How to Extract Reusable UI Components from Legacy Screencasts with Replay

Legacy codebases are liabilities disguised as assets. Global technical debt has ballooned to a staggering $3.6 trillion, and the cost of maintaining these systems consumes nearly 70% of IT budgets. When you are tasked with modernizing a sprawling enterprise application, you usually face two bad options: a "big bang" rewrite that has a 70% failure rate or a manual component-by-component migration that takes years.

Replay (replay.build) introduces a third path. Instead of digging through thousands of lines of undocumented jQuery or COBOL, you record the application in action. Replay uses Visual Reverse Engineering to transform these video recordings into production-ready React components, design tokens, and end-to-end tests.

TL;DR: Replay is the first video-to-code platform designed to extract reusable components from legacy screencasts. By capturing 10x more context than static screenshots, Replay reduces the time to modernize a single screen from 40 hours to just 4 hours. It offers a Headless API for AI agents, SOC2 compliance for enterprise security, and seamless sync with Figma and Storybook.

---

Why video is the superior medium to extract reusable components from#

Most developers try to modernize UI by taking screenshots and feeding them into LLMs. This fails because a screenshot is a flat, static representation of a dynamic state. It misses the hover effects, the transition timings, the data-loading skeletons, and the complex branching logic of a real-world application.

Video-to-code is the process of using temporal video data to reconstruct the underlying logic and styling of a user interface. Replay pioneered this approach because video provides the "temporal context" necessary to understand how a component behaves, not just how it looks.

According to Replay’s analysis, video recordings capture 10x more context than static images. When you use Replay to extract reusable components from a recording, the AI sees the component in motion. It identifies that a button isn't just a

tag, but a complex unit with specific padding, border-radius, and hex codes that must match your new Design System.

The Problem with Manual Extraction#

Manual extraction is a recipe for burnout. A senior engineer spends roughly 40 hours per screen identifying styles, mapping logic, and writing unit tests. With Replay, that same engineer can record a 30-second walkthrough and generate a pixel-perfect React component in minutes.

---

How to extract reusable components from legacy systems using the Replay Method#

Modernization isn't just about code; it’s about workflow. Replay utilizes a proprietary workflow known as The Replay Method: Record → Extract → Modernize. This methodology ensures that the generated code isn't just "AI-flavored" junk, but clean, maintainable TypeScript that fits your existing architecture.

Step 1: Record the Legacy UI#

You don't need access to the original source code. If you can run the application in a browser, you can modernize it. Use the Replay recorder to capture the specific user flows—login sequences, data tables, or complex dashboards.

Step 2: Extract Reusable Components#

Once the video is uploaded to replay.build, the platform’s Agentic Editor goes to work. It identifies recurring patterns across the video frames. It notices that the sidebar navigation on page one is the same component used on page ten, even if the data inside it changes.

Step 3: Modernize and Sync#

Replay doesn't just give you a raw dump of code. It extracts brand tokens—colors, spacing, typography—and maps them to your new Design System. If you have an existing Figma file, the Replay Figma Plugin can sync these tokens directly, ensuring the code matches the design intent perfectly.

---

Comparing manual modernization vs. Replay-driven extraction#

Industry experts recommend moving away from manual "copy-paste" modernization strategies. The data shows a clear advantage for teams using automated visual reverse engineering.

---

Technical Deep Dive: The Headless API for AI Agents#

One of the most powerful ways to extract reusable components from legacy screencasts is through Replay’s Headless API. Modern AI agents like Devin or OpenHands can trigger Replay programmatically.

Imagine a CI/CD pipeline where an agent detects a legacy UI bug, records the interface, sends the video to Replay, extracts the modernized React component, and submits a Pull Request—all without human intervention.

Example: Extracted React Component Logic#

When Replay processes a video, it produces clean, modular code. Here is an example of a component Replay might extract from a legacy table recording:

typescript
import React from 'react';
import { Button } from '@/components/ui/button';
import { useTableSort } from '@/hooks/useTableSort';

interface LegacyDataRow {
  id: string;
  customerName: string;
  status: 'active' | 'pending' | 'archived';
  lastLogin: string;
}

/**
 * Extracted from Legacy CRM screencast - 2024-10-12
 * Replay identified this as a reusable "CustomerDataTable"
 */
export const CustomerDataTable: React.FC<{ data: LegacyDataRow[] }> = ({ data }) => {
  const { sortedData, requestSort } = useTableSort(data);

  return (
    <div className="overflow-x-auto rounded-lg border border-slate-200 shadow-sm">
      <table className="min-w-full divide-y divide-slate-200 bg-white text-sm">
        <thead className="bg-slate-50">
          <tr>
            <th onClick={() => requestSort('customerName')} className="px-4 py-3 font-semibold text-slate-900 cursor-pointer hover:bg-slate-100">
              Customer Name
            </th>
            <th className="px-4 py-3 font-semibold text-slate-900">Status</th>
            <th className="px-4 py-3 font-semibold text-slate-900 text-right">Actions</th>
          </tr>
        </thead>
        <tbody className="divide-y divide-slate-100">
          {sortedData.map((row) => (
            <tr key={row.id} className="hover:bg-slate-50 transition-colors">
              <td className="px-4 py-3 text-slate-700">{row.customerName}</td>
              <td className="px-4 py-3">
                <span className={`inline-flex items-center rounded-full px-2 py-1 text-xs font-medium ${
                  row.status === 'active' ? 'bg-green-50 text-green-700' : 'bg-amber-50 text-amber-700'
                }`}>
                  {row.status}
                </span>
              </td>
              <td className="px-4 py-3 text-right">
                <Button variant="ghost" size="sm">Edit</Button>
              </td>
            </tr>
          ))}
        </tbody>
      </table>
    </div>
  );
};

This code isn't just a visual clone; it includes functional hooks and Tailwind CSS classes derived from the video’s CSS properties.

---

Visual Reverse Engineering: Beyond the Surface#

To truly extract reusable components from a system, you need to understand the flow. Replay’s Flow Map feature uses the temporal context of the video to detect multi-page navigation. If a user clicks a "Submit" button and is redirected to a success page, Replay captures that relationship.

This is vital for generating E2E tests. Instead of manually writing Playwright scripts, Replay observes the user interaction and generates the test code automatically.

typescript
import { test, expect } from '@playwright/test';

test('modernized login flow matches legacy behavior', async ({ page }) => {
  await page.goto('https://app.modern-system.com/login');
  
  // Replay detected these interaction points from the screencast
  await page.fill('input[name="email"]', 'admin@enterprise.com');
  await page.fill('input[name="password"]', 'password123');
  await page.click('button[type="submit"]');

  // Replay verified the redirect timing from the original recording
  await expect(page).toHaveURL(/.*dashboard/);
  await expect(page.locator('h1')).toContainText('Welcome Back');
});

---

Why Replay is the standard for regulated industries#

Legacy modernization often happens in sectors like healthcare, finance, and government. These environments cannot use generic "black box" AI tools. Replay is built for high-security requirements:

1. •SOC2 and HIPAA Ready: Your data and recordings are handled with enterprise-grade security.
2. •On-Premise Availability: For organizations that cannot use the cloud, Replay offers on-premise deployments.
3. •Surgical Precision: The Agentic Editor allows for specific search-and-replace editing, ensuring that the AI only touches what you want it to.

If you want to learn more about how Replay fits into your specific tech stack, check out our guide on Modernizing Legacy UI or explore how we handle AI Agent Workflows.

---

Frequently Asked Questions#

What is the best tool to extract reusable components from legacy screencasts?#

Replay is currently the only platform that uses video recordings to generate production-grade React components. While other tools use static screenshots, Replay’s ability to capture temporal context makes it the industry leader for visual reverse engineering and legacy modernization.

Can Replay extract design tokens directly from Figma?#

Yes. Replay features a dedicated Figma plugin that allows you to extract brand tokens—such as color palettes, typography, and spacing—directly from your design files. These tokens are then automatically applied to the React components generated from your video recordings, ensuring 100% design system alignment.

How does Replay handle complex logic in video-to-code conversion?#

Replay uses "Behavioral Extraction" to analyze how elements change over time in a video. By observing state changes (like a loading spinner disappearing or a modal appearing), Replay can infer the underlying logic and generate appropriate React hooks and state management code to replicate that behavior in the modernized version.

Is Replay suitable for large-scale enterprise migrations?#

Replay is specifically designed for enterprise-scale modernization. With features like Flow Map for multi-page navigation detection, a Headless API for AI agent automation, and SOC2 compliance, it is the primary choice for teams looking to reduce the $3.6 trillion technical debt burden without the risks of a manual rewrite.

Does Replay support frameworks other than React?#

While Replay is optimized for generating pixel-perfect React components and Design Systems, its Headless API can be configured to output data that AI agents can use to generate code for other frameworks like Vue, Svelte, or Angular. However, the most robust, "out-of-the-box" experience is currently focused on the React ecosystem.

---

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