CM ReadIt — Web Audio Experience Skill

Philosophy: Reading is passive. Listening is intimate. Voice builds trust faster than any headline. Core Principle: Zero dependencies. Progressive enhancement. Respect user's device and preferences.

🎯 Selective Reading Rule (MANDATORY)

🔴 tts-engine.md = ALWAYS READ when implementing TTS. Others = only if relevant.

Quick Decision Tree

"I need audio on my website"
│
├─ Read article content aloud (text-to-speech)
│  └─ Use: TTS Engine → tts-engine.md
│     ├─ Blog / article pages → Content Reader pattern
│     ├─ Documentation → Section Reader pattern
│     └─ E-commerce → Product Description Reader pattern
│
├─ Play pre-recorded audio files (MP3/WAV)
│  └─ Use: Audio Player → audio-player.md
│     ├─ Podcasts / interviews → Playlist pattern
│     ├─ Sales pitch / welcome → Triggered playback
│     └─ Background ambient → Loop pattern
│
├─ Voice-based conversion optimization (CRO)
│  └─ Use: Voice CRO → voice-cro.md
│     ├─ Landing pages → Trigger-based bottom sheet
│     ├─ Service pages → Per-page audio scripts
│     └─ Course pages → Social proof audio
│
└─ Combination (TTS + CRO)
   └─ Read tts-engine.md + voice-cro.md
      └─ Ensure no conflict (TTS reader vs CRO player)

🧠 Core Principles (Internalize These)

1. The 3 Audio Engines

2. Progressive Enhancement

Feature detection → Graceful degradation → Never break the page

if (!('speechSynthesis' in window)) return;  // TTS
if (!window.Audio) return;                    // Audio

Rule: Audio features are ENHANCEMENTS. The page must function 100% without them.

3. Content Extraction Principle

Clone → Strip → Clean → Split → Speak

DON'T read the raw DOM.
DO clone, remove noise, extract clean text.

Strip list (always remove before speaking):

• CTAs, promotions, ads
• Navigation, footer, sidebar
• Images, videos, iframes, SVGs
• Scripts, styles, hidden elements
• Tags, badges, metadata

4. The Chunking Problem

Browsers have a hard limit on utterance length (~3000-5000 chars depending on browser/OS). Long text must be split into chunks.

Split Strategy:
├─ Split on sentence boundaries (. ! ? \n)
├─ Max chunk: 2500 chars (safe across all browsers)
├─ Preserve sentence integrity (never split mid-sentence)
└─ Chain chunks via onend callback

5. Voice Selection Priority

Language voices:
1. Local service voice (faster, works offline)
2. Network voice (higher quality, needs internet)
3. Any voice matching language prefix
4. null (browser default)

6. Chrome Keep-Alive Bug

⚠️ CRITICAL: Chrome silently stops SpeechSynthesis after ~15 seconds of continuous speech. This is the #1 gotcha.

// Workaround: pause/resume every 10s
setInterval(() => {
    if (synth.speaking && !synth.paused) {
        synth.pause();
        synth.resume();
    }
}, 10000);

7. synth.cancel() Triggers onerror

⚠️ GOTCHA: Calling synth.cancel() fires the onerror event on any active utterance with error type 'canceled' or 'interrupted'.

Solution: Use a guard flag or check error type:

u.onerror = function(e) {
    if (e.error === 'canceled' || e.error === 'interrupted') return;
    stopReading();
};

🏗️ Architecture Pattern

Minimal TTS Reader (Copy-Paste Starting Point)

┌─────────────────────────────────────────┐
│                  IIFE                    │
│                                          │
│  ┌─ Feature Detection ─┐                │
│  │  speechSynthesis?    │                │
│  └──────────┬───────────┘                │
│             ▼                            │
│  ┌─ Content Extraction ─┐               │
│  │  Clone → Strip → Clean│              │
│  └──────────┬────────────┘               │
│             ▼                            │
│  ┌─ Chunking Engine ────┐               │
│  │  Split on sentences   │              │
│  │  Max 2500 chars       │              │
│  └──────────┬────────────┘               │
│             ▼                            │
│  ┌─ Utterance Builder ──┐               │
│  │  Set voice/rate/pitch │              │
│  │  Chain via onend      │              │
│  └──────────┬────────────┘               │
│             ▼                            │
│  ┌─ Player UI ──────────┐               │
│  │  Bar: play/pause/stop │              │
│  │  Progress indicator   │              │
│  │  Trigger button       │              │
│  └──────────┬────────────┘               │
│             ▼                            │
│  ┌─ Keep-Alive Timer ───┐               │
│  │  pause/resume @ 10s  │               │
│  └───────────────────────┘               │
└──────────────────────────────────────────┘

Lifecycle

Init → Detect → Inject Trigger Button
         │
   User clicks ▶
         │
   Extract Text → Chunk → Build Utterances
         │
   synth.speak(chunk[0])
         │
   chunk[0].onend → speak(chunk[1]) → ... → speak(chunk[N])
         │                                        │
   Keep-Alive Timer running                   chunk[N].onend
         │                                        │
   User clicks ⏸ → synth.pause()             stopReading()
   User clicks ▶ → synth.resume()            cleanup UI
   User clicks ✕ → synth.cancel()

📐 Implementation Checklist

For TTS Reader

• [ ] Feature detection (speechSynthesis in window)
• [ ] Content container identified (ID or selector)
• [ ] Strip list defined (what to remove before reading)
• [ ] Chunk size set (default 2500)
• [ ] Voice selection logic (language-specific)
• [ ] Player bar UI (play/pause/close + progress)
• [ ] Trigger button injected (topbar or floating)
• [ ] Chrome keep-alive timer (10s interval)
• [ ] onerror guard (handle cancel/interrupted)
• [ ] beforeunload cleanup
• [ ] prefers-reduced-motion respect
• [ ] Mobile safe-area padding

For Audio Player

• [ ] Audio files hosted and accessible
• [ ] Preload strategy (none → load on demand)
• [ ] Play/pause toggle with state management
• [ ] Progress bar with currentTime/duration
• [ ] Error handling (network, format, autoplay policy)
• [ ] Session state (dismissed = don't show again)

For Voice CRO

• [ ] Per-page config object (delay, scroll threshold, audio URLs)
• [ ] Trigger conditions (time + scroll AND/OR interaction)
• [ ] Bottom sheet UI (icon, text, CTA, dismiss)
• [ ] Player bar UI (toggle, progress, CTA button)
• [ ] Session dismissal tracking
• [ ] Stats tracking (shown/listened/dismissed)
• [ ] No conflict with TTS Reader

⚠️ Common Pitfalls

🌐 Multi-Language Support

Voice selection by language:
├─ Vietnamese: v.lang === 'vi-VN' || v.lang.startsWith('vi')
├─ English: v.lang === 'en-US' || v.lang.startsWith('en')
├─ Japanese: v.lang === 'ja-JP' || v.lang.startsWith('ja')
├─ Korean: v.lang === 'ko-KR' || v.lang.startsWith('ko')
└─ Any: Pass language code as config parameter

Set utterance.lang to match the content language for correct pronunciation.

📚 Reference Files

🔗 Reference Implementations

Remember: Voice is the most personal interface. A well-placed audio feature can increase engagement 3-5x. But unwanted audio is the fastest way to lose a user. Always require user initiation. Never autoplay.