Animated video

Create an animated video or motion design piece rendered as an HTML page. Build a timeline-based animation with smooth transitions. Design frame-by-frame sequences with playback controls (play/pause, scrubber). Focus on visual storytelling with the Anthropic brand palette. Export-ready at a fixed aspect ratio (16:9 or 9:16). If you need to know the position of an element (eg to move a cursor or character between elements) use refs to grab the position.

ALWAYS build on the animations_v3.jsx starter for ANY animation piece — including one hosted on a design-components page (the helmet-script + x-import structure IS the starter case, not an exemption). The only exemptions: a minor animated accent inside a larger non-animation design, or the user explicitly asking you not to use the starter. Skipping the starter silently removes the user's timeline editor — scene trims, speed changes, and video export only exist when the page builds on the engine. Do NOT load animations.jsx or animations-v2.jsx alongside it (the engines share window globals — last wins). A project that already uses an older starter keeps it; don't migrate existing animations.

START by calling copy_starter_component with kind: "animations_v3.jsx" — the continuous-composition engine: the whole animation is ONE element tree rendered from one authored-time clock, so elements move, morph, and persist across section boundaries by ordinary interpolation — nothing mounts or unmounts at a boundary. It gives you <CompositionStage>, useComposition() (→ {T, CUES}), <Shot>, <Captions>, an Easing library, and interpolate() / animate() tweens. Read the file after copying.

THE AUTHORING CONTRACT (it's in the file's usage block; follow it exactly): declare the scene list as a JSON string literal in a plain inline <script> of the MAIN document — <script>window.OM_SCENES = '[{"name":"Opening","dur":3},…]';</script> (exact JSON.stringify formatting, no spaces) — NOT in a text/babel script and NOT in a sibling .jsx (only vanilla inline script literals are addressable for the editor's write-back); declare window.OM_PLAYBACK the same way; pass both through untouched as <CompositionStage scenes={window.OM_SCENES} playback={window.OM_PLAYBACK}> wrapping ONE component — the whole piece. The scene list is the user-control view (names, order, playback durations); the engine derives the cue table from it, so the literal is the single source of structure. The user edits timing on the host timeline — trim a scene's edge, or set a section's speed — and every edit writes back into your literal and reflows the composition live.

CUE-FIRST DISCIPLINE (this is what makes a piece read as one continuous video):

1. Write the OM_SCENES literal FIRST — it is the piece's outline. Get {T, CUES} from useComposition() and key ALL choreography to T and CUES.SectionName (authored seconds) — never to your own clock, never to wall-clock time.
2. One helper component per section for readability, but ALL of them render ALL the time inside the one tree, keyed to cues — never conditionally mounted per section. A shared element crossing a boundary is just motion whose start and end straddle a cue.
3. Define exactly three motion helpers up front (e.g. MOTION = {enter, draw, pop} wrapping Easing curves) and use no easing or transform outside them; one caption element, one visible at a time (<Captions> has this built in).

TIMING IS USER-EDITABLE (time-stretch): when the user trims or speeds a section, the engine replays that section's SAME authored slice over the new playback length — choreography keyed to T retimes, never cuts off. Authored hard cuts are content now, not structure: wrap a shot's elements in <Shot from={CUES.X} to={CUES.Y}> (visibility flips at the cues; children stay mounted so images and videos hold their readiness). A looping piece shows its last authored frame immediately before its first — make them match.

Give every motion project a tweaks panel (kind: "tweaks_panel.jsx") whose TWEAK_DEFAULTS include "motionEditor": true with a <TweakToggle label="Motion editor"> wired to it. That key is the host timeline editor's visibility gate: the user flips it in the Tweaks panel to hide or show the editor bar, and the animation, its timing data, and export are untouched either way. Declare the TWEAK_DEFAULTS literal in a plain inline <script> of the MAIN document (the /EDITMODE-BEGIN/ convention), so the flip persists.