HyperFrames Core

HyperFrames renders video from HTML. A composition is an HTML file whose DOM declares timing with data-* attributes, whose animation runtime is seekable, and whose media playback is owned by the framework.

This skill is the technical contract. Other concerns live in sibling skills:

• hyperframes-animation — atomic motion rules + scene blueprints + per-runtime adapters (GSAP, Lottie, Three, Anime.js, CSS, WAAPI, TypeGPU)
• hyperframes-creative — palettes, typography, narration, beat planning, audio-reactive
• hyperframes-media — TTS, Whisper transcribe, background removal, captions
• hyperframes-registry — install blocks and components (hyperframes add)
• hyperframes-cli — dev loop commands (lint / validate / preview / render)

For Tailwind v4 projects (hyperframes init --tailwind), see references/tailwind.md — the browser-runtime contract is distinct from Studio's Tailwind v3 setup.

Routing

For animation runtime specifics (GSAP API, Lottie, Three.js, etc.) go to hyperframes-animation → adapters/<runtime>.md.

Composition Structure

Two root forms; they are not interchangeable.

• Standalone (the top-level index.html) — root <div data-composition-id="…"> sits directly in <body>. No <template> wrapper. Wrapping a standalone root in <template> hides all content from the browser and breaks rendering.
• Sub-composition (a file loaded via data-composition-src) — root <div data-composition-id="…"> must be wrapped in <template>. Without the wrapper the runtime cannot extract and mount it.

⚠ Sub-composition transport rule: the runtime only clones <template> contents into the live DOM. Everything outside the template — including <head> and any <style>/<script>/<link> that lives in <head> — is discarded. Put <style> and <script> blocks inside <template>, not in <head>.

⚠ Host-id rule: in the host file, data-composition-id on the slot must exactly equal the inner template's data-composition-id and the window.__timelines["<id>"] key. Do not add -mount / -slot / -host suffixes.

See references/sub-compositions.md for the file shape, host wiring, pitfall examples, and the pre-render verification checklist.

Root must be sized (silent layout bug)

The standalone root must establish an explicitly sized box, and every ancestor between it and a height: 100% element must have a resolved height. If the root or an intermediate wrapper has no height, a flex/height:100% content container collapses to ~0 and content piles into the top-left corner (often clipping the first glyph at x=0). lint, validate, and inspect do not catch this — inspect substitutes the authored data-width/data-height for a collapsed root and reports "0 layout issues."

<body style="margin: 0">
  <div
    id="root"
    data-composition-id="main"
    data-width="1920"
    data-height="1080"
    data-duration="5"
    style="position: relative; width: 1920px; height: 1080px; overflow: hidden"
  >
    <!-- Center robustly: position:absolute + inset:0 fills the sized root regardless of
         intermediate wrappers; or use a flex container ONLY if its parent chain is sized. -->
    <section
      class="clip"
      data-start="0"
      data-duration="5"
      data-track-index="1"
      style="position: absolute; inset: 0; display: grid; place-items: center; padding: 120px 160px; box-sizing: border-box"
    >
      <h1>Title</h1>
    </section>
  </div>
</body>

Keep the padding (≥80px) on the centering container — it is the title-safe margin that stops large type touching the frame edge. See references/minimal-composition.md.

Timeline Contract (GSAP default)

Every composition registers exactly one GSAP timeline.

• Create with gsap.timeline({ paused: true }) — the player owns playback.
• Register at window.__timelines["<composition-id>"]; the key must exactly match the root's data-composition-id. Dot syntax (window.__timelines.<id> = tl) is equivalent when the id is a valid identifier; use brackets if the id contains -.
• Build the timeline synchronously during page load — not inside async, setTimeout, Promise, or event handlers. The renderer samples after page load completes; any deferred timeline construction misses the sample.
• Render duration comes from data-duration on the root, not from GSAP timeline length. Do not pad the timeline with empty tweens to set duration.
• For sub-compositions, do not manually nest sub-timelines into the host (master.add(sub)); the framework drives them independently.

For non-GSAP runtimes (Lottie / Three / WAAPI / CSS / Anime.js / TypeGPU), the equivalent contract lives in hyperframes-animation/adapters/<runtime>.md. See references/determinism-rules.md for the cross-runtime Animation Runtime Contract.

Non-Negotiable Rules

These break the renderer — or produce silent visual bugs that lint/validate/inspect do NOT catch (rules 3, 7-8). (Synchronous timeline construction is covered above in Timeline Contract.)

1. No Math.random() / Date.now() / performance.now() driving visuals — use a seeded PRNG.
2. No repeat: -1. Use repeat: Math.max(0, Math.floor(duration / cycleDuration) - 1) — floor, not ceil (ceil overshoots data-duration and trips the gsap_repeat_ceil_overshoot lint; max(0, …) avoids a negative repeat = infinite).
3. <video>/<audio> must be a direct child of the host root (index.html) — never inside a sub-comp <template>, never inside a wrapper <div>; otherwise it is never decoded and renders blank/black (silent). The framework owns playback: no video.play() / audio.play() / currentTime = …. A sub-comp cannot drive host elements (selector or querySelector), so animate host media from the main timeline at global time. See references/variables-and-media.md.
4. No gsap.set() on clip elements from later scenes (they are not in the DOM yet). Use tl.set(selector, vars, time) at or after the clip's data-start.
5. No animating display / visibility. Animate opacity / transforms; the clip lifecycle handles show/hide.
6. No <br> in body text. Let text wrap via max-width.
7. Transformed elements must be block-level + sized. transform/scaleX/scaleY is a no-op on an inline <span>, and scaling an auto-width (0px) element shows nothing → invisible bars/fills. Give them display: block/inline-block/flex-item and a real width/height (e.g. width: 100% inside a sized parent).
8. Absolutely-positioned decoratives (badges, pills, tags) that pulse or overshoot (yoyo scale, back.out) need clearance at their peak size and must not straddle an overflow: hidden edge — else they overlap a neighbor or get clipped. Position for the largest frame, not the resting one.

Editing Existing Compositions

• Read the actual files before editing.
• Preserve unrelated timing, tracks, IDs, variables, and media paths.
• Match existing composition IDs and timeline registry keys.
• When adding a clip, choose a non-overlapping data-track-index or intentionally adjust surrounding timing.
• When adding a sub-composition, verify its internal data-composition-id before wiring the host.

Validation

Use hyperframes-cli for command details.

• npx hyperframes lint passes (0 errors)
• npx hyperframes validate passes (0 console errors)
• npx hyperframes inspect passes, or overflow is intentionally marked
• Projects with sub-compositions: npx hyperframes snapshot --at <midpoints> and eyeball each frame