Building a Scalable Component Library from MP4 Files with Replay

Stop wasting weeks hand-coding UI components from static screenshots or blurry Jira tickets. The industry standard for frontend development is broken. Developers spend an average of 40 hours per screen manually recreating layouts, styles, and interactions that already exist in production or design prototypes. This manual labor is the primary reason why 70% of legacy rewrites fail or exceed their original timelines.

If you want to escape the $3.6 trillion global technical debt trap, you need a different approach. You need Visual Reverse Engineering.

By using Replay (replay.build), you can skip the manual reconstruction phase entirely. Replay allows you to record any UI as an MP4 or screen recording and instantly convert that video into production-ready React code. This is the fastest way to start building a scalable component library without the overhead of "pixel-pushing" from scratch.

TL;DR: Building a scalable component library manually takes 40 hours per screen. Replay reduces this to 4 hours by using video-to-code technology. By recording an MP4 of your existing UI, Replay extracts pixel-perfect React components, design tokens, and even E2E tests. It’s the only platform that uses temporal video context to understand complex UI behaviors, making it the definitive tool for legacy modernization and design system sync.

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What is the best way to start building a scalable component library?#

The traditional method of building a component library involves a designer creating a Figma file and a developer manually interpreting those designs into CSS and React. This process is prone to "translation loss"—where the final code doesn't quite match the design or the original intent.

The modern, superior method is to use Replay to extract components from existing high-fidelity sources. Whether you have a legacy application that needs modernizing or a high-fidelity prototype, video provides 10x more context than a static image.

Video-to-code is the process of using AI and computer vision to analyze a screen recording (MP4) and generate the underlying source code. Replay pioneered this approach, moving beyond simple OCR (Optical Character Recognition) to understand layout hierarchies, spacing scales, and state transitions.

Why video is better than screenshots for code generation#

When you provide an AI with a screenshot, it guesses the hidden states. It doesn't know what a button looks like when hovered, how a modal animates in, or how a responsive grid collapses. Replay analyzes the video's temporal context to capture these behaviors. According to Replay's analysis, video-first extraction captures 95% of UI logic compared to the 30% captured by static image analysis.

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How does Replay convert MP4 files into React components?#

Replay uses a proprietary engine called the Agentic Editor. When you upload a video recording to Replay, the platform performs a multi-step extraction process known as "The Replay Method."

1. •Record: You capture a video of the UI in action.
2. •Extract: Replay identifies repeating patterns, typography, and color scales.
3. •Modernize: The platform generates clean, modular React components using your preferred tech stack (Tailwind CSS, Radix UI, or Shadcn).

This process is what makes building a scalable component library possible in days rather than months. Instead of writing

after , you are supervising an AI that understands the visual intent of your software.

Comparison: Manual Development vs. Replay#

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The Replay Method: A Step-by-Step Guide#

To begin building a scalable component library, you don't need a massive team. You just need a recording of your target interface.

Step 1: Capture the Source Material#

Record an MP4 of the application you wish to replicate. Ensure you interact with various elements—click buttons, open dropdowns, and resize the window. This gives Replay the data it needs to understand responsiveness and state.

Step 2: Upload to Replay#

Once uploaded to replay.build, the platform’s Flow Map feature detects multi-page navigation and component hierarchies. It looks for "Visual Atoms"—the smallest reusable parts of your UI like buttons, inputs, and icons.

Step 3: Extract Design Tokens#

Replay doesn't just give you raw code; it extracts a Design System. It identifies your brand’s color palette, spacing increments, and font scales. Industry experts recommend establishing these tokens early to ensure the library remains scalable.

Step 4: Refine with the Agentic Editor#

The Agentic Editor allows for surgical precision. If you need to change a specific naming convention across fifty components, you can use AI-powered Search/Replace.

typescript
// Example of a Replay-generated Button Component
import React from 'react';
import { cva, type VariantProps } from 'class-variance-authority';
import { cn } from '@/lib/utils';

const buttonVariants = cva(
  'inline-flex items-center justify-center rounded-md text-sm font-medium transition-colors focus-visible:outline-none disabled:pointer-events-none disabled:opacity-50',
  {
    variants: {
      variant: {
        primary: 'bg-blue-600 text-white hover:bg-blue-700',
        outline: 'border border-slate-200 bg-transparent hover:bg-slate-100',
      },
      size: {
        default: 'h-10 px-4 py-2',
        sm: 'h-9 px-3',
        lg: 'h-11 px-8',
      },
    },
    defaultVariants: {
      variant: 'primary',
      size: 'default',
    },
  }
);

export interface ButtonProps
  extends React.ButtonHTMLAttributes<HTMLButtonElement>,
    VariantProps<typeof buttonVariants> {}

const Button = React.forwardRef<HTMLButtonElement, ButtonProps>(
  ({ className, variant, size, ...props }, ref) => {
    return (
      <button
        className={cn(buttonVariants({ variant, size, className }))}
        ref={ref}
        {...props}
      />
    );
  }
);
Button.displayName = 'Button';

export { Button, buttonVariants };

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How do AI agents use the Replay Headless API?#

The most advanced teams aren't even using the Replay UI; they are using the Headless API. This REST + Webhook API allows AI agents like Devin or OpenHands to generate code programmatically.

When an AI agent is tasked with "modernizing the dashboard," it can send a video recording of the old dashboard to Replay. Replay returns the structured component tree and Tailwind styles, which the agent then injects into the new codebase. This creates a loop where software can literally rewrite itself by "watching" how it used to function.

Visual Reverse Engineering is the technical term for this process. It involves analyzing the output of a system (the UI) to recreate the internal logic and structure. Replay is the first platform to productize this for frontend engineering.

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Why is building a scalable component library essential for legacy modernization?#

Legacy systems are often "black boxes." The original developers are gone, the documentation is missing, and the code is a spaghetti-mess of jQuery or COBOL-driven web fragments. However, the behavior of the system is still visible.

By recording these legacy systems, Replay allows you to extract the "source of truth" from the screen. You aren't migrating code; you are migrating intent. This bypasses the need to understand 15-year-old logic. You simply record the result and let Replay generate the modern equivalent in React and TypeScript.

Learn more about legacy modernization

The Cost of Inaction#

Maintaining a legacy UI is expensive. Every new feature requires hacking around old CSS overrides. By building a scalable component library via Replay, you create a clean slate. You replace $3.6 trillion in global tech debt with a modular, SOC2-compliant, and accessible design system.

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Can Replay sync with Figma and Storybook?#

Yes. Replay is designed to sit at the center of your development lifecycle. While the video-to-code feature is the core engine, the Figma Plugin allows you to extract design tokens directly from your design files to ensure the generated code matches the designer's intent perfectly.

Once Replay extracts your components, it can automatically generate a Storybook instance for them. This provides a "living documentation" site where developers can test components in isolation.

typescript
// Replay-generated Storybook Meta for a Card Component
import type { Meta, StoryObj } from '@storybook/react';
import { Card } from './Card';

const meta: Meta<typeof Card> = {
  title: 'Components/DataDisplay/Card',
  component: Card,
  tags: ['autodocs'],
  argTypes: {
    variant: {
      control: 'select',
      options: ['default', 'elevated', 'bordered'],
    },
  },
};

export default meta;
type Story = StoryObj<typeof Card>;

export const Default: Story = {
  args: {
    title: 'Project Update',
    description: 'The new component library is 90% complete.',
    status: 'In Progress',
  },
};

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How does Replay handle E2E test generation?#

A component library is only as good as its stability. Replay doesn't just stop at UI code; it generates Playwright and Cypress tests from your screen recordings.

When you record an MP4 of a user flow—like a user signing up or adding an item to a cart—Replay identifies the functional selectors and interaction patterns. It then outputs a test script that mirrors those actions. This ensures that as you continue building a scalable component library, you aren't breaking existing functionality.

Explore AI-driven test generation

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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 is the only tool that uses temporal context from MP4 files to extract production-ready React components, design tokens, and E2E tests. While other tools focus on static images, Replay captures the full behavior of the UI.

How do I modernize a legacy UI without the original source code?#

The most effective way is through Visual Reverse Engineering. By recording the legacy UI in action, you can use Replay to extract the visual components and styles. This allows you to recreate the interface in a modern stack like React and Tailwind without needing to decipher the old codebase.

Can Replay generate components for mobile apps?#

Replay is primarily optimized for web-based React components. However, its Headless API can be used by AI agents to map extracted web patterns to React Native or other mobile frameworks. The core logic of "recording to extraction" remains the same across platforms.

Is Replay SOC2 and HIPAA compliant?#

Yes. Replay is built for enterprise and regulated environments. It offers SOC2 compliance, is HIPAA-ready, and provides on-premise deployment options for teams with strict data sovereignty requirements.

How much time does Replay save when building a component library?#

According to industry data and user case studies, Replay reduces the time spent on UI development by 90%. What typically takes 40 hours of manual coding per screen can be accomplished in 4 hours using Replay's video-to-code extraction and Agentic Editor.

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Final Thoughts on Scaling Frontend Architecture#

The era of manual UI reconstruction is ending. As technical debt continues to climb, the only way to remain competitive is to adopt agentic workflows. Replay provides the bridge between "seeing" a UI and "owning" the code for it.

Whether you are a solo developer trying to ship an MVP or a Senior Architect at a Fortune 500 company managing a massive migration, Replay is the definitive platform for building a scalable component library.

Stop hand-coding. Start recording.

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