Motion across beats and seams

Served checks: picsart_scene_check_contracts runs contract records and reusable templates, picsart_scene_check_motion runs frame-complete motion records, and picsart_scene_inspect pages large sources; the one remaining limit is that pixel records have no automated checker, so inspect full-resolution rendered frames for them.

This skill owns the relationship between consecutive beats or scenes. Use motion-intent for the purpose and hierarchy inside one beat, scene-animation-reference after the motion is decided and needs scene syntax, and custom-transitions only when the current transition catalog cannot express an already-decided seam.

Keep three kinds of statement separate:

• scene fact — behavior defined by the format, validator, resolver, or authoring tools.
• Motion heuristic — a useful continuity trial that must be judged in the actual sequence.
• Project choice — a local editorial or brand decision.

Direction, velocity matching, overlap, and holds are motion heuristics, not rules enforced by the scene format. A hard cut, crossfade, direction change, or moment of stillness can be exactly right when the communication calls for interruption, ambiguity, atmosphere, punctuation, or a chapter reset.

Decide each boundary in this order

1. Name the semantic relationship

Choose the verb before the mechanism:

If the relationship is unclear, a transition name will not make it clear. State the intended relationship in one sentence first.

2. Choose a contextual vector

For continuation, first try carrying the dominant travel direction or the apparent momentum through the seam. For arrival or reset, reducing motion or changing direction may communicate the meaning better. Reading direction, subject movement, layout, and camera logic all affect the choice; there is no universal rule that right means progress or that matched velocity is always desirable.

Record the trial as a project decision, for example: “The card continues upward because the next arrangement reveals content below it.” Do not describe the decision as a scene requirement.

3. Choose the representation

Use the smallest scene structure that preserves the intended relationship:

scene fact: a track transition resolves the outgoing last frame and incoming first frame into the transition's source and destination slots. It does not preserve arbitrary live animation from the neighboring clips through the transition window. If live identity matters, prefer one persistent layer or author the motion inside a composition that remains alive.

Two copies of an apparently shared element can be appropriate when they are not semantically the same object, or when independent content constraints prevent one layer from spanning the interval. Do not duplicate only to avoid planning the layer lifetime.

Two areas of one set need no cut. Lay them out in one timeline and travel the composition camera between them: the next subject stands off-frame by construction (check every earlier frame), keeps an idle while unseen, and is revealed by the move, with its first line landing as the camera settles. A pull-back to a wide two-shot lets one character's reaction read during the other's line.

Only hand a custom transition to custom-transitions after the semantic relationship, vector or reset, and any visual carrier are decided and the shipped catalog has been checked. The custom definition must then pass its own full-window five-sample gate. Claims of duration independence need two materially different durations; claims of aspect independence need 16:9 and 9:16 evidence.

4. Identify the visual carrier

Name the thing the eye can follow: a persistent card, edge, colour field, line, subject, or directional flow. A carrier is optional. A deliberate reset may work because nothing crosses it.

When a carrier exists:

• keep its identity, trajectory, or visual role legible across the boundary;
• keep subordinate motion from becoming a second competing handoff;
• avoid making the carrier re-enter as if it were new unless that repetition is meaningful.

5. Align cause and reaction

When one action is meant to cause another, give them one authored event time. The action can prepare before the event and each response can settle on its own schedule, but the first visible press, response, and reveal should share the causal boundary unless the interface or story intentionally models latency.

This is a motion heuristic. scene permits any keyframe times; causality is the author's communication decision.

6. Plan stillness and readability

Stillness is part of continuity. Hold long enough for recognition, reading, or contrast with the next action. Remove a dead gap that communicates nothing, but keep a quiet interval that lets the sequence land. Do not use a fixed hold ratio as if it were a format constraint.

7. Audit the whole sequence

Review the connected sequence, not isolated clips:

• Does a direction reverse accidentally, or does the reversal communicate interruption or return?
• Does a carrier duplicate, disappear, or re-enter without explanation?
• Does a beat start before the previous leader has released attention?
• Is there a dead gap, or an intentional readable hold?
• Is one causal action followed by a visible reaction?
• Does the sequence settle or cut intentionally instead of merely running out of keyframes?

Change one variable at a time when diagnosing a seam. A smoother curve cannot repair a wrong semantic relationship, and a more elaborate transition cannot repair duplicated identity.

Evidence gate

Check an explicit geometry handoff

When two authored roles should occupy the same box on opposite sides of a seam, save a named handoff assertion in the contract sidecar. Unlike same-frame companion checks, it compares each role at its own root-time moment. This complete example needs query targets out and in:

{
  "version": 1,
  "timeSpace": "root",
  "contracts": [{
    "id": "card-seam",
    "description": "Incoming card occupies the outgoing card's last intended box.",
    "moments": { "outgoing": 1.99, "incoming": 2 },
    "assert": { "kind": "handoff", "outgoing": { "id": "out" }, "incoming": { "id": "in" }, "tolerancePx": 1 }
  }]
}

Check it as a handoff contract with picsart_scene_check_contracts, with explicit outgoing and incoming moments, or use picsart_scene_query_layout separately at those moments and compare each box edge with the independent design requirement. An outgoing layer ending at 2 seconds is not alive at exactly 2: choose its intended last visible frame, not an arbitrary epsilon. A moving last frame differs from an extrapolated endpoint. Use actual query composition scopes to disambiguate repeated ids; a handoff verdict covers only those two moments.

Read the named status and handoff.outgoing / handoff.incoming: both timestamped observations are returned even on a pass. maxErrorPx is the largest absolute left/top/right/bottom edge difference in root pixels. Thus same-center size jumps fail too. Both boxes must be usable, on-canvas and unrotated; missing/ambiguous/rotated/unavailable geometry is inconclusive, while a known absent role fails. One checkedSamples means one compared pair, not an inspected interval.

Use this only when geometry equality is the intended design. Intentional morphing, directional travel or a chapter reset need not match boxes. Matching geometry does not establish semantic identity, paint visibility, velocity or absence of a gap between the moments. For interval coverage, add appropriate presence checks and inspect the rendered seam. A persistent layer can be compared at distinct moments; comparing the same resolved target to itself at one moment is not a meaningful handoff. picsart_scene_diff_layouts remains useful for exploratory deltas, but its classification (for example restyled) is not a named design-contract verdict.

How it pairs layers, each pair's matchedBy: explicit matchHints first (hint); then the same content id and kind, the same asset or text (content); then the same layer id and kind however far it moved, a child by its own id under parents already paired, unless its content id differs (id); then geometry, best IoU or nearest centre (geometry). An internal layer pairs only with an internal one. Deltas are centre-based. It does not compare numeric opacity: restyled is a change of visibility, rotation or paint order. Text boxes are font-metric envelopes, not glyph bounds, so text deltas are approximate; boards whose comparable layers do not pair report unrelated.

The tolerance is for edges, not independent center/width/height tolerances: a centered width change of 2 px moves each edge by 1 px and can pass tolerancePx:1. If the design specifies separate dimension tolerances, report that unsupported intent rather than claiming this check is equivalent. In each role observation, available means the query sample exists; use matches and the named status to establish whether the target resolved. available:true with matches:0 is not a match.

Choose evidence for the claim

Use evidence appropriate to the claim:

1. Validate structure with picsart_scene_validate.
2. Query before, exactly at and after the seam. Use picsart_scene_lint_layout for supported presence, companion translation, containment and equal-opacity relationships in declared windows. Inspect every relationship result, even if collision findings are empty. Geometric presence does not prove paint visibility; equal evaluated opacity does not prove identity or absence of occlusion. Intentional crossfades need not match opacity. Run the same relationships as a contract record with picsart_scene_check_contracts when they must be replayed; retain unsupported comparisons as unchecked.
3. Inspect full-resolution picsart_scene_contact_sheet images of approach, seam and settled tail; set resolution to the scene dimensions and use at most 8 times per call.
4. Watch continuous exported video for perceived direction, velocity, causality and continuity. See linked-element-motion for shared ownership, resize and containment.

Validation and layout prove structure and geometry. They do not prove that a seam feels smooth, decisive, playful, or restrained. Those remain contextual visual judgments. Record the scene, times, and inspected artifact so a tested construction is not mistaken for universal motion law.

Hand off to the neighboring skills

• For one beat's communication goal, leader, character, and diagnosis, use motion-intent (fetch with picsart_scene_recipe, name motion-intent).
• For transforms, tracks, easing, expressions, blur, and transition placement, use scene-animation-reference (fetch with picsart_scene_recipe, name scene-animation-reference).
• For compact, reusable constructions, use motion-pattern-library (fetch with picsart_scene_recipe, name motion-pattern-library).
• For a new transition definition after the relationship is decided and the catalog has been ruled out, use custom-transitions (fetch with picsart_scene_recipe, name custom-transitions).
• When velocity, path or overlap requires measurement, record the actual evidence available. picsart_scene_check_motion measures evaluated geometry per output frame, but painted motion in exported video is not tracked automatically; measurement informs the continuity decision but does not make it.

Research note: this guidance was independently authored for scene from general motion-design principles and local evaluation. Hyperframes was reviewed as research inspiration; its wording, code, examples, values, and organization were not adopted.