Product Demo Video Creator

Create polished demo videos with voiceover and text overlays — fully automated, zero cost.

Stack

Quick Start

1. Install dependencies (see scripts/install-deps.sh)
2. Define scenes in scripts/record-demo.mjs (copy template, customize)
3. Run: node scripts/record-demo.mjs
4. Output: MP4 with voiceover + text overlays

Workflow

Define Scenes → Generate Voiceover → Record Browser → Add Text Overlays → Compile Video
     ↓               ↓                    ↓                  ↓                ↓
  scenes[]      edge-tts MP3      Puppeteer frames     PIL drawtext      FFmpeg concat

Step 1: Define Scenes

Each scene has: id, title, subtitle, narration, url, type, actions.

{
  id: 'json',
  title: 'JSON Formatter',
  subtitle: 'Paste messy JSON, get formatted output',
  narration: 'Paste any messy JSON and get it formatted instantly.',
  url: 'https://example.com/json-formatter/',
  type: 'tool',       // 'intro' | 'tool' | 'outro'
  actions: async (page) => {
    await reactSetValue(page, 'textarea', '{"key":"value"}');
    await wait(1000);
    await clickButton(page, ['Format']);
    await wait(2000);
  }
}

Step 2: Scene Types and Overlay Positioning

Critical: Use bottom bar, not top bar — top overlays conflict with website navigation.

Step 3: React App Interaction

React controlled components ignore direct .value assignment. Use reactSetValue():

async function reactSetValue(page, selector, value) {
  await page.evaluate((sel, val) => {
    const el = document.querySelector(sel);
    const setter = Object.getOwnPropertyDescriptor(
      el.tagName === 'TEXTAREA'
        ? window.HTMLTextAreaElement.prototype
        : window.HTMLInputElement.prototype, 'value'
    )?.set;
    if (setter) setter.call(el, val);
    else el.value = val;
    el.dispatchEvent(new Event('input', { bubbles: true }));
    el.dispatchEvent(new Event('change', { bubbles: true }));
  }, selector, value);
}

Step 4: Voiceover

edge-tts --voice en-US-AndrewNeural --rate=+5% --text "Your narration" --write-media output.mp3

Recommended voices:

• en-US-AndrewNeural — Male, warm, confident (best for product demos)
• en-US-AriaNeural — Female, positive, confident
• en-US-BrianNeural — Male, approachable, casual

Step 5: Text Overlays

PIL adds text to frames. Key design rules:

• Solid dark background (alpha ≥ 230) — semi-transparent looks cheap
• Green accent line (2px) separating bar from content
• "100% Client-Side" or equivalent badge in green (#4ade80)
• Font: Noto Sans Bold for titles, Regular for subtitles

Step 6: Video Compilation

# Frames to video per scene
ffmpeg -framerate 6 -i frames/frame_%05d.png -c:v libx264 -preset slow -crf 20 -pix_fmt yuv420p -r 24 scene.mp4

# Add audio
ffmpeg -i scene.mp4 -i narration.mp3 -c:v copy -c:a aac -b:a 128k -shortest scene_final.mp4

# Normalize for concatenation
ffmpeg -i scene_final.mp4 -c:v libx264 -preset slow -crf 20 -r 24 -c:a aac -b:a 128k -ar 44100 -ac 2 scene_norm.mp4

# Concatenate
ffmpeg -f concat -safe 0 -i concat.txt -c copy output.mp4

Timing Guidelines

Scene duration = max(8s, ceil(audio_duration) + 2s)

Capture Settings

Troubleshooting

• Empty tool outputs: React apps need reactSetValue(), not .value =
• Dropdown menus open: Click body after interactions to dismiss
• FFmpeg "No such filter: drawtext": Static FFmpeg builds lack it — use PIL instead
• edge-tts fails: Check network; it calls Microsoft servers
• Chromium won't start: Need --no-sandbox --disable-gpu --disable-dev-shm-usage

References

• references/demo-planning.md — Demo structure, pacing, what makes demos compelling
• scripts/record-demo.mjs — Complete working template (customize scenes for your app)
• scripts/overlay.py — PIL text overlay processor
• scripts/install-deps.sh — One-command dependency setup