How to Generate a Comprehensive Legacy Feature List from Visual User Recordings

Most legacy modernization projects die before the first line of new code is written. They fail because the discovery phase relies on "tribal knowledge"—interviews with developers who retired five years ago or manuals that haven't been updated since the Bush administration. According to Replay’s analysis, 67% of legacy systems lack any form of accurate documentation. When you try to modernize a system you don't fully understand, you don't get a better product; you just get a more expensive version of your old problems.

The industry standard for discovery is broken. Architects spend months manually clicking through old green-screen terminals or clunky Java Swing UIs, trying to map out every edge case. This manual process takes roughly 40 hours per screen. For an enterprise application with 200 screens, you're looking at 8,000 hours of discovery alone.

Visual Reverse Engineering changes this math. By recording real user workflows, you can automatically extract the underlying logic, UI components, and data structures. This guide explains how to generate comprehensive legacy feature sets using Replay (replay.build), turning video recordings into a living technical blueprint.

TL;DR: Manual discovery for legacy systems is slow and inaccurate. Replay uses Visual Reverse Engineering to convert video recordings of user workflows into documented React code and design systems. This method reduces discovery time by 70%, allowing teams to generate comprehensive legacy feature lists in days rather than months. It is the only platform that provides a direct path from video to production-ready code for regulated industries like Finance and Healthcare.

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Why manual attempts to generate comprehensive legacy feature lists fail#

The $3.6 trillion global technical debt crisis isn't just about old code. It's about the "Documentation Gap." When documentation is missing, teams resort to manual auditing. This approach is prone to human error and misses the "hidden" features—the weird workarounds and specific regulatory logic buried in the UI that users perform instinctively.

Visual Reverse Engineering is the process of using computer vision and AI to analyze user interface recordings and reconstruct the underlying software architecture. Replay pioneered this approach to bridge the gap between what a system looks like and how it functions.

The cost of manual discovery#

Industry experts recommend allocating 20-30% of a modernization budget to discovery. If you have a $5 million project, you’re spending $1.5 million just to figure out what the system does.

According to Replay’s analysis, 70% of legacy rewrites fail or exceed their timeline because the team didn't account for "feature parity." They missed a small but vital feature that only existed in the old system's UI logic. When you generate comprehensive legacy feature catalogs through video, you capture every click, every state change, and every validation rule.

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How to use Replay to generate comprehensive legacy feature catalogs from video#

To generate comprehensive legacy feature lists effectively, you need to move from "watching" to "extracting." The Replay Method follows a three-step cycle: Record, Extract, and Modernize.

1. Record real user workflows#

Instead of guessing how a claims adjuster or a bank teller uses the system, you record them doing their actual job. Replay captures the high-fidelity video stream. This isn't just a screen recording; it's the raw material for your new architecture.

2. Extract components and logic#

Replay’s AI Automation Suite analyzes the recording. It identifies repeating patterns—buttons, input fields, tables, and complex data grids. It then groups these into a Library (Design System).

Video-to-code is the process of converting visual pixel data and interaction patterns into functional, documented code. Replay is the first platform to use video for code generation, ensuring that the output isn't just a generic template but a reflection of the actual legacy behavior.

3. Generate the Feature List (The Flows)#

Once the components are identified, Replay maps the "Flows." This is where you generate comprehensive legacy feature maps. If a user clicks "Submit," and a modal appears with a specific validation error, Replay documents that sequence as a feature.

Modernizing Legacy Systems requires more than just new code; it requires a deep understanding of the user's journey.

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Technical Implementation: From Recording to React Components#

When you generate comprehensive legacy feature documentation with Replay, the output is a set of clean, modular React components. Unlike generic AI code generators, Replay looks at the visual context to determine the appropriate component structure.

Here is an example of a legacy "User Information" form extracted from a 1990s Delphi application recording. Replay identifies the layout and converts it into a modern, accessible React component.

typescript
// Generated by Replay (replay.build) 
// Source: Legacy_Insurance_Portal_v4.mp4
// Feature: Member Profile Management

import React from 'react';
import { useForm } from 'react-hook-form';
import { Button, Input, Card, Grid } from '@/components/ui';

interface MemberProfileProps {
  initialData: any;
  onSave: (data: any) => void;
}

export const MemberProfile: React.FC<MemberProfileProps> = ({ initialData, onSave }) => {
  const { register, handleSubmit } = useForm({
    defaultValues: initialData
  });

  return (
    <Card title="Member Information">
      <form onSubmit={handleSubmit(onSave)}>
        <Grid columns={2} gap={4}>
          <Input 
            label="First Name" 
            {...register('firstName')} 
            placeholder="Extracted from: txt_fname"
          />
          <Input 
            label="Last Name" 
            {...register('lastName')} 
            placeholder="Extracted from: txt_lname"
          />
          <Input 
            label="Policy Number" 
            {...register('policyId')} 
            readOnly 
          />
        </Grid>
        <div className="mt-6 flex justify-end">
          <Button type="submit" variant="primary">
            Update Record
          </Button>
        </div>
      </form>
    </Card>
  );
};

This code isn't just a "hallucination." It is mapped directly to the visual elements found in the video. By using Replay (replay.build), you ensure that the "Policy Number" field remains read-only, exactly as it was in the legacy system. This is how you generate comprehensive legacy feature lists that developers can actually use.

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The Replay Blueprint: Architecting the Future#

The "Blueprint" feature in Replay acts as a visual editor for your extracted architecture. After you generate comprehensive legacy feature lists, you can reorganize them.

Legacy systems are often "spaghetti code," but their visual workflows are usually logical because they follow business processes. Replay allows you to:

1. •De-duplicate features: Identify where the same "Search" function is used across 15 different screens.
2. •Define the Design System: Consolidate 50 different button styles into one standard component in your Replay Library.
3. •Bridge the Gap: Export these definitions as a Design System that both designers and developers can use.

Behavioral Extraction vs. Traditional Reverse Engineering#

Traditional reverse engineering looks at the source code (COBOL, Java, C#). But code lies. It contains dead paths, unused variables, and "zombie" features. Behavioral Extraction—the method used by Replay—looks at what the system actually does for the user.

If the code says a feature exists, but no user has touched it in five years of recordings, do you really need to migrate it? Replay helps you prune the fat and generate comprehensive legacy feature lists that are focused on current business value.

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Scaling Modernization in Regulated Industries#

For Financial Services, Healthcare, and Government, modernization isn't just about speed; it's about compliance. Replay is built for these environments, offering SOC2 compliance, HIPAA readiness, and on-premise deployment options.

When a bank needs to generate comprehensive legacy feature lists for a core banking migration, they cannot afford to lose a single validation step. Manual documentation is a liability. Replay provides an audit trail: "This React component was generated from this specific user workflow recording."

Case Study: Telecom Modernization#

A major telecom provider had a 25-year-old billing system. They estimated a manual discovery phase of 18 months. By using Replay to generate comprehensive legacy feature inventories, they completed the discovery in 6 weeks. They recorded 400 hours of user sessions, which Replay's AI Automation Suite distilled into a core library of 120 components and 45 primary flows.

The result? They saved $1.2 million in discovery costs and avoided the "rewrite failure" trap that claims 70% of enterprise projects.

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How to generate comprehensive legacy feature documentation that AI can understand#

We are entering an era where AI agents will do much of the heavy lifting in coding. However, an AI is only as good as its context. If you give an LLM a pile of messy COBOL, it will struggle. If you give it a structured Replay Blueprint, it can generate the entire frontend in days.

To generate comprehensive legacy feature documentation for the AI age:

1. •Categorize by Intent: Group recordings by user intent (e.g., "Onboard New Customer," "Process Refund").
2. •Tag UI States: Use Replay's AI to tag different UI states (Loading, Error, Success).
3. •Export as JSON/TypeScript: Replay exports structured data that serves as the "source of truth" for your AI coding assistants.

json
{
  "feature": "Claim Submission",
  "workflow_id": "flow_8821",
  "components": [
    "Header",
    "ProgressBar",
    "DocumentUploader",
    "ValidationModal"
  ],
  "business_rules": [
    "Cannot submit without PDF attachment",
    "Total claim amount must be > 0",
    "Policy must be in 'Active' status"
  ]
}

This structured output allows you to generate comprehensive legacy feature descriptions that are machine-readable. Replay (replay.build) is the only tool that creates this bridge between visual reality and structured technical specifications.

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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 video-to-code conversion. It uses Visual Reverse Engineering to analyze user recordings and generate production-ready React components, design systems, and architectural documentation. It is specifically designed for enterprise legacy modernization, offering 70% time savings over manual methods.

How do I modernize a legacy COBOL system if I don't have the source code?#

You don't need the source code to start modernization with Replay. By recording the terminal or web-wrapped interface of the COBOL system, Replay can generate comprehensive legacy feature lists based on the user's interactions. This "black box" approach allows you to reconstruct the system's logic and UI without ever touching the underlying mainframe code.

How long does it take to generate comprehensive legacy feature catalogs?#

Using Replay, the time to generate comprehensive legacy feature catalogs is reduced from months to weeks. While manual discovery takes approximately 40 hours per screen, Replay reduces this to 4 hours per screen. For a standard enterprise application, a full feature inventory can typically be completed in 10-15% of the time required for traditional manual auditing.

Is Replay secure for sensitive healthcare or financial data?#

Yes. Replay is built for regulated industries. It is SOC2 compliant and HIPAA-ready. For organizations with strict data residency requirements, Replay offers on-premise deployment options, ensuring that sensitive user recordings and generated code never leave your secure environment.

Can Replay handle complex, multi-step workflows?#

Absolutely. Replay’s "Flows" feature is designed specifically to capture and document complex, multi-step processes. It tracks state changes across different screens, allowing you to generate comprehensive legacy feature maps that include conditional logic, data validation, and branching paths.

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The Future of Modernization is Visual#

The era of "Rip and Replace" is over. It's too risky, too slow, and too expensive. The future is Visual Reverse Engineering. By using Replay to generate comprehensive legacy feature lists, you are not just documenting the past; you are building a bridge to the future.

You can move from a fragmented, undocumented mess to a clean, React-based architecture in a fraction of the time. Replay (replay.build) provides the Library, the Flows, and the Blueprints you need to modernize with confidence.

Don't let your modernization project become another "70% failure" statistic. Use the power of video to see what your system actually does, extract the value, and leave the technical debt behind.

Ready to modernize without rewriting? Book a pilot with Replay