nexu-io__open-design/design-templates/hyperframes/references/captions.md

Captions

Language Rule (Non-Negotiable)

Never use .en models unless the user explicitly states the audio is English. .en models TRANSLATE non-English audio into English instead of transcribing it.

1. User says the language → --model small --language <code> (no .en)
2. User says English → --model small.en
3. Language unknown → --model small (no .en, no --language) — auto-detects

---

Analyze spoken content to determine caption style. If user specifies a style, use that. Otherwise, detect tone from the transcript.

Transcript Source

[
  { "text": "Hello", "start": 0.0, "end": 0.5 },
  { "text": "world.", "start": 0.6, "end": 1.2 }
]

For transcription commands, whisper models, external APIs, see transcript-guide.md.

Style Detection (When No Style Specified)

Read the full transcript before choosing. Four dimensions:

1. Visual feel — corporate→clean; energetic→bold; storytelling→elegant; technical→precise; social→playful.

2. Color palette — dark+bright for energy; muted for professional; high contrast for clarity; one accent color.

3. Font mood — heavy/condensed for impact; clean sans for modern; rounded for friendly; serif for elegance.

4. Animation character — scale-pop for punchy; gentle fade for calm; word-by-word for emphasis; typewriter for technical.

Per-Word Styling

Scan for words deserving distinct treatment:

• Brand/product names — larger size, unique color
• ALL CAPS — scale boost, flash, accent color
• Numbers/statistics — bold weight, accent color
• Emotional keywords — exaggerated animation (overshoot, bounce)
• Call-to-action — highlight, underline, color pop
• Marker highlight — for beyond-color emphasis, see css-patterns.md

Script-to-Style Mapping

Tone	Font mood	Animation	Color	Size
Hype/launch	Heavy condensed, 800-900	Scale-pop, back.out(1.7), 0.1-0.2s	Bright on dark	72-96px
Corporate	Clean sans, 600-700	Fade+slide, power3.out, 0.3s	White/neutral, muted accent	56-72px
Tutorial	Mono/clean sans, 500-600	Typewriter/fade, 0.4-0.5s	High contrast, minimal	48-64px
Storytelling	Serif/elegant, 400-500	Slow fade, power2.out, 0.5-0.6s	Warm muted tones	44-56px
Social	Rounded sans, 700-800	Bounce, elastic.out, word-by-word	Playful, colored pills	56-80px

Word Grouping

• High energy: 2-3 words. Quick turnover.
• Conversational: 3-5 words. Natural phrases.
• Measured/calm: 4-6 words. Longer groups.

Break on sentence boundaries, 150ms+ pauses, or max word count.

Positioning

• Landscape (1920x1080): Bottom 80-120px, centered
• Portrait (1080x1920): Lower middle ~600-700px from bottom, centered
• Never cover the subject's face
• position: absolute — never relative
• One caption group visible at a time

Text Overflow Prevention

Use window.__hyperframes.fitTextFontSize():

var result = window.__hyperframes.fitTextFontSize(group.text.toUpperCase(), {
  fontFamily: "Outfit",
  fontWeight: 900,
  maxWidth: 1600,
});
el.style.fontSize = result.fontSize + "px";

Options: maxWidth (1600 landscape, 900 portrait), baseFontSize (78), minFontSize (42), fontWeight, fontFamily, step (2).

CSS safety nets: max-width on container, overflow: visible (not hidden — hidden clips scaled emphasis words and glow effects), position: absolute, explicit height. When per-word styling uses scale > 1.0, compute maxWidth = safeWidth / maxScale to leave headroom.

Container pattern: Full-width absolute container, centered. Do not use left: 50%; transform: translateX(-50%) — causes clipping at composition edges.

Caption Exit Guarantee

Every group must have a hard kill after exit animation:

tl.to(groupEl, { opacity: 0, scale: 0.95, duration: 0.12, ease: "power2.in" }, group.end - 0.12);
tl.set(groupEl, { opacity: 0, visibility: "hidden" }, group.end); // deterministic kill

Self-lint after building timeline — place before window.__timelines[id] = tl so it runs at composition init:

GROUPS.forEach(function (group, gi) {
  var el = document.getElementById("cg-" + gi);
  if (!el) return;
  tl.seek(group.end + 0.01);
  var computed = window.getComputedStyle(el);
  if (computed.opacity !== "0" && computed.visibility !== "hidden") {
    console.warn(
      "[caption-lint] group " + gi + " still visible at t=" + (group.end + 0.01).toFixed(2) + "s",
    );
  }
});
tl.seek(0);

Further References

• dynamic-techniques.md — karaoke, clip-path reveals, slam words, scatter exits, elastic, 3D rotation
• transcript-guide.md — transcription commands, whisper models, external APIs
• css-patterns.md — CSS+GSAP marker highlighting (deterministic, fully seekable)

Constraints

• Deterministic. No Math.random(), no Date.now().
• Sync to transcript timestamps.
• One group visible at a time.
• Every group must have a hard tl.set kill at group.end.
• The compiler embeds supported fonts automatically — just declare font-family in CSS.