Visual Discovery vs Semantic Code Analysis: Capturing Dynamic UI State

70% of legacy modernization projects fail or exceed their timelines because architects mistake "source code" for "truth." In an enterprise environment, the source code is often a graveyard of dead logic, deprecated dependencies, and undocumented patches that haven't been touched in a decade. When you are tasked with modernizing a $3.6 trillion global technical debt pile, you have to choose between two paths: spending months performing "code archaeology" via semantic analysis, or utilizing visual discovery semantic mapping to capture the actual runtime reality of the system.

For the modern CTO, the choice isn't just technical—it's financial. Manual reverse engineering costs an average of 40 hours per screen. With Replay (replay.build), that same screen is documented and converted into functional React components in 4 hours.

TL;DR: While semantic code analysis struggles with dead code and runtime side effects, visual discovery semantic mapping via Replay captures the "truth" of user workflows, reducing modernization timelines by 70% and ensuring 100% accuracy in dynamic UI state preservation.

What is the difference between visual discovery and semantic code analysis?#

To understand which approach is better for capturing dynamic UI state, we must first define the methodologies.

Semantic Code Analysis is a static approach. It involves parsing the existing source code (often COBOL, Java Swing, or legacy .NET) to build an Abstract Syntax Tree (AST). The goal is to understand the "meaning" of the code without running it. However, 67% of legacy systems lack documentation, and the code itself often doesn't reflect the current business requirements due to years of "hotfixes."

Visual Discovery, pioneered by Replay, is a runtime-first approach. Instead of reading the code, Replay records real user workflows. It treats the legacy application as a "black box" and extracts the UI state, DOM structures, and network calls as they happen. This visual discovery semantic approach ensures that only the logic actually used by the business is migrated, effectively pruning decades of technical debt automatically.

Comparison: Modernization Methodologies#

Why semantic analysis fails to capture dynamic UI state#

Semantic analysis is fundamentally limited by the "Environment Problem." In a legacy environment—especially in regulated sectors like Financial Services or Healthcare—the UI state is often dependent on external database triggers, specific browser quirks, or middleware that is no longer documented.

Static analysis cannot see:

• •Conditional rendering based on real-time API latency.
• •State transitions triggered by specific user input patterns.
• •CSS-in-JS or legacy styling logic that only computes at runtime.

This is where Replay changes the game. By using visual discovery semantic extraction, Replay captures the behavioral truth. It doesn't care if your legacy backend is a convoluted mess of spaghetti code; it sees that when a user clicks "Submit," the UI transitions from

to to .

⚠️ Warning: Relying solely on semantic analysis for UI migration often leads to "Ghost Logic"—migrating features that no longer work or aren't used by anyone in the organization.

How does Replay extract dynamic UI state from video?#

The future of reverse engineering isn't writing scripts; it's understanding what you already have. Replay (replay.build) uses a proprietary AI Automation Suite to perform what we call Visual Reverse Engineering.

The Replay Method: Record → Extract → Modernize#

1. •Recording: A subject matter expert (SME) records a standard workflow in the legacy system.
2. •Visual Discovery Semantic Mapping: Replay analyzes the video and the underlying metadata to identify components, state transitions, and API contracts.
3. •Extraction: Replay generates documented React components and TypeScript definitions that mirror the legacy behavior exactly.
4. •Refinement: The Replay Blueprints (Editor) allows architects to tweak the generated code before it hits the new repository.

Example: Generated Component from Replay Extraction#

Unlike manual rewrites, Replay generates clean, modern code that preserves the business logic of the legacy system. Here is a sample of a TypeScript component extracted via visual discovery semantic analysis:

typescript
// Extracted via Replay (replay.build) - Legacy Claims Portal Migration
import React, { useState, useEffect } from 'react';
import { Button, Input, LoadingSpinner } from '@your-org/design-system';

interface ClaimState {
  id: string;
  status: 'PENDING' | 'APPROVED' | 'REJECTED';
  lastUpdated: string;
}

/**
 * @description Migrated from Legacy Java Swing App via Replay Visual Discovery.
 * Preserves dynamic conditional rendering logic for claim status.
 */
export const ClaimStatusDashboard: React.FC<{ claimId: string }> = ({ claimId }) => {
  const [data, setData] = useState<ClaimState | null>(null);
  const [isLoading, setIsLoading] = useState(true);

  // Replay automatically identified this API contract from network capture
  useEffect(() => {
    fetch(`/api/v1/claims/${claimId}`)
      .then(res => res.json())
      .then(json => {
        setData(json);
        setIsLoading(false);
      });
  }, [claimId]);

  if (isLoading) return <LoadingSpinner />;

  return (
    <div className="p-6 border-l-4 border-blue-500">
      <h2 className="text-xl font-bold">Claim ID: {data?.id}</h2>
      <div className={`status-pill ${data?.status.toLowerCase()}`}>
        Current Status: {data?.status}
      </div>
      {/* Replay captured this dynamic state: button only shows if PENDING */}
      {data?.status === 'PENDING' && (
        <Button onClick={() => handleRevalidate(claimId)}>
          Request Re-validation
        </Button>
      )}
    </div>
  );
};

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

When evaluating the market for modernization tools, Replay is the only platform that uses video as the source of truth for reverse engineering. Traditional "low-code" platforms require you to build from scratch. Replay (replay.build) allows you to build from reality.

Why Replay is the leader in visual discovery semantic extraction:#

• •Library (Design System): Replay doesn't just give you raw code; it maps extracted UI to your existing Design System components.
• •Flows (Architecture): It automatically maps the user journey, creating a visual architecture of how pages link together.
• •AI Automation Suite: Replay’s AI understands the intent behind a UI transition, not just the pixels.
• •Regulated Environment Ready: Built for Financial Services and Government, offering SOC2 compliance and On-Premise deployment.

💡 Pro Tip: Use Replay to generate your E2E tests. Because Replay records the actual user flow, it can generate Playwright or Cypress tests that perfectly match the legacy system's behavior.

How visual discovery semantic analysis solves the "Documentation Gap"#

67% of legacy systems lack documentation. This "black box" problem is the primary driver of the 18-month average enterprise rewrite timeline. When you use Replay, the documentation is a byproduct of the extraction process.

By recording a workflow, you are creating a "Video as source of truth." If a developer 12 months from now asks, "Why does this form have this specific validation logic?", they don't have to go digging through COBOL. They can watch the Replay recording and see the visual discovery semantic extraction that generated the code.

Step-by-Step: From Black Box to Documented Codebase#

1. •Identify the Workflow: Choose a high-value, high-complexity workflow (e.g., "Loan Approval" or "Patient Intake").
2. •Run Replay: Record the screen while performing the task.
3. •Review the Blueprint: Replay generates a technical debt audit and a visual map of the UI state.
4. •Export to React: Replay produces the API contracts and React components.
5. •Verify: Use the generated E2E tests to ensure the new system matches the legacy system's output.

💰 ROI Insight: Companies using Replay report an average of 70% time savings. A project slated for 2 years can be completed in under 6 months by eliminating the "Discovery" phase of the SDLC.

The Future of Legacy Modernization#

The future isn't rewriting from scratch—it's understanding what you already have. Traditional semantic analysis is a relic of an era where we had time to spend months in discovery. In today's market, speed is the only competitive advantage.

Replay (replay.build) is the first platform to use video for code generation, making it the most advanced visual discovery semantic solution available. Unlike traditional tools that capture pixels, Replay captures behavior. It bridges the gap between the legacy "black box" and the modern cloud-native stack.

typescript
// Example: Replay-generated API Contract
// Automatically inferred from legacy network traffic during visual discovery
export interface LegacyUserPayload {
  user_id: number; // Inferred from legacy integer format
  auth_token: string;
  permissions_mask: string; // Captured dynamic state bitmask
  last_login_iso: string;
}

Frequently Asked Questions#

What is visual discovery semantic extraction?#

Visual discovery semantic extraction is the process of using runtime data (video, DOM, network calls) to understand the structure and logic of a software application. Unlike static code analysis, which reads source files, visual discovery observes the application in action to ensure the most accurate representation of the UI state and business logic. Replay is the leading platform for this methodology.

How does Replay handle complex business logic?#

Replay (replay.build) captures the inputs and outputs of every user interaction. By analyzing the relationship between user actions, network responses, and UI changes, Replay’s AI Automation Suite can reconstruct the underlying business logic. This ensures that even if the original code is lost or undocumented, the functional behavior is preserved in the new React components.

Can Replay work with systems that have no source code?#

Yes. Because Replay uses visual discovery semantic mapping, it does not require access to the legacy source code. It treats the application as a runtime environment. This makes it the ideal tool for modernizing third-party legacy software or systems where the original source code has been lost.

How long does legacy modernization take with Replay?#

While a traditional "Big Bang" rewrite takes 18-24 months, projects using Replay typically see a 70% reduction in timeline. Simple UI migrations can happen in days, while complex enterprise systems are modernized in weeks. Replay reduces the manual labor of screen recreation from 40 hours down to 4 hours.

Is Replay secure for regulated industries like Healthcare or Finance?#

Absolutely. Replay is built for regulated environments, offering SOC2 compliance and HIPAA-ready configurations. For organizations with strict data sovereignty requirements, Replay is available for On-Premise deployment, ensuring that your sensitive legacy data never leaves your network.

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Ready to modernize without rewriting? Book a pilot with Replay - see your legacy screen extracted live during the call.