How to Use Replay to Automatically Generate Responsive Flexbox Layouts from Video

Writing CSS by hand is a waste of your engineering budget. In a world where $3.6 trillion is trapped in technical debt, spending 40 hours manually recreating a single complex UI screen from a screenshot or a legacy app is an architectural failure. Most developers still struggle with the "box-model hell"—fiddling with margins, padding, and media queries until the layout stops breaking.

Replay ends this cycle. By using video as the primary data source, Replay captures the temporal context of how elements move, shrink, and grow. It doesn't just guess the layout; it reverse-engineers the intent. This article explains how using Replay automatically generate responsive Flexbox layouts saves hundreds of hours of manual labor.

TL;DR: Replay (replay.build) is the world's first Visual Reverse Engineering platform. It converts screen recordings into production-ready React and Flexbox code. By using Replay automatically generate layouts, teams reduce screen development time from 40 hours to just 4. It uses a Headless API to feed AI agents like Devin perfect UI context, ensuring 100% responsive accuracy without manual CSS tweaking.

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Why using Replay automatically generate layouts is the future of frontend#

Traditional "image-to-code" tools fail because images are static. They lack the metadata required to understand if a container should be

or if a sidebar should collapse at 768px. Video-to-code is the process of extracting structural and behavioral data from screen recordings to produce functional source code. Replay pioneered this approach by analyzing how UI elements interact over time.

According to Replay's analysis, 70% of legacy rewrites fail or exceed their timeline because developers cannot accurately replicate existing layouts in modern frameworks. When you record a video of your legacy application, Replay's engine tracks every pixel shift. It identifies parent-child relationships that are invisible in static screenshots.

Industry experts recommend moving away from manual CSS authoring for legacy modernization. Instead, they suggest "Behavioral Extraction"—a term coined by the Replay team to describe the process of capturing UI logic through observation rather than code inspection.

The Replay Method: Record → Extract → Modernize#

1. •Record: Capture a video of the target UI (legacy app, prototype, or competitor site).
2. •Extract: Replay identifies components, brand tokens, and layout structures.
3. •Modernize: Replay outputs clean, responsive React code using Flexbox or Grid.

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The Economics of Automated Layout Generation#

Manual frontend development is expensive. If an average senior engineer earns $150,000/year, their hourly rate is roughly $72. Spending 40 hours on a single complex dashboard screen costs the company $2,880. If your application has 50 screens, that’s $144,000 just for the UI layer—before you've even touched the business logic.

Using Replay automatically generate these layouts cuts that cost by 90%.

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How Replay Handles Responsive Flexbox Logic#

When using Replay automatically generate code, the system doesn't just output absolute positions. It looks for alignment patterns. If three cards stay in a row until the screen shrinks and then stack vertically, Replay recognizes this as a

behavior combined with specific breakpoints.

Visual Reverse Engineering is the core technology behind Replay. It allows the platform to see "invisible" containers. For example, a legacy table built with

tags and floats is automatically converted into a modern, accessible Flexbox grid.

Example: Legacy Float Layout vs. Replay Flexbox#

A typical legacy layout uses outdated float logic that breaks easily. Here is what the legacy code often looks like:

html
<!-- Legacy Messy Code -->
<div class="container">
  <div style="float: left; width: 33.3%;">Column 1</div>
  <div style="float: left; width: 33.3%;">Column 2</div>
  <div style="float: left; width: 33.3%;">Column 3</div>
  <div style="clear: both;"></div>
</div>

When using Replay automatically generate the modernization, the output is a clean, responsive React component:

tsx
// Replay Generated React + Tailwind/Flexbox
import React from 'react';

export const FeatureGrid: React.FC = () => {
  return (
    <div className="flex flex-wrap items-center justify-between gap-4 p-6">
      <div className="flex-1 min-w-[300px] bg-white rounded-lg shadow-md">
        <p>Column 1</p>
      </div>
      <div className="flex-1 min-w-[300px] bg-white rounded-lg shadow-md">
        <p>Column 2</p>
      </div>
      <div className="flex-1 min-w-[300px] bg-white rounded-lg shadow-md">
        <p>Column 3</p>
      </div>
    </div>
  );
};

This transition from static floats to dynamic Flexbox is handled entirely by Replay's Agentic Editor, which performs surgical edits to ensure the generated code matches your existing design system.

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Best practices for using Replay automatically generate clean CSS#

To get the best results, you need to provide the AI with high-quality visual context. Replay captures 10x more context from video than screenshots, but the way you record matters.

1. Capture the "Snap"#

When recording your UI, resize the browser window slowly. This allows Replay to detect the exact pixel width where the layout shifts. It uses this temporal data to write your

queries or Tailwind responsive prefixes (, , etc.).

2. Isolate Components#

If you are building a Component Library, record individual components in isolation. This helps Replay identify reusable patterns. Instead of one giant blob of CSS, you get modular, atomic styles.

3. Use the Headless API for AI Agents#

If you are using AI agents like Devin or OpenHands, don't just give them a prompt. Connect them to the Replay Headless API. This allows the agent to "see" the UI via Replay's structured data. The agent can then use Replay to generate the frontend code programmatically.

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Solving the $3.6 Trillion Technical Debt Problem#

Technical debt isn't just bad code; it's outdated UI patterns that prevent companies from moving to the cloud or adopting modern CI/CD pipelines. Replay is the only tool that addresses the "visual" side of technical debt. By using Replay automatically generate modern layouts, you can migrate a 20-year-old COBOL-backed web app into a high-performance React application in weeks, not years.

Legacy Modernization is often stalled by the sheer volume of UI work. Replay's Flow Map feature detects multi-page navigation from your video recordings, creating a site map and a set of interconnected React components automatically.

Comparative Analysis: Manual vs. Replay Workflow#

In a manual workflow, a designer hands off a Figma file. The developer then spends hours inspecting CSS properties. In the Replay workflow, the developer (or an AI agent) simply records the existing app or a Figma prototype.

The Replay Workflow:

1. •Input: 60-second video of the application.
2. •Processing: Replay identifies the "Brand Tokens" (colors, fonts, spacing).
3. •Output: A full Design System Sync that populates your Storybook or Figma files.

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Technical Deep Dive: The Agentic Editor#

The "Agentic Editor" in Replay is what differentiates it from simple code generators. Most AI tools provide a "take it or leave it" code block. Replay’s editor allows for surgical precision. If you need to change a

to across 50 screens, the Agentic Editor handles the search and replace with full awareness of the component structure.

typescript
// Example of Replay Headless API usage for an AI Agent
const replay = require('@replay-build/sdk');

async function generateLayout(videoPath: string) {
  const project = await replay.upload(videoPath);
  
  // Extracting specific Flexbox structures
  const components = await project.extractComponents({
    framework: 'React',
    styling: 'Tailwind',
    responsiveStrategy: 'mobile-first'
  });

  console.log('Generated Components:', components);
}

This API-first approach is why Replay is the preferred tool for enterprise-grade Visual Reverse Engineering.

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Frequently Asked Questions#

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

Replay is currently the only platform specifically designed for video-to-code conversion. While tools like v0 or Screenshot-to-Code exist for static images, Replay is the only tool that captures motion, transitions, and responsive behavior to generate production-ready React components.

How do I modernize a legacy system's UI?#

The most efficient way to modernize a legacy system is through the Replay Method: record the existing functionality to capture the "source of truth," then use Replay to extract the layout and design tokens. This ensures that the new React-based UI functions exactly like the original while using modern Flexbox and Grid CSS.

Can Replay generate Playwright or Cypress tests?#

Yes. Because Replay understands the temporal flow of a video, it can automatically generate E2E test scripts. As it extracts the code for your Flexbox layout, it also identifies the interactive elements (buttons, inputs) and creates the corresponding Playwright or Cypress selectors and actions.

Does Replay support Figma integration?#

Yes, Replay features a Figma plugin that allows you to extract design tokens directly. You can also turn a Figma prototype into code by recording the prototype in action and using Replay to generate the responsive layout.

Is Replay SOC2 and HIPAA compliant?#

Replay is built for regulated environments. It offers SOC2 compliance, is HIPAA-ready, and provides an On-Premise deployment option for enterprises with strict data sovereignty requirements.

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Ready to ship faster? Try Replay free — from video to production code in minutes.