name: hyperframes-core description: The HyperFrames 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. Read before writing composition HTML. ---

Plugin installs: Before setup or freshness commands, follow plugin execution rules when this skill is inside a HyperFrames plugin. Standalone installs keep the update instructions below.

HyperFrames Core

Agent pitfalls (read first):

• Center with flex/inset, not CSS transform: translate(-50%,-50%) on a node you then GSAP x/y. Lint: gsap_css_transform_conflict. Use fromTo or xPercent/yPercent.
• Do not add a scene-exit tl.set(..., {visibility:"hidden"}). The runtime already hides timed clips. Opacity fades on inner nodes (or opacity on .clip) are enough. Caption hard-kills are a different rule.
• window.__timelines["id"] must match the root data-composition-id.
• After render, read the summary's second line: beginframe vs screenshot, GPU mode, stage timings. screenshot + software gpu on Linux is the slow path.

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 — how to build one hyperframes project. The body below is the build guide; per-topic detail lives in references/ (index next), read on demand. Process docs (brief, storyboard, review, production, dispatch, frame-worker) live in /hyperframes → references/. Other concerns live in the sibling domain skills — hyperframes-animation, hyperframes-creative, media-use, hyperframes-cli, hyperframes-registry. The capability map in /hyperframes says what each one covers.

References

For animation runtime specifics (GSAP API, Lottie, Three.js, etc.) go to hyperframes-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 a standalone root hides all content and lint rejects it (standalone_composition_wrapped_in_template, error).
• Sub-composition (loaded via data-composition-src): wrap the root in <template>. This is the shape to write: the loader also accepts a plain full document and falls back to its <body>, but the templated form is what the examples and tooling assume.

⚠ Transport rule: for a templated sub-composition the assembler drops the file's own <head> <style>/<script> (packages/core/src/compiler/compositionAssembly.ts, the hasTemplate gate), so put <style>/<script> inside the template. <link> is hoisted either way. ⚠ Host-id convention: give the host slot, the inner template, and the window.__timelines["<id>"] key the same id. A different local id is supported (the assembler falls back to the first root in the file) but the mismatch is silent, so match them unless you have a reason not to.

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

Root must be sized (silent layout bug)

The standalone root authors width/height: 100%. Canvas size is data-width/data-height. The runtime stamps those pixels onto the composition root. Do not hardcode 1920px/1080px on #root. 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). Building it inside an async callback (document.fonts.ready) is supported; what matters is that you register only after the build completes. Render length is the root's data-duration, not the timeline's length: a timeline that runs past it is cut off, and one that ends early holds its last frame. Omit the root data-duration and the length is inferred instead (timeline, media window, or adapter). You do not need window.__timelines = window.__timelines || {}: the runtime creates the registry before your inline scripts run, and lint no longer asks for it. Don't manually nest sub-timelines into the host; the runtime auto-nests registered child timelines. Full contract (incl. non-GSAP runtimes) → references/determinism-rules.md + hyperframes-animation/adapters/.

First-pass lint gotchas (a guaranteed first build failure)

Rules that lint does catch, but only after the fact. Write them right the first time:

• Never pair a CSS initial transform with a GSAP tween on the same property — the CSS value and the tween's start fight and lint rejects it with gsap_css_transform_conflict. Set the initial state inside the tween with gsap.fromTo(el, { x: -40 }, { x: 0 }) instead of a CSS transform: translateX(-40px).
• Never put crossorigin on <video>/<audio>. lint rejects it unconditionally with media_crossorigin_breaks_preview (error), including for canvas/WebGL/WebAudio readback. There is no suppression.
• Never give a <video data-start> an ancestor that also carries data-start. lint rejects it with video_nested_in_timed_element (error). Time the wrapper or the video, not both.
• Every <audio> needs an id. lint rejects it with media_missing_id, and an id-less <audio> is never picked up by the mixer, so the render is silent.
• Never tween a .clip with autoAlpha or visibility — lint rejects it with gsap_animates_clip_element. Animate a child instead.
• A named CSS font-family needs an in-file @font-face to a shipped local file, or lint fires font_family_without_font_face.
• Sub-composition #root uses width/height: 100% (or inset: 0), not hardcoded 1920px/1080px. Canvas size is data-width/data-height.

A lint error also switches off the layout and contrast audits: check then reports 0 sample(s) and 0/0 text checks, which reads like a clean file but means nothing ran. Clear lint errors before you trust those numbers.

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; repeat: -1 only under a finite root data-duration (export clips to it — otherwise use a finite count). → determinism-rules.md
• Never tween display, visibility, or autoAlpha on a .clip element. The framework owns clip visibility, and lint rejects it (gsap_animates_clip_element). Animate a child instead. → 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> are found by a flat document query, so the framework seeks and decodes them at any nesting depth (including inside a sub-comp <template> or wrapper). One hard limit: lint errors if a <video data-start> sits inside another plain element that also has data-start, and the failure is real (wrong source frames, then the clip vanishes mid-slot), so put the timing on the wrapper or on the video, never both. Sub-composition hosts are exempt: media inside a sub-composition renders correctly. The other caveat is timelines, not placement: a sub-comp timeline can't animate host-root elements. → variables-and-media.md
• Keep every id unique across the assembled page (prefix sub-comp ids with the composition id, #<id>-hero) so your own #id CSS and getElementById calls resolve. Frame injection no longer depends on it: the compiler stamps a document-unique data-hf-render-id on every video[src]/audio[src]/img[src]. Media that uses <source> children instead of a src attribute is not stamped, so unique ids still matter there. → composition-patterns.md
• A full-screen fill on the composition root is fine on a normal render. It is dropped only on the layered-composite path (HDR content, or a composition using shader transitions), where the engine forces every composition root transparent so the layer beneath shows through. If your composition uses shader transitions or HDR media, put the fill on a full-bleed child (position:absolute; inset:0). → composition-patterns.md

Editing existing compositions

• Read the files first. Preserve unrelated timing, tracks, IDs, variables, media paths.
• To know what is on a project's timeline (tracks, clips, starts, ends, what plays), run npx hyperframes timeline [--json] instead of reading index.html and every sub-composition file.
• Match existing composition IDs and timeline keys.
• Adding a clip: set its data-start/data-duration intentionally against the clips around it. data-track-index is a Studio display lane, not a timing constraint, so it does not need to be free.
• A clip that ends past the root data-duration is cut off: extend the root data-duration to the clip's end in the same edit (lint warns clip_ends_past_root_duration).
• A clip nested inside another timed element counts its data-start from the composition, not from that element, and shows only while that element shows. timeline lists it under its parent and warns never visible when the windows miss (lint reports nested_clip_never_visible).
• 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 hyperframes-cli for command details

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