ui-demo

name	ui-demo
description	Record polished UI demo videos using Playwright. Use when the user asks to create a demo, walkthrough, screen recording, or tutorial video of a web application. Produces WebM videos with visible cursor, natural pacing, and professional feel.
origin	MCC

UI Demo Video Recorder

Record polished demo videos of web applications using Playwright's video recording with an injected cursor overlay, natural pacing, and storytelling flow.

When to Use

• User asks for a "demo video", "screen recording", "walkthrough", or "tutorial"
• User wants to showcase a feature or workflow visually
• User needs a video for documentation, onboarding, or stakeholder presentation

Three-Phase Process

Every demo goes through three phases: Discover -> Rehearse -> Record. Never skip straight to recording.

---

Phase 1: Discover

Before writing any script, explore the target pages to understand what is actually there.

Why

You cannot script what you have not seen. Fields may be <input> not <textarea>, dropdowns may be custom components not <select>, and comment boxes may support @mentions or #tags. Assumptions break recordings silently.

How

Navigate to each page in the flow and dump its interactive elements:

// Run this for each page in the flow BEFORE writing the demo script
const fields = await page.evaluate(() => {
  const els = [];
  document.querySelectorAll('input, select, textarea, button, [contenteditable]').forEach(el => {
    if (el.offsetParent !== null) {
      els.push({
        tag: el.tagName,
        type: el.type || '',
        name: el.name || '',
        placeholder: el.placeholder || '',
        text: el.textContent?.trim().substring(0, 40) || '',
        contentEditable: el.contentEditable === 'true',
        role: el.getAttribute('role') || '',
      });
    }
  });
  return els;
});
console.log(JSON.stringify(fields, null, 2));

What to look for

• Form fields: Are they <select>, <input>, custom dropdowns, or comboboxes?
• Select options: Dump option values AND text. Placeholders often have value="0" or value="" which looks non-empty. Use Array.from(el.options).map(o => ({ value: o.value, text: o.text })). Skip options where text includes "Select" or value is "0".
• Rich text: Does the comment box support @mentions, #tags, markdown, or emoji? Check placeholder text.
• Required fields: Which fields block form submission? Check required, * in labels, and try submitting empty to see validation errors.
• Dynamic content: Do fields appear after other fields are filled?
• Button labels: Exact text such as "Submit", "Submit Request", or "Send".
• Table column headers: For table-driven modals, map each input[type="number"] to its column header instead of assuming all numeric inputs mean the same thing.

Output

A field map for each page, used to write correct selectors in the script. Example:

/purchase-requests/new:
  - Budget Code: <select> (first select on page, 4 options)
  - Desired Delivery: <input type="date">
  - Context: <textarea> (not input)
  - BOM table: inline-editable cells with span.cursor-pointer -> input pattern
  - Submit: <button> text="Submit"

/purchase-requests/N (detail):
  - Comment: <input placeholder="Type a message..."> supports @user and #PR tags
  - Send: <button> text="Send" (disabled until input has content)

---

Phase 2: Rehearse

Run through all steps without recording. Verify every selector resolves.

Why

Silent selector failures are the main reason demo recordings break. Rehearsal catches them before you waste a recording.

How

Use ensureVisible, a wrapper that logs and fails loudly:

async function ensureVisible(page, locator, label) {
  const el = typeof locator === 'string' ? page.locator(locator).first() : locator;
  const visible = await el.isVisible().catch(() => false);
  if (!visible) {
    const msg = `REHEARSAL FAIL: "${label}" not found - selector: ${typeof locator === 'string' ? locator : '(locator object)'}`;
    console.error(msg);
    const found = await page.evaluate(() => {
      return Array.from(document.querySelectorAll('button, input, select, textarea, a'))
        .filter(el => el.offsetParent !== null)
        .map(el => `${el.tagName}[${el.type || ''}] "${el.textContent?.trim().substring(0, 30)}"`)
        .join();
    });
    .( + found);
     ;
  }
  .();
   ;
}

Rehearsal script structure

const steps = [
  { label: 'Login email field', selector: '#email' },
  { label: 'Login submit', selector: 'button[type="submit"]' },
  { label: 'New Request button', selector: 'button:has-text("New Request")' },
  { label: 'Budget Code select', selector: 'select' },
  { label: 'Delivery date', selector: 'input[type="date"]:visible' },
  { label: 'Description field', selector: 'textarea:visible' },
  { label: 'Add Item button', selector: 'button:has-text("Add Item")' },
  { label: 'Submit button', selector: 'button:has-text("Submit")' },
];

let allOk = true;
for (const step of steps) {
  if (!await ensureVisible(page, step.selector, step.label)) {
    allOk = false;
  }
}
if (!allOk) {
  console.error('REHEARSAL FAILED - fix selectors before recording');
  process.exit(1);
}
.();

When rehearsal fails

1. Read the visible-element dump.
2. Find the correct selector.
3. Update the script.
4. Re-run rehearsal.
5. Only proceed when every selector passes.

---

Phase 3: Record

Only after discovery and rehearsal pass should you create the recording.

Recording Principles

1. Storytelling Flow

Plan the video as a story. Follow user-specified order, or use this default:

• Entry: Login or navigate to the starting point
• Context: Pan the surroundings so viewers orient themselves
• Action: Perform the main workflow steps
• Variation: Show a secondary feature such as settings, theme, or localization
• Result: Show the outcome, confirmation, or new state

2. Pacing

• After login: 4s
• After navigation: 3s
• After clicking a button: 2s
• Between major steps: 1.5-2s
• After the final action: 3s
• Typing delay: 25-40ms per character

3. Cursor Overlay

Inject an SVG arrow cursor that follows mouse movements:

async function injectCursor(page) {
  await page.evaluate(() => {
    if (document.getElementById('demo-cursor')) return;
    const cursor = document.createElement('div');
    cursor.id = 'demo-cursor';
    cursor.innerHTML = `<svg width="24" height="24" viewBox="0 0 24 24" fill="none" xmlns="http://www.w3.org/2000/svg">
      <path d="M5 3L19 12L12 13L9 20L5 3Z" fill="white" stroke="black" stroke-width="1.5" stroke-linejoin="round"/>
    </svg>`;
    cursor.style.cssText = `
      position: fixed; z-index: 999999; pointer-events: none;
      width: 24px; height: 24px;
      transition: left 0.1s, top 0.1s;
      filter: drop-shadow(1px 1px 2px rgba(0,0,0,0.3));
    `;
    cursor.style.left = '0px';
    cursor.style.top = '0px';
    document.body.appendChild(cursor);
    document.addEventListener('mousemove', (e) => {
      cursor.style.left = e.clientX + 'px';
      cursor.style.top = e.clientY + 'px';
    });
  });
}

Call injectCursor(page) after every page navigation because the overlay is destroyed on navigate.

4. Mouse Movement

Never teleport the cursor. Move to the target before clicking:

async function moveAndClick(page, locator, label, opts = {}) {
  const { postClickDelay = 800, ...clickOpts } = opts;
  const el = typeof locator === 'string' ? page.locator(locator).first() : locator;
  const visible = await el.isVisible().catch(() => false);
  if (!visible) {
    console.error(`WARNING: moveAndClick skipped - "${label}" not visible`);
    return false;
  }
  try {
    await el.scrollIntoViewIfNeeded();
    await page.waitForTimeout(300);
    const box = await el.boundingBox();
    if (box) {
      await page.mouse.move(box.x + box.width / 2, box.y + box.height / 2, { steps: 10 });
      await page.waitForTimeout(400);
    }
    await el.click(clickOpts);
  }  (e) {
    .();
     ;
  }
   page.(postClickDelay);
   ;
}

Every call should include a descriptive label for debugging.

5. Typing

Type visibly, not instant-fill:

async function typeSlowly(page, locator, text, label, charDelay = 35) {
  const el = typeof locator === 'string' ? page.locator(locator).first() : locator;
  const visible = await el.isVisible().catch(() => false);
  if (!visible) {
    console.error(`WARNING: typeSlowly skipped - "${label}" not visible`);
    return false;
  }
  await moveAndClick(page, el, label);
  await el.fill('');
  await el.pressSequentially(text, { delay: charDelay });
  await page.waitForTimeout(500);
  return true;
}

6. Scrolling

Use smooth scroll instead of jumps:

await page.evaluate(() => window.scrollTo({ top: 400, behavior: 'smooth' }));
await page.waitForTimeout(1500);

7. Dashboard Panning

When showing a dashboard or overview page, move the cursor across key elements:

async function panElements(page, selector, maxCount = 6) {
  const elements = await page.locator(selector).all();
  for (let i = 0; i < Math.min(elements.length, maxCount); i++) {
    try {
      const box = await elements[i].boundingBox();
      if (box && box.y < 700) {
        await page.mouse.move(box.x + box.width / 2, box.y + box.height / 2, { steps: 8 });
        await page.waitForTimeout(600);
      }
    } catch (e) {
      console.warn(`WARNING: panElements skipped element ${i} (selector: "${selector}"): ${e.message}`);
    }
  }
}

8. Subtitles

Inject a subtitle bar at the bottom of the viewport:

async function injectSubtitleBar(page) {
  await page.evaluate(() => {
    if (document.getElementById('demo-subtitle')) return;
    const bar = document.createElement('div');
    bar.id = 'demo-subtitle';
    bar.style.cssText = `
      position: fixed; bottom: 0; left: 0; right: 0; z-index: 999998;
      text-align: center; padding: 12px 24px;
      background: rgba(0, 0, 0, 0.75);
      color: white; font-family: -apple-system, "Segoe UI", sans-serif;
      font-size: 16px; font-weight: 500; letter-spacing: 0.3px;
      transition: opacity 0.3s;
      pointer-events: none;
    `;
    bar.textContent = '';
    bar.style.opacity = '0';
    document.body.appendChild(bar);
  });
}

async function showSubtitle(page, text) {
  await page.evaluate((t) => {
    const bar = document.getElementById('demo-subtitle');
    if (!bar) return;
    if (t) {
      bar.textContent = t;
      bar.. = ;
    }  {
      bar.. = ;
    }
  }, text);
   (text)  page.();
}

Call injectSubtitleBar(page) alongside injectCursor(page) after every navigation.

Usage pattern:

await showSubtitle(page, 'Step 1 - Logging in');
await showSubtitle(page, 'Step 2 - Dashboard overview');
await showSubtitle(page, '');

Guidelines:

• Keep subtitle text short, ideally under 60 characters.
• Use Step N - Action format for consistency.
• Clear the subtitle during long pauses where the UI can speak for itself.

Script Template

'use strict';
const { chromium } = require('playwright');
const path = require('path');
const fs = require('fs');

const BASE_URL = process.env.QA_BASE_URL || 'http://localhost:3000';
const VIDEO_DIR = path.join(__dirname, 'screenshots');
const OUTPUT_NAME = 'demo-FEATURE.webm';
const REHEARSAL = process.argv.includes('--rehearse');

// Paste injectCursor, injectSubtitleBar, showSubtitle, moveAndClick,
// typeSlowly, ensureVisible, and panElements here.

(async () => {
  const browser = await chromium.launch({ headless: true });

  if (REHEARSAL) {
    const context = await browser.newContext({ viewport: { width: 1280, height: 720 } });
    const page = await context.newPage();
    // Navigate through the flow and run ensureVisible for each selector.
     browser.();
    ;
  }

   context =  browser.({
    : { : , : { : , :  } },
    : { : , :  }
  });
   page =  context.();

   {
     (page);
     (page);

     (page, );
    

     page.();
     (page);
     (page);
     (page, );
    

     (page, );
    

     (page, );
    
     (page, );
  }  (err) {
    .(, err.);
  }  {
     context.();
     video = page.();
     (video) {
       src =  video.();
       dest = path.(, );
       {
        fs.(src, dest);
        .(, dest);
      }  (e) {
        .(, e.);
        .(, src);
        .(, dest);
      }
    }
     browser.();
  }
})();

Usage:

# Phase 2: Rehearse
node demo-script.cjs --rehearse

# Phase 3: Record
node demo-script.cjs

Checklist Before Recording

• Discovery phase completed
• Rehearsal passes with all selectors OK
• Headless mode enabled
• Resolution set to 1280x720
• Cursor and subtitle overlays re-injected after every navigation
• showSubtitle(page, 'Step N - ...') used at major transitions
• moveAndClick used for all clicks with descriptive labels
• typeSlowly used for visible input
• No silent catches; helpers log warnings
• Smooth scrolling used for content reveal
• Key pauses are visible to a human viewer
• Flow matches the requested story order
• Script reflects the actual UI discovered in phase 1

Common Pitfalls

1. Cursor disappears after navigation - re-inject it.
2. Video is too fast - add pauses.
3. Cursor is a dot instead of an arrow - use the SVG overlay.
4. Cursor teleports - move before clicking.
5. Select dropdowns look wrong - show the move, then pick the option.
6. Modals feel abrupt - add a read pause before confirming.
7. Video file path is random - copy it to a stable output name.
8. Selector failures are swallowed - never use silent catch blocks.
9. Field types were assumed - discover them first.
10. Features were assumed - inspect the actual UI before scripting.
11. Placeholder select values look real - watch for "0" and "Select...".
12. Popups create separate videos - capture popup pages explicitly and merge later if needed.