Setting the file. One moment.
Subchapter 21.1
references/composition-patterns.mdMarkdown11 KBView on GitHub
How to architect a project: the index.html orchestrator at scale, and the common sub-composition archetypes. Pair with minimal-composition.md (single-file shape) and sub-compositions.md (mechanics of a sub-comp file).
| Monolithic (single file) | Modular (sub-compositions) | |
|---|---|---|
| Project layout | index.html only | index.html + compositions/<scene>.html per scene |
| Where scenes live | Inline <section class="clip"> siblings under the root | Each scene is a separate file wrapped in <template> |
| Timeline registration | One timeline keyed at the root’s data-composition-id | Root timeline (often near-empty) + one timeline per sub-comp, each keyed by its id |
| Routing entry | references/minimal-composition.md | references/sub-compositions.md |
Both architectures use the same runtime contract — data-* attributes + window.__timelines[id]. The choice is structural, not behavioral.
When using sub-compositions, index.html should be thin. Its job is to declare slots, lay them out in time, mount the audio track, and register a (usually empty) root timeline. All scene animation lives inside the sub-comps.
<!doctype html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<script src="https://cdn.jsdelivr.net/npm/gsap@3.14.2/dist/gsap.min.js"></script>
<style>
body {
margin: 0;
background: #000;
}
#root {
position: relative;
width: 100%;
height: 100%;
overflow: hidden;
}
/* Sub-comp slots stretch to fill the root. */
[data-composition-id="root"] > div[data-composition-src] {
position: absolute;
inset: 0;
}
</style>
</head>
<body>
<div
id="root"
data-composition-id="root"
data-width="1920"
data-height="1080"
data-duration="30"
>
<!-- Sequential scenes — each one a sub-composition slot. -->
<div
id="el-intro"
data-composition-id="intro"
data-composition-src="compositions/intro.html"
data-start="0"
data-duration="6"
data-track-index="1"
></div>
<div
id="el-body"
data-composition-id="body"
data-composition-src="compositions/body.html"
data-start="6"
data-duration="18"
data-track-index="1"
></div>
<div
id="el-outro"
data-composition-id="outro"
data-composition-src="compositions/outro.html"
data-start="24"
data-duration="6"
data-track-index="1"
></div>
<!-- Continuous audio at the root — survives scene cuts. -->
<audio
id="el-bgm"
src="assets/bgm.mp3"
data-start="0"
data-duration="30"
data-track-index="10"
data-volume="0.6"
></audio>
</div>
<script>
window.__timelines["root"] = gsap.timeline({ paused: true });
</script>
</body>
</html>Key properties of this layout:
data-track-index (e.g. 1), authored sequentially. For a cross-fade, overlap their times by the fade duration; giving the incoming scene its own track keeps Studio’s timeline readable, but the render accepts an overlap either way.10). Keeps the linter’s overlap rules clear of any visual collisions.el-<name> or <scene-id>. The slot’s data-composition-id must still equal the sub-comp’s internal id (see sub-compositions.md).The sub-comp contains the scene’s full DOM, scoped CSS, and timeline. This is the standard pattern in sub-compositions.md — most scenes are this.
<video>/<audio> seek and decode at any nesting depth, so a scene-specific clip can live inside its scene’s sub-comp with scene-local data-start and be driven by that sub-comp’s own timeline. Use this host-media pattern instead when you want the media’s motion authored on the main timeline: put the <video>/<audio> as a host-root sibling positioned over the scene’s frame.
The reason to reach for it: a sub-comp timeline cannot drive host elements (a global selector or document.querySelector does not resolve across the boundary). So if the media lives at the host root, author its per-scene motion (scale/opacity/morph/tilt/breathing) on the main timeline in index.html, at global time = scene-local time + the scene slot’s data-start.
<!-- index.html (host) -->
<div
id="el-final"
data-composition-id="final-anim"
data-composition-src="compositions/final-anim.html"
data-start="20"
data-duration="6"
data-track-index="1"
></div>
<!-- media is a DIRECT root child; sits over the sub-comp's frame -->
<video
id="final-video"
class="clip"
src="assets/final.mp4"
data-start="20"
data-duration="6"
data-track-index="2"
muted
playsinline
style="position:absolute; left:360px; top:100px; width:1200px; height:680px; object-fit:cover; border-radius:24px;"
></video>
<script>
// MAIN timeline drives the host video. Global time: scene starts at 20.
const main = window.__timelines["main"];
main.fromTo(
"#final-video",
{ scale: 1.4, filter: "blur(14px)" },
{ scale: 1.0, filter: "blur(0px)", duration: 0.9, ease: "power3.out" },
20,
); // = slot data-start (+ any scene-local offset)
</script>
<!-- compositions/final-anim.html — frame/shell only, no <video>, no host-element animation -->
<template>
<div
data-composition-id="final-anim"
data-width="1920"
data-height="1080"
data-duration="6"
style="position:absolute; inset:0; pointer-events:none;"
>
<script>
const tl = gsap.timeline({ paused: true });
// animate ONLY this sub-comp's own elements here (labels, frame, overlays)
window.__timelines["final-anim"] = tl;
</script>
</div>
</template>Caveats:
index.html, so the main timeline’s selector resolves it. (Media nested in a sub-comp is also driven fine; it just can’t be reached by the main timeline’s selectors — drive it from the sub-comp’s own timeline.)[data-start, data-start+data-duration] window. The main-timeline opacity/scale tweens compose with it fine; for an opacity reveal/crossfade prefer a host wrapper so you are not fighting the lifecycle on the media element itself.src + data-start trigger duplicate_media_discovery_risk (benign — both still render).When several beat-level scenes share continuous state — a chat thread that grows, a persistent headline word that carries across the cut, a single canvas with internal phase changes — collapse them into one sub-comp and use internal phase divs rather than multiple sub-comp slots.
<!-- compositions/act2-merged.html -->
<template>
<div data-composition-id="act2-merged" data-width="1920" data-height="1080" data-duration="9">
<style>
[data-composition-id="act2-merged"] .phase {
position: absolute;
inset: 0;
opacity: 0;
}
</style>
<div class="phase" id="phase-a">…</div>
<div class="phase" id="phase-b">…</div>
<div class="phase" id="phase-c">…</div>
<script>
const tl = gsap.timeline({ paused: true });
tl.set("#phase-a", { opacity: 1 }, 0);
tl.to("#phase-a", { opacity: 0, duration: 0.4 }, 3.0);
tl.set("#phase-b", { opacity: 1 }, 3.0);
// …
window.__timelines["act2-merged"] = tl;
</script>
</div>
</template>Reach for this over multiple sequential slots when scenes share DOM, share a canvas, or need to cross-fade with persistent elements (a headline that survives the cut between phases). Each phase is just a div inside the same sub-comp — the parent timeline never has to know about the internal phase boundaries.
Audio always lives at the host (index.html) as a root-level <audio> so playback survives scene cuts. A sub-comp that visualizes audio should read a pre-baked frequency curve at init, then sample the baked curve from its timeline — the visual must still be a deterministic function of tl.time(), not of audio.currentTime. See determinism-rules.md and hyperframes-creative for the authoring pattern.
| Thing | Convention | Example |
|---|---|---|
| Sub-comp file | compositions/<scene-id>.html | compositions/act0-intro-bell.html |
Sub-comp <template> id (optional) | <scene-id>-template | <template id="act0-intro-bell-template"> |
Sub-comp root data-composition-id | <scene-id> (must match host slot) | data-composition-id="act0-intro-bell" |
| Timeline registry key | matches data-composition-id | window.__timelines["act0-intro-bell"] |
Host slot id | el-<short> or <scene-id> | id="el-intro", id="act0" |
| Element ids inside a sub-comp | prefix with the scene id | #act0-bell, #b1-tape |
| Audio at root | data-track-index well above visual tracks | 10 while visuals use 1 |
The -template suffix on <template> is conventional but not required — the runtime extracts contents from whichever <template> is in <body>, regardless of id. The prefix on inner element ids is the only safeguard against id collisions when multiple sub-comps are mounted into the same host page at once.