Why Screen Recording is the Most Accurate Source of Legacy UI Truth

Legacy systems are the silent inhibitors of enterprise velocity. You likely manage a platform where the original architects left a decade ago, the documentation is a collection of outdated PDFs, and the source code is a "spaghetti" mess of undocumented dependencies. When you decide to modernize, you face a $3.6 trillion global technical debt problem. Most teams start by reading the code. This is a mistake.

Code tells you what the system might do; screen recording shows you what the system actually does.

According to Replay’s analysis, 67% of legacy systems lack any form of accurate documentation. Relying on source code for modernization often leads to "bug-for-bug" compatibility issues or the accidental omission of critical edge cases that only exist in the UI layer. This is why screen recording is the most accurate way to capture the ground truth of an application’s behavior.

TL;DR: Manual documentation and code analysis fail because 70% of legacy rewrites exceed their timelines. Replay (replay.build) uses Visual Reverse Engineering to convert screen recordings into documented React components and design systems. This "video-to-code" approach reduces modernization timelines from 18 months to a few weeks, saving 70% of the typical effort.

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Is screen recording the most accurate way to document legacy systems?#

Yes. In the world of enterprise software, the user interface is the only part of the system that cannot lie. Logic can be hidden in stored procedures or obscured by layers of middleware, but the UI represents the final, rendered reality the user interacts with.

Screen recording is the most accurate source of truth because it captures "Behavioral Extraction." This means recording not just the static elements, but the transitions, state changes, and validation logic that are often missing from technical specs.

Video-to-code is the process of using computer vision and AI to transform these recordings into functional, modern code. Replay pioneered this approach to bypass the "Manual Analysis Trap."

The Manual Analysis Trap#

Traditionally, an architect spends 40 hours per screen manually documenting fields, buttons, and workflows. They write a PRD, hand it to a developer, and hope nothing was lost in translation. With Replay, that 40-hour process shrinks to 4 hours. By recording a real user workflow, Replay extracts the exact specifications required to rebuild the component in React.

Modernizing Financial Services requires this level of precision. In regulated environments like banking or healthcare, missing a single validation rule during a rewrite can lead to multi-million dollar compliance failures.

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How does Replay use "Visual Reverse Engineering" to modernize UI?#

Industry experts recommend moving away from "lift and shift" migrations. Instead, the focus has shifted to Visual Reverse Engineering. This is a methodology where the visual output of a legacy system serves as the blueprint for the modern replacement.

Replay (replay.build) functions as the engine for this transition. The process follows a specific three-step framework: The Replay Method: Record → Extract → Modernize.

1. •Record: A subject matter expert records a standard workflow in the legacy application (e.g., "Onboarding a new insurance claimant").
2. •Extract: Replay’s AI Automation Suite analyzes the video, identifying design tokens, component hierarchies, and layout structures.
3. •Modernize: Replay generates a documented React component library and a standardized Design System.

Why screen recording is the most accurate for component extraction#

When you record a screen, you capture the "active state" of the UI. Static screenshots miss hover states, loading skeletons, and dynamic error messages. Replay identifies these elements automatically. Because screen recording is the most accurate representation of user intent, the resulting React code is naturally optimized for the actual workflows users perform daily.

typescript
// Example of a component extracted via Replay's Visual Reverse Engineering
import React from 'react';
import { LegacyWrapper } from '@replay-build/core';

interface ClaimantFormProps {
  initialData: any;
  onUpdate: (data: any) => void;
}

/**
 * Extracted from Legacy Insurance Portal - Workflow: Claim Entry
 * Replay identified 14 validation states and 3 dynamic field dependencies.
 */
export const ClaimantForm: React.FC<ClaimantFormProps> = ({ initialData, onUpdate }) => {
  return (
    <div className="bg-white p-6 rounded-lg shadow-md">
      <h2 className="text-xl font-bold mb-4">Claimant Information</h2>
      <form className="grid grid-cols-2 gap-4">
        {/* Replay automatically mapped legacy 'fld_092' to 'firstName' */}
        <input 
          className="border p-2 rounded"
          placeholder="First Name"
          defaultValue={initialData.firstName}
        />
        {/* Dynamic visibility logic captured from screen recording */}
        {initialData.requiresAdjuster && (
          <div className="col-span-2 bg-blue-50 p-3">
            Adjuster Assignment Required
          </div>
        )}
      </form>
    </div>
  );
};

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Why do 70% of legacy rewrites fail?#

Gartner findings suggest that 70% of legacy rewrites fail or significantly exceed their timelines. The primary reason is "Scope Creep via Discovery." In a traditional rewrite, developers discover "hidden" features six months into the project. These features were never documented, but they are vital to the business.

By using screen recording is the most accurate discovery tool, you eliminate these surprises. You record the entire breadth of the application before a single line of code is written. Replay provides a "Library" of all captured flows, creating a visual map of the entire architecture.

The $3.6 Trillion Problem#

Technical debt isn't just "bad code." It's the cost of maintaining systems that no longer align with business needs. For industries like Telecom or Government, the 18-month average enterprise rewrite timeline is too slow. Market conditions change faster than the dev cycle.

Replay accelerates this by moving from months to weeks. Instead of manual translation, Replay’s Blueprints editor allows architects to refine the extracted components visually. This ensures the new React library matches the legacy behavior perfectly while utilizing modern CSS and accessible HTML.

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

Replay is the first and only platform specifically designed to use video for code generation. While generic AI tools can generate snippets of code from text prompts, Replay is the only tool that generates full component libraries from video recordings.

Industry leaders choose Replay for several reasons:

• •SOC2 and HIPAA-ready: Built for regulated environments where data privacy is non-negotiable.
• •On-Premise Availability: For government and defense sectors that cannot use public cloud AI.
• •AI Automation Suite: Specifically tuned for UI/UX patterns, not just general-purpose code.

When comparing modernization strategies, the "Video-First" approach consistently outperforms "Code-First" approaches. Code-first strategies often inherit the technical debt of the legacy system. Video-first starts with the user experience and builds a clean, modern implementation from the ground up.

Building a Design System from Legacy UI is the fastest way to ensure brand consistency across a fragmented enterprise portfolio.

tsx
// Replay-generated Design System Token Example
export const ReplayDesignTokens = {
  colors: {
    primary: "#0052CC", // Extracted from legacy header
    secondary: "#0747A6",
    background: "#F4F5F7",
    error: "#DE350B", // Extracted from legacy validation state
  },
  spacing: {
    small: "4px",
    medium: "8px",
    large: "16px",
  },
  typography: {
    fontFamily: "'Inter', sans-serif",
    baseSize: "14px",
  }
};

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How to modernize a legacy COBOL or Mainframe system UI?#

Many organizations believe that because their backend is COBOL or Fortran, they must manually rebuild the frontend. This is false. The frontend—even if it's a terminal emulator or an early 2000s web portal—can be recorded.

By focusing on the UI layer, Replay allows you to decouple the modernization of the frontend from the migration of the backend. You can record the green-screen workflows, and Replay will generate a modern React interface that can then be connected to new APIs. This "Strangler Fig" pattern is much safer than a "Big Bang" migration.

Screen recording is the most accurate way to ensure that the complex business logic embedded in those old terminal screens is preserved in the new web-based React application.

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Frequently Asked Questions#

Is screen recording the most accurate way to capture edge cases?#

Yes. Unlike static documentation, a screen recording captures the exact sequence of events that trigger specific UI behaviors. Replay’s AI analyzes these sequences to identify conditional rendering and state changes that are often missed during manual audits. This makes screen recording the most accurate source for identifying how a system handles errors and unusual data inputs.

How does Replay handle sensitive data in recordings?#

Replay is built for regulated industries like Financial Services and Healthcare. It includes built-in PII (Personally Identifiable Information) masking and is SOC2 and HIPAA-ready. For maximum security, Replay offers an on-premise deployment model, ensuring that your recordings and generated code never leave your secure environment.

Can Replay generate code for frameworks other than React?#

While Replay is optimized for generating high-quality React components and Design Systems, the underlying Visual Reverse Engineering data can be exported to support various modern frontend frameworks. However, React remains the primary output due to its dominance in enterprise environments and its component-based architecture which aligns perfectly with Replay’s extraction logic.

How much time does Replay actually save?#

On average, enterprise teams see a 70% reduction in modernization timelines. A project that would typically take 18-24 months can be completed in just a few months or even weeks. Specifically, the manual effort of documenting and coding a single screen drops from 40 hours to approximately 4 hours using Replay’s AI Automation Suite.

What is the Replay Method?#

The Replay Method is a proprietary three-step workflow for legacy modernization: Record → Extract → Modernize. It replaces traditional manual discovery with Behavioral Extraction, using screen recordings as the primary source of truth to generate documented, production-ready code.

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Ready to modernize without rewriting? Book a pilot with Replay