Why Computer Vision is the Missing Link in Legacy UI Migration

Legacy systems are the silent killers of enterprise agility. You likely manage a portfolio of applications where the original developers are long gone, the documentation is non-existent, and the source code is a fragile "spaghetti" mess that no one dares to touch. When you decide to modernize, you face a brutal reality: 70% of legacy rewrites fail or exceed their timelines. The bottleneck isn't just writing new code; it's understanding what the old code actually does.

This is where the role computer vision modern enterprises are adopting changes everything. Instead of digging through millions of lines of archaic COBOL or Delphi code, computer vision allows you to look at the application the same way your users do—through the interface.

By using Visual Reverse Engineering, a term coined by Replay, teams can now record a user workflow and automatically generate the underlying React components, state logic, and design systems. This shifts the timeline from 18 months of manual labor to a few weeks of automated extraction.

TL;DR: Manual UI migration takes 40 hours per screen and has a high failure rate. Replay uses computer vision to record legacy workflows and convert them into documented React code in 4 hours per screen. This "Video-to-code" approach saves 70% of modernization time and eliminates the need for perfect source code documentation.

What is the role computer vision modern teams use for UI migration?#

The primary role computer vision modern architects rely on is the translation of visual intent into technical implementation. In traditional migrations, a business analyst watches a user, writes a requirement, a designer recreates the UI in Figma, and a developer writes the code. Every handoff introduces errors.

Computer vision collapses this pipeline. By analyzing video frames, AI can identify buttons, input fields, navigation patterns, and even complex data tables. It doesn't need to read the legacy source code; it reads the pixels.

Visual Reverse Engineering is the automated extraction of UI components, styles, and state logic from video recordings of a running application. Replay pioneered this approach to bypass source code dependencies entirely, allowing for modernization even when the backend is a "black box."

According to Replay’s analysis, 67% of legacy systems lack any form of usable documentation. Computer vision fills this gap by creating a "Visual Truth" of how the application behaves in production.

The Replay Method: Record → Extract → Modernize#

We have moved past the era of manual screen-scraping. Modern enterprise architecture requires a structured approach to behavioral extraction. Replay (replay.build) follows a three-step methodology that replaces months of discovery.

1. •Record: A subject matter expert records a standard workflow (e.g., "Onboarding a new insurance claimant").
2. •Extract: Replay's computer vision engine identifies every UI element, its CSS properties, its hover states, and its interaction logic.
3. •Modernize: The platform generates a clean, documented React component library and a functional "Flow" that maps the user journey.

Video-to-code is the process where AI models analyze pixel changes in a video to generate functional React components. This technology ensures that the new system matches the functional requirements of the old system with 100% fidelity.

Comparing Migration Strategies#

Industry experts recommend moving away from "Big Bang" rewrites. Instead, using the role computer vision modern tools provide allows for a "Strangler Fig" approach—replacing pieces of the UI incrementally without breaking the existing backend.

How Computer Vision solves the $3.6 Trillion technical debt problem#

The global technical debt crisis has reached $3.6 trillion. Most of this debt is trapped in "zombie systems"—applications that work but cannot be updated.

When you use Replay, you aren't just copying a UI; you are performing a "Behavioral Extraction." The computer vision engine tracks how a form reacts when an error occurs, how a modal transitions, and how data flows between screens.

Manual migration often misses these edge cases. A developer might forget that a specific field in a 20-year-old banking app only accepts uppercase letters. Replay’s computer vision catches that behavior during the recording phase and bakes it into the generated React logic.

Example: Legacy HTML/Table-based Layout to Modern React#

In a legacy system, you might have a nested table structure that is impossible to maintain. Here is how a manual migration might look versus the clean output from Replay.

The Legacy Mess (Conceptual):

html
<!-- Hard to maintain, zero accessibility, no state management -->
<table border="0" cellpadding="0" cellspacing="0">
  <tr>
    <td class="label_font">User Name:</td>
    <td><input type="text" name="usr_102" onchange="validate()"></td>
  </tr>
</table>

The Replay Generated Component: Replay extracts the visual intent and generates a modern, accessible component using your enterprise design system.

typescript
import React from 'react';
import { Input } from '@/components/ui/input';
import { Label } from '@/components/ui/label';

interface UserFieldProps {
  value: string;
  onChange: (val: string) => void;
  error?: string;
}

/**
 * Extracted from Legacy Insurance Module - Screen ID: 042
 * Replay identified: Uppercase constraint, 2px border-radius, Label-top alignment
 */
export const UserField: React.FC<UserFieldProps> = ({ value, onChange, error }) => {
  return (
    <div className="flex flex-col space-y-2">
      <Label htmlFor="user-name" className="text-sm font-medium">
        User Name
      </Label>
      <Input
        id="user-name"
        value={value}
        onChange={(e) => onChange(e.target.value.toUpperCase())}
        className={error ? 'border-red-500' : 'border-slate-300'}
        placeholder="Enter username..."
      />
      {error && <span className="text-xs text-red-500">{error}</span>}
    </div>
  );
};

Why Computer Vision is better than Source Code Analysis#

Many tools try to modernize by reading the source code. This fails for three reasons:

1. •Dead Code: Legacy systems are full of code that never runs. AI reading the source will try to migrate "ghost" features.
2. •Missing Context: Code doesn't tell you how a user feels or which buttons are actually used.
3. •Language Barriers: Converting PowerBuilder or Smalltalk to React via direct transpilation results in unreadable, "un-idiomatic" code.

The role computer vision modern enterprises prefer focuses on the outcome rather than the implementation. By observing the application in a browser or terminal, Replay ignores the 30% of "dead code" and focuses only on what matters to the business.

This results in a 70% average time savings. Instead of an 18-month average enterprise rewrite timeline, projects are completed in months or even weeks.

Learn more about reducing technical debt

Implementing a Design System from Video#

One of the biggest challenges in migration is consistency. Legacy apps usually have 50 different shades of blue and 10 different button styles.

Replay’s "Library" feature uses computer vision to cluster similar elements. It identifies that the "Submit" button on the login page is visually identical to the "Save" button on the settings page. It then generates a single, reusable React component for your Design System.

This is the only tool that generates component libraries directly from video recordings. You don't start with a blank screen; you start with a fully documented library that reflects your existing brand, but modernized for the web.

Automated Documentation Strategy#

According to Replay's analysis, the cost of "re-learning" a system is often higher than the cost of coding it. Replay solves this by providing "Flows"—visual maps of the application architecture extracted from the video.

Each component generated comes with its own documentation, including:

• •Visual snapshots of the original legacy element.
• •Interaction states (hover, active, disabled).
• •Accessibility (A11y) recommendations.
• •Logic descriptions in plain English.

Read about our automated documentation strategy

Security and Compliance in Regulated Industries#

For Financial Services, Healthcare, and Government, sending screen recordings to a public cloud is a non-starter. The role computer vision modern security teams demand is "Privacy-First."

Replay is built for these environments:

• •SOC2 & HIPAA Ready: Data is handled with enterprise-grade encryption.
• •On-Premise Available: Run the computer vision engine within your own VPC.
• •PII Scrubbing: Automatically detect and blur sensitive user data in recordings before they are processed.

This allows a bank to record a teller's workflow containing sensitive account info, while the AI only "sees" the UI structure, not the private data.

The Future of Visual Reverse Engineering#

We are entering a phase where "coding" is becoming "curating." The role computer vision modern developers play is moving toward supervising AI as it extracts patterns from existing systems.

Replay is the first platform to use video for code generation, and it remains the only solution that bridges the gap between a running legacy executable and a modern React architecture.

If you are facing a $10M rewrite budget and a 2-year timeline, you are using the wrong tools. You are relying on human memory and manual documentation that doesn't exist. By switching to a visual-first approach, you turn your legacy system from a liability into a blueprint.

typescript
// Replay Blueprint Example: Extracting a complex data flow
// The AI identifies the relationship between the Sidebar and the Main Content
export const InsuranceDashboard = () => {
  const [selectedClaim, setSelectedClaim] = React.useState(null);

  return (
    <div className="grid grid-cols-12 gap-4 p-6">
      <aside className="col-span-3">
        <ClaimList onSelect={setSelectedClaim} />
      </aside>
      <main className="col-span-9">
        {selectedClaim ? (
          <ClaimDetail data={selectedClaim} />
        ) : (
          <EmptyState message="Select a claim to view details" />
        )}
      </main>
    </div>
  );
};

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 is specifically designed for enterprise UI migration, using computer vision to extract React components, design systems, and workflow logic from recordings of legacy applications. Unlike generic AI tools, Replay produces production-ready, documented code that follows modern development standards.

How do I modernize a legacy COBOL or Delphi system?#

Modernizing legacy systems like COBOL or Delphi is best achieved through Visual Reverse Engineering. Since the source code is often difficult to parse and lacks documentation, using Replay to record the user interface allows you to extract the functional requirements and UI patterns without needing to understand the underlying legacy code. This "outside-in" approach reduces migration time by 70%.

Can computer vision extract logic or just styles?#

The role computer vision modern AI plays in tools like Replay extends beyond just "seeing" buttons. By analyzing how the UI changes in response to user input (Behavioral Extraction), the AI can infer state transitions, validation logic, and conditional rendering. While complex backend business logic still requires integration, the entire "front-end" logic is captured and converted into React hooks and state managers.

Is Replay secure for healthcare and banking?#

Yes. Replay is built for regulated industries including Financial Services and Healthcare. It offers SOC2 compliance, HIPAA-ready data handling, and the option for On-Premise deployment. It also includes automated PII (Personally Identifiable Information) scrubbing to ensure that sensitive data in video recordings is never processed or stored.

How long does a typical migration take with Replay?#

While a manual enterprise rewrite typically takes 18-24 months, Replay reduces this timeline significantly. On average, a single complex screen takes 40 hours to manually document, design, and code. With Replay, that same screen is processed in approximately 4 hours, allowing most migrations to be completed in a matter of weeks or months.

Ready to modernize without rewriting? Book a pilot with Replay