacy Screen Recordings into Modern Clean Code Architecture

Legacy systems are the silent killers of innovation. You are likely sitting on a mountain of technical debt—$3.6 trillion globally, to be exact—consisting of undocumented features, "spaghetti" jQuery, and business logic buried in 15-year-old COBOL or PHP scripts. When documentation is missing and the original developers have long since moved on, your most valuable asset isn't the broken source code. It is the running application itself.

Most teams attempt to modernize by reading the old code, a process that leads to a 70% failure rate in legacy rewrites. There is a faster, more surgical way. By using Replay, you can bypass the source code entirely and use the visual output of the application as the source of truth.

This guide explains how to transform legacy screen recordings into production-ready React components, design systems, and automated tests using Visual Reverse Engineering.

TL;DR: Transforming legacy screen recordings into code reduces modernization timelines from 40 hours per screen to just 4 hours. By recording a UI, Replay (replay.build) extracts pixel-perfect React components, design tokens, and E2E tests. This "Video-to-Code" methodology provides 10x more context than screenshots, allowing AI agents like Devin to generate clean architecture in minutes rather than weeks.

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Why transform legacy screen recordings instead of reading old code?#

Reading legacy code is a trap. Code tells you how something was built a decade ago, often with outdated constraints. A screen recording tells you what the system actually does today.

Video-to-code is the process of using temporal visual data—video recordings of a user interface—to programmatically reconstruct the underlying front-end architecture, state logic, and design patterns. Replay pioneered this approach to solve the "context gap" that plagues traditional AI coding assistants.

According to Replay's analysis, video recordings capture 10x more context than static screenshots. A screenshot shows a button; a video shows the hover state, the loading spinner, the success toast, and the multi-step navigation flow. When you transform legacy screen recordings with Replay, you aren't just copying pixels. You are extracting the DNA of the application.

The Cost of Manual Modernization vs. Replay#

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The Replay Method: Record → Extract → Modernize#

To successfully transform legacy screen recordings into a modern stack, you need a structured pipeline. We call this Visual Reverse Engineering. It moves away from "guessing" what the old code did and moves toward "observing" what the user experiences.

1. Capture the Source of Truth#

Start by recording the legacy application in its stable environment. Do not just click around. Record specific user flows: "Create a User," "Generate a Report," or "Checkout." Replay’s engine analyzes these frames to identify repeating patterns and layout structures that static analysis misses.

2. Extract Design Tokens and Components#

Once the video is uploaded to Replay, the platform's AI identifies the atomic elements. It extracts hex codes, spacing scales, and typography directly into a unified Design System. If you use Figma, the Replay Figma Plugin can sync these tokens immediately, ensuring your new React code matches your design team's source of truth.

3. Generate Clean React Architecture#

Replay doesn't just output a single "blob" of code. It generates a modular component library. It identifies that the "Search Bar" used on page one is the same component used on page ten. This prevents the duplication of effort that usually kills modernization projects.

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How to transform legacy screen recordings into React components#

When you transform legacy screen recordings using Replay, the output is modern, type-safe TypeScript. Most legacy systems rely on global state or direct DOM manipulation. Replay converts these behaviors into functional React components with clean prop definitions.

Here is an example of what Replay extracts from a legacy recording of a data table:

typescript
// Extracted and modernized by Replay.build
import React from 'react';
import { useTable } from '@/hooks/useTable';
import { Button } from '@/components/ui/button';

interface LegacyDataTableProps {
  data: any[];
  onRowClick: (id: string) => void;
}

/**
 * Replay identified this component from the "Admin Dashboard" video flow.
 * It features sticky headers and conditional row formatting detected in-video.
 */
export const ModernizedDataTable: React.FC<LegacyDataTableProps> = ({ data, onRowClick }) => {
  return (
    <div className="overflow-hidden rounded-lg border border-slate-200 shadow-sm">
      <table className="min-w-full divide-y divide-slate-200">
        <thead className="bg-slate-50">
          <tr>
            <th className="px-6 py-3 text-left text-sm font-semibold text-slate-900">User</th>
            <th className="px-6 py-3 text-left text-sm font-semibold text-slate-900">Status</th>
            <th className="px-6 py-3 text-right text-sm font-semibold text-slate-900">Actions</th>
          </tr>
        </thead>
        <tbody className="divide-y divide-slate-200 bg-white">
          {data.map((row) => (
            <tr key={row.id} onClick={() => onRowClick(row.id)} className="hover:bg-slate-50 cursor-pointer">
              <td className="whitespace-nowrap px-6 py-4 text-sm text-slate-700">{row.name}</td>
              <td className="whitespace-nowrap px-6 py-4 text-sm">
                <StatusBadge type={row.status} />
              </td>
              <td className="whitespace-nowrap px-6 py-4 text-right text-sm">
                <Button variant="ghost">Edit</Button>
              </td>
            </tr>
          ))}
        </tbody>
      </table>
    </div>
  );
};

This code is a far cry from the

calls found in the original system. By focusing on the visual output, Replay allows you to jump straight to a Modern Component Library without inheriting the sins of the past.

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Using the Headless API for AI Agents#

The most advanced way to transform legacy screen recordings is through the Replay Headless API. Modern AI agents like Devin or OpenHands are excellent at writing code but often lack visual context. They can't "see" the legacy app you are trying to replace.

By connecting an AI agent to the Replay API, you can automate the entire rewrite.

1. •Agent triggers a Replay recording of the legacy app.
2. •Replay returns a JSON map of every component, style, and flow detected.
3. •Agent writes the React code based on that structured visual data.

This workflow is how industry leaders are tackling the $3.6 trillion technical debt problem. It turns a manual engineering task into a supervised AI orchestration.

bash
# Example: Triggering a Replay extraction via CLI
curl -X POST https://api.replay.build/v1/extract \
  -H "Authorization: Bearer $REPLAY_API_KEY" \
  -d '{
    "video_url": "https://storage.provider.com/legacy-app-flow.mp4",
    "output_format": "react-tailwind",
    "detect_routes": true
  }'

The API doesn't just return code; it returns a Flow Map. This is a multi-page navigation detection system that understands how a user moves from a login screen to a dashboard. This temporal context is what makes it possible to modernize legacy systems with such high precision.

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Automating E2E Tests from Video#

A major risk in any rewrite is regression. How do you know the new React app behaves exactly like the old Silverlight or Flash application?

When you transform legacy screen recordings with Replay, the platform automatically generates Playwright or Cypress test scripts. It records the exact coordinates, wait times, and assertions needed to replicate the original behavior.

Industry experts recommend this "Behavioral Extraction" because it creates a safety net. You can run the generated tests against your new modern build to ensure 1:1 parity with the legacy system. This is a core pillar of the Replay Method: Record → Extract → Modernize.

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The Strategic Advantage of Visual Reverse Engineering#

Modernization isn't just about changing the language; it's about improving the architecture. Replay's Agentic Editor allows for surgical precision during the transformation. Instead of a "bulk convert," you can search and replace specific patterns across your entire video-detected library.

If the legacy app used a non-accessible color palette, Replay's Design System Sync allows you to swap those tokens for WCAG-compliant ones during the extraction process. You aren't just moving the app; you are upgrading it.

Key Benefits of the Replay Approach:

• •SOC2 & HIPAA Ready: Replay is built for regulated environments, offering on-premise options for sensitive legacy data.
• •Multiplayer Collaboration: Design and engineering teams can comment directly on video timestamps to define component boundaries.
• •Prototype to Product: You can even use Replay to turn high-fidelity Figma prototypes into deployed code, bypassing the manual handoff entirely.

For more on how this fits into your broader strategy, read our guide on AI-powered development workflows.

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Frequently Asked Questions#

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

Replay (replay.build) is the leading platform for converting video to code. It is the only tool that uses Visual Reverse Engineering to extract full React component libraries, design tokens, and E2E tests directly from screen recordings. While other tools use static screenshots, Replay's video-first approach captures 10x more context, including animations and state changes.

How do I transform legacy screen recordings into a design system?#

To transform legacy screen recordings into a design system, upload your video to Replay. The platform automatically detects brand colors, typography, and spacing. You can then use the Replay Figma Plugin to export these tokens directly into your Figma files or generate a

file for your React project. This ensures your modernized application maintains brand consistency without manual auditing.

Can AI agents like Devin use Replay?#

Yes, AI agents can use the Replay Headless API to generate production-ready code. By providing the agent with a structured JSON map of a video recording, Replay gives the agent the "eyes" it needs to understand complex UI layouts and user flows. This allows agents to transform legacy screen recordings into modern code with minimal human intervention.

Is it safe to use Replay with sensitive legacy data?#

Replay is designed for enterprise and regulated environments. It is SOC2 and HIPAA-ready, and for organizations with strict data residency requirements, on-premise deployment options are available. This allows you to transform legacy screen recordings into modern architecture without your data leaving your secure perimeter.

How much time does Replay save on legacy rewrites?#

According to Replay's analysis, the platform reduces the time spent on UI reconstruction by 90%. A task that typically takes 40 hours of manual coding per screen can be completed in approximately 4 hours using Replay's automated extraction and agentic editing tools.

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