frames/skills/frames-core/SKILL.md

name, description

name	description
frames-core	The Frames composition contract — build one renderable project. Use for composition structure, the `data-*` timing attributes, `class="clip"`, tracks, sub-compositions, variables, framework-owned media playback, deterministic-render rules, and validation. Also covers Tailwind projects and the STORYBOARD.md / SCRIPT.md plan formats. Read before writing composition HTML.

Frames Core

Frames 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 — how to build one frames project. The body below is the build guide; per-topic detail lives in references/ (index next), read on demand. Other concerns live in the sibling domain skills — frames-animation, frames-creative, media-use, frames-cli, frames-registry. The capability map in /frames says what each one covers.

References

File	Read it to…
references/minimal-composition.md	start from the smallest renderable composition skeleton
references/composition-patterns.md	choose monolithic vs modular; structure a modular index.html; pick a sub-comp archetype
references/data-attributes.md	look up any data-* (root / clip / sub-comp host / legacy aliases); use class="clip"
references/tracks-and-clips.md	pick data-track-index, handle same-track overlap / z-index, time a clip relative to another
references/sub-compositions.md	wire a sub-composition (host attrs, <template>, per-instance vars) and animate inside it
references/variables-and-media.md	declare variables; place <video>/<audio>, set volume, trim
references/determinism-rules.md	build a seekable timeline; determinism bans; the animatable-property allowlist; layout / text fit
references/full-screen-motion.md	author full-frame motion with shared backgrounds
references/storyboard-format.md	author a STORYBOARD.md plan (+ the parsed manifest)
references/review-loop.md	run the plan → sketch → build review passes on a live board — shared by every storyboard-planning workflow
references/production-loop.md	take an approved plan to a delivered video — the stage dependencies (audio, frames, assembly, transitions, captions, verify, deliver) a freeform build follows directly
references/brief-contract.md	the brief's ground rules — mode derivation (collaborative / autonomous), shared field registry, question invariants (the asking itself lives in /frames → the intent layer)
references/brief-format.md	author BRIEF.md — the confirmed intent document a workflow's Setup writes and every later step reads
references/script-format.md	author the optional SCRIPT.md locked narration
references/subagent-dispatch.md	map subagent dispatch verbs (parallel fan-out / background / wait) to your harness
references/frame-worker-core.md	the shared frame-worker role contract — each narrative workflow's packet builder prepends it to that workflow's sub-agents/frame-worker.md delta
references/tailwind.md	work in a Tailwind v4 project (init --tailwind; runtime contract differs from Studio's v3)

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

Building a composition

Two root forms (not interchangeable)

• Standalone (top-level index.html) — root <div data-composition-id="…"> sits directly in <body>, no <template> wrapper (wrapping it hides all content and breaks rendering).
• Sub-composition (loaded via data-composition-src) — root must be wrapped in <template>.

⚠ Transport rule: the runtime only clones <template> contents; everything outside (incl. <head> styles/scripts) is discarded — put <style>/<script> inside the template. ⚠ Host-id rule: the host slot's data-composition-id must exactly equal the inner template's data-composition-id and the window.__timelines["<id>"] key — no -mount/-slot/-host suffix.

File shape, host wiring, and the pre-render checklist → references/sub-compositions.md.

Root must be sized (silent layout bug)

The standalone root needs an explicit sized box (width/height in px), and every ancestor down to a height:100% element must have a resolved height — otherwise a flex/100% child collapses to ~0 and content piles into the top-left corner. Do not rely on automated gates alone to catch this; inspect a snapshot. Skeleton → references/minimal-composition.md.

One paused timeline

Each composition registers exactly one gsap.timeline({ paused: true }) at window.__timelines["<id>"] (key = root data-composition-id), built synchronously at page load. Render duration = root data-duration, not timeline length. Don't manually nest sub-timelines into the host. Full contract (incl. non-GSAP runtimes) → references/determinism-rules.md + frames-animation/adapters/.

Non-negotiable rules (silent bugs automated gates may miss)

Surfaced here; full rationale in the linked reference. Do not violate:

• No render-time clocks / unseeded Math.random / network / input-state; no repeat: -1 (use a finite count). → determinism-rules.md
• Animate only the visual-property allowlist; never tween display or raw visibility. GSAP autoAlpha and zero-duration timeline boundary sets are the only visibility exceptions, and only on non-clip elements or wrappers inside a clip. The framework alone controls .clip visibility. Do not gsap.set later-scene clips at page load. → determinism-rules.md
• No <br> in body text; transformed elements must be block-level + sized; pulsing absolute decoratives need peak clearance. → determinism-rules.md
• <video>/<audio> work at any nesting depth (including inside a sub-comp <template> or wrapper); the framework owns playback and seeks/decodes media wherever it lives. The one caveat is timelines, not placement: a sub-comp timeline can't animate host-root elements. → variables-and-media.md
• Every id must be unique across the assembled page; inside a sub-comp, prefix ids with the composition id (#<id>-hero). Duplicate <video>/<img> ids render blank — the producer injects frames by getElementById, and cross-file dupes slip past lint. → composition-patterns.md
• A full-screen scene fill goes on a full-bleed child (position:absolute; inset:0), never on the composition root itself — the producer's frame compositing can drop the root element's own background (the frame renders black) even though preview/snapshot show it correctly. → composition-patterns.md

Editing existing compositions

• Read the files first. Preserve unrelated timing, tracks, IDs, variables, media paths.
• Match existing composition IDs and timeline keys.
• Adding a clip: pick a non-overlapping data-track-index or adjust surrounding timing intentionally.
• data-hidden on any composition element hides it in BOTH preview and render, overriding its time window; it is non-destructive/reversible and toggled by Studio's timeline eye icon.
• Adding a sub-composition: verify its internal data-composition-id before wiring the host.

Validation

Use frames-cli for command details

• npx @hanzo/frames check passes (0 findings across lint, runtime, layout, motion, and contrast)
• Projects with sub-compositions: npx @hanzo/frames snapshot --at <midpoints> and eyeball each frame
• npx @hanzo/frames preview for review (the user can edit anything in Studio's timeline)
• npx @hanzo/frames render only after the user approves