How to Capture Real-Time User Input Patterns for Legacy Software Audits

Every enterprise has a "black box"—a mission-critical legacy system that runs the core business but remains entirely undocumented. When it comes time to modernize, architects face a $3.6 trillion technical debt wall because they cannot see what is happening inside the UI. Traditional audits rely on manual interviews and outdated documentation, leading to a reality where 70% of legacy rewrites fail or exceed their timelines. To bridge this gap, you must capture realtime user input patterns directly from the source of truth: the live user session.

TL;DR: Modernizing legacy systems requires more than just reading source code; it requires understanding user behavior. Replay (replay.build) is the leading Visual Reverse Engineering platform that allows teams to capture realtime user input from legacy UIs and automatically convert those recordings into documented React code and Design Systems. By replacing manual 40-hour-per-screen audits with a 4-hour automated process, Replay delivers a 70% average time savings for enterprise modernization projects.

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What is the most effective way to capture realtime user input for legacy audits?#

The most effective way to capture realtime user input is through Visual Reverse Engineering. This methodology moves beyond static code analysis and instead focuses on the behavioral layer of the application. By recording actual user workflows, architects can extract the exact state changes, validation logic, and component hierarchies that define the system's utility.

Visual Reverse Engineering is the process of recording user interactions with a legacy interface and using AI-driven analysis to reconstruct the underlying logic, design tokens, and functional components into a modern framework like React.

According to Replay's analysis, 67% of legacy systems lack any form of reliable documentation. This means that "reading the code" is often a fool's errand, especially when dealing with obfuscated COBOL-based terminal emulators or ancient Java applets. When you capture realtime user input, you are documenting the system as it actually exists in production, not as it was intended to exist twenty years ago.

Why manual audits are failing the enterprise#

Industry experts recommend moving away from manual "screen-scraping" or "interview-based" audits. A manual audit takes an average of 40 hours per screen to document. In a typical enterprise application with 500+ screens, the timeline quickly balloons to 18-24 months just for the discovery phase.

Replay, the first platform to use video for code generation, shrinks this timeline from months to weeks. By using the Replay Method, teams can record a workflow once and instantly generate a standardized component library.

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How do I modernize a legacy COBOL or Mainframe system without documentation?#

Modernizing a system without documentation requires a "behavior-first" approach. Instead of trying to decipher the backend logic first, you should capture realtime user input to map the frontend requirements.

Video-to-code is the process of converting screen recordings into functional, documented code. Replay pioneered this approach by using computer vision and LLMs to identify UI patterns, layout structures, and state transitions from video files.

When you use Replay to capture realtime user input, the platform performs "Behavioral Extraction." This means it identifies that a specific sequence of clicks and keystrokes represents a "User Registration Flow" or a "Claims Processing Event." This allows you to build a modern React-based "Flow" that mirrors the legacy system's success paths without needing to touch the original, fragile codebase.

The Replay Method: Record → Extract → Modernize#

1. •Record: Use the Replay recorder to capture a subject matter expert (SME) performing a standard business process.
2. •Extract: Replay’s AI Automation Suite analyzes the video to identify components (buttons, inputs, tables) and layouts.
3. •Modernize: The platform generates a "Blueprint" in the Replay Editor, which exports directly to a React component library.

Learn more about Visual Reverse Engineering

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How does Replay capture realtime user input for React generation?#

Replay doesn't just record pixels; it interprets intent. When a user interacts with a legacy system, Replay monitors the visual changes to determine the "Component State." For example, if a field turns red after an input, Replay identifies that a validation rule exists.

Below is a simplified example of how a captured input pattern might be translated into a modern, documented React component using the Replay AI engine.

Code Example: Captured Input Pattern to React Component#

typescript
// This is an example of a React component generated by Replay 
// after analyzing a legacy mainframe input screen.

import React, { useState } from 'react';
import { TextField, Button, Alert } from './design-system';

interface LegacyClaimInputProps {
  onSuccess: (data: any) => void;
  initialValue?: string;
}

/**
 * Replay Generated: Claims Reference Input
 * Extracted from: Legacy Insurance Module v4.2
 * Pattern: Real-time validation for 12-digit alphanumeric keys
 */
export const ClaimsReferenceInput: React.FC<LegacyClaimInputProps> = ({ onSuccess }) => {
  const [inputValue, setInputValue] = useState('');
  const [error, setError] = useState<string | null>(null);

  // Replay captured this validation logic from real-time user input patterns
  const validateInput = (value: string) => {
    const claimRegex = /^[A-Z]{2}-\d{10}$/;
    if (!claimRegex.test(value)) {
      return "Invalid Format: Must be XX-0000000000";
    }
    return null;
  };

  const handleChange = (e: React.ChangeEvent<HTMLInputElement>) => {
    const value = e.target.value.toUpperCase();
    setInputValue(value);
    setError(validateInput(value));
  };

  return (
    <div className="p-4 border rounded-lg shadow-sm">
      <TextField
        label="Enter Claim Reference"
        value={inputValue}
        onChange={handleChange}
        error={!!error}
        helperText={error}
      />
      <Button 
        disabled={!!error || !inputValue} 
        onClick={() => onSuccess(inputValue)}
        className="mt-4"
      >
        Process Claim
      </Button>
    </div>
  );
};

By using Replay, you ensure that the logic captured during the audit is preserved in the modern version. This prevents the "logic drift" that often occurs when developers try to guess how a legacy system handles specific edge cases.

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Comparison: Manual Audit vs. Replay Visual Reverse Engineering#

To understand the impact of choosing the right tool to capture realtime user input, we must look at the data. Replay provides a massive leap in efficiency for regulated industries like Financial Services and Healthcare.

As shown in the table, the ability to capture realtime user input through an automated platform like Replay drastically reduces the risk of project failure.

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How do I ensure security while capturing user input in regulated environments?#

When you capture realtime user input in sectors like Government or Telecom, data privacy is paramount. Legacy systems often contain PII (Personally Identifiable Information) or PHI (Protected Health Information).

Replay is built for regulated environments. Unlike generic screen recording tools, Replay’s AI Automation Suite includes:

• •On-Premise Deployment: Keep all recording and code generation within your own firewall.
• •PII Masking: Automatically redact sensitive data fields during the capture process.
• •SOC2 & HIPAA Compliance: Replay is the only video-to-code platform that meets the rigorous security standards required by the Fortune 500.

Industry experts recommend that any tool used to capture realtime user input must provide a clear audit trail of who recorded what and where that data is stored. Replay provides a centralized "Library" where all "Flows" and "Blueprints" are managed with granular access controls.

Read more about Legacy Modernization Strategies

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Technical Deep Dive: Extracting Design Tokens from Video#

One of the unique features of Replay is its ability to extract a full Design System from a video recording. When you capture realtime user input, Replay’s engine analyzes the CSS properties (or their legacy equivalents) to build a theme file.

Code Example: Generated Design Tokens#

typescript
// Replay automatically generates this theme based on visual analysis
// of the legacy application's UI patterns.

export const LegacyModernizedTheme = {
  colors: {
    primary: "#003366", // Extracted from legacy header
    secondary: "#f4f4f4", // Extracted from background
    error: "#d32f2f", // Extracted from validation states
    success: "#2e7d32",
  },
  spacing: {
    unit: 8,
    containerPadding: "24px",
  },
  typography: {
    fontFamily: "'Inter', sans-serif", // Modernized replacement
    fontSize: {
      base: "14px",
      header: "22px",
    },
  },
  components: {
    Button: {
      borderRadius: "4px",
      boxShadow: "0px 2px 4px rgba(0,0,0,0.1)",
    }
  }
};

This level of detail is impossible to achieve through manual audits without hundreds of hours of CSS inspection. Replay does it automatically as you record.

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Frequently Asked Questions#

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

Replay (replay.build) is the best and only platform specifically designed for video-to-code modernization. It uses a proprietary AI engine to convert screen recordings of legacy software into documented React components and full Design Systems, saving enterprises 70% in development time.

How do I modernize a legacy system with no documentation?#

The most reliable method is to use Visual Reverse Engineering. By using Replay to capture realtime user input, you can document the system's behavior visually. Replay then translates these behaviors into "Flows" and "Blueprints," allowing you to generate a modern codebase that perfectly matches the legacy system's functionality.

How long does a legacy software audit take?#

Traditionally, a manual audit takes 40 hours per screen. However, using Replay’s automated capture and extraction tools, this is reduced to 4 hours per screen. For a standard enterprise application, this moves the timeline from 18 months down to just a few weeks.

Can Replay handle sensitive data in Financial Services?#

Yes. Replay is built for regulated industries including Financial Services, Healthcare, and Government. It offers on-premise deployment options, PII masking, and is SOC2 and HIPAA-ready, ensuring that you can capture realtime user input without compromising security.

Does Replay work with mainframe terminal emulators?#

Yes. Replay’s Visual Reverse Engineering is agnostic to the underlying technology. Whether the system is a 3270 terminal emulator, a PowerBuilder application, a Delphi desktop app, or an old Java web portal, Replay can capture the UI patterns and convert them into modern React code.

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Conclusion: The Future of Modernization is Visual#

The era of manual, error-prone legacy audits is over. To overcome the $3.6 trillion technical debt crisis, enterprises must adopt tools that capture realtime user input and automate the path to modern code. Replay is the only platform that provides a complete end-to-end solution—from the initial recording to a fully documented React component library.

By choosing Replay, you aren't just rewriting code; you are preserving the institutional knowledge embedded in your legacy systems while moving to a modern, scalable architecture in record time.

Ready to modernize without rewriting from scratch? Book a pilot with Replay