heygen-com · miguel-heygen · Jun 18, 2026
diff --git a/packages/core/src/runtime/init.ts b/packages/core/src/runtime/init.ts
@@ -410,23 +410,6 @@ export function initSandboxRuntimeModular(): void {
     return resolveStartForElement(element, fallback);
   };
 
-  const findTimedClipAncestor = (
-    element: HTMLElement,
-    rootComp: HTMLElement | null,
-  ): HTMLElement | null => {
-    let node = element.parentElement;
-    while (node) {
-      // rootComp may be null when no composition is mounted; the walk still
-      // terminates via `while (node)` — node === null is never true here.
-      if (node === rootComp) break;
-      if (node.hasAttribute("data-start")) {
-        return node;
-      }
-      node = node.parentElement;
-    }
-    return null;
-  };
-
   const isTimedElementVisibleAt = (rawNode: HTMLElement, currentTime: number): boolean => {
     const tag = rawNode.tagName.toLowerCase();
     if (tag === "script" || tag === "style" || tag === "link" || tag === "meta") {
@@ -1073,6 +1056,21 @@ export function initSandboxRuntimeModular(): void {
       const dur = String(rootDuration > 0 ? rootDuration : 1);
       const seen = new Set<Element>();
 
+      // Only an AUTHORED clip (data-start already in the source, captured before
+      // we stamp anything) should suppress stamping its descendants. An animated
+      // scene container we auto-stamp below (e.g. an opacity-crossfaded scene)
+      // must NOT suppress its own animated children — otherwise those children
+      // never become timeline clips and that scene can't inline-expand.
+      const authoredTimed = new Set<Element>(document.querySelectorAll("[data-start]"));
+      const hasAuthoredTimedAncestor = (element: HTMLElement): boolean => {
+        let node = element.parentElement;
+        while (node && node !== rootComp) {
+          if (authoredTimed.has(node)) return true;
+          node = node.parentElement;
+        }
+        return false;
+      };
+
       // Stamp GSAP-targeted elements
       if (state.capturedTimeline.getChildren) {
         try {
@@ -1082,7 +1080,7 @@ export function initSandboxRuntimeModular(): void {
               if (!(target instanceof HTMLElement)) continue;
               if (target === rootComp) continue;
               if (target.hasAttribute("data-start")) continue;
-              if (findTimedClipAncestor(target, rootComp)) continue;
+              if (hasAuthoredTimedAncestor(target)) continue;
               if (seen.has(target)) continue;
               seen.add(target);
               target.setAttribute("data-start", "0");
@@ -1102,7 +1100,7 @@ export function initSandboxRuntimeModular(): void {
           if (!(el instanceof HTMLElement)) continue;
           if (el === rootComp) continue;
           if (el.hasAttribute("data-start")) continue;
-          if (findTimedClipAncestor(el, rootComp)) continue;
+          if (hasAuthoredTimedAncestor(el)) continue;
           if (seen.has(el)) continue;
           if (el.tagName === "SCRIPT" || el.tagName === "STYLE" || el.tagName === "LINK") continue;
           seen.add(el);
@@ -1439,6 +1437,21 @@ export function initSandboxRuntimeModular(): void {
   };
 
   // fallow-ignore-next-line complexity
+  // Whether a timed clip participates in normal flow (static/relative/sticky).
+  // In-flow clips must leave the flow when hidden — `visibility:hidden` reserves
+  // their layout box, so a split sibling would stack below the active half
+  // instead of overlapping it. Positioned clips keep `visibility:hidden` (cheaper,
+  // and avoids disturbing absolute media playback). Computed once per element.
+  const timedClipInFlow = new WeakMap<Element, boolean>();
+  const isTimedClipInFlow = (el: HTMLElement): boolean => {
+    const cached = timedClipInFlow.get(el);
+    if (cached !== undefined) return cached;
+    const pos = window.getComputedStyle(el).position;
+    const inFlow = pos === "static" || pos === "relative" || pos === "sticky";
+    timedClipInFlow.set(el, inFlow);
+    return inFlow;
+  };
+
   const syncMediaForCurrentState = () => {
     const resolveMediaCompositionContext = (element: HTMLVideoElement | HTMLAudioElement) => {
       const compositionRoot = element.closest("[data-composition-id]");
@@ -1544,6 +1557,11 @@ export function initSandboxRuntimeModular(): void {
       if (rawNode instanceof HTMLVideoElement || rawNode instanceof HTMLImageElement) {
         colorGradingRuntime?.setSourceVisibility(rawNode, isVisibleNow);
       }
+      if (isVisibleNow) {
+        if (timedClipInFlow.get(rawNode)) rawNode.style.removeProperty("display");
+      } else if (isTimedClipInFlow(rawNode)) {
+        rawNode.style.display = "none";
+      }
     }
   };
 

diff --git a/packages/core/src/studio-api/helpers/sourceMutation.test.ts b/packages/core/src/studio-api/helpers/sourceMutation.test.ts
@@ -508,6 +508,28 @@ describe("splitElementInHtml", () => {
     expect(splitElementInHtml(source, { id: "box" }, 7.5, "box-split").matched).toBe(false);
   });
 
+  it("splits a GSAP element with no authored timing using fallback timing", () => {
+    // #title has no data-start/data-duration (GSAP-driven); the store supplies the range.
+    const gsapSource = `<html><body><div data-composition-id="root"><h1 id="title" class="title">Hi</h1></div></body></html>`;
+    const result = splitElementInHtml(gsapSource, { id: "title" }, 2, "title-split", {
+      start: 0,
+      duration: 6,
+    });
+    expect(result.matched).toBe(true);
+    // original windowed to [0, 2], clone to [2, 4] (attribute order is serializer-defined)
+    const original = result.html.match(/<h1[^>]*\bid="title"[^>]*>/)![0];
+    expect(original).toContain('data-start="0"');
+    expect(original).toContain('data-duration="2"');
+    const clone = result.html.match(/<h1[^>]*\bid="title-split"[^>]*>/)![0];
+    expect(clone).toContain('data-start="2"');
+    expect(clone).toContain('data-duration="4"');
+  });
+
+  it("still rejects a no-timing element when no fallback timing is given", () => {
+    const gsapSource = `<html><body><div data-composition-id="root"><h1 id="title">Hi</h1></div></body></html>`;
+    expect(splitElementInHtml(gsapSource, { id: "title" }, 2, "title-split").matched).toBe(false);
+  });
+
   it("adjusts media playback-start for the second half", () => {
     const mediaSource = source.replace(
       'id="box" class="clip" data-start="1" data-duration="6"',

diff --git a/packages/core/src/studio-api/helpers/sourceMutation.ts b/packages/core/src/studio-api/helpers/sourceMutation.ts
@@ -381,12 +381,23 @@ export function splitElementInHtml(
   target: SourceMutationTarget,
   splitTime: number,
   newId: string,
+  fallbackTiming?: { start: number; duration: number },
 ): SplitElementResult {
   const { document, wrappedFragment } = parseSourceDocument(source);
   const el = findTargetElement(document, target);
   if (!el || !isHTMLElement(el)) return { html: source, matched: false, newId: null };
 
-  const { start, duration, usesDataEnd } = resolveElementTiming(el);
+  const timing = resolveElementTiming(el);
+  const { usesDataEnd } = timing;
+  let { start, duration } = timing;
+  // GSAP-animated elements carry their timing in the script, not in data-* attrs,
+  // so the source has no authored duration. Fall back to the store's (GSAP-derived)
+  // range — the runtime windows visibility off data-start/data-duration regardless
+  // of class, so stamping both halves below makes each half show only in its window.
+  if (duration <= 0 && fallbackTiming && fallbackTiming.duration > 0) {
+    start = fallbackTiming.start;
+    duration = fallbackTiming.duration;
+  }
   if (duration <= 0 || splitTime <= start || splitTime >= start + duration) {
     return { html: source, matched: false, newId: null };
   }
@@ -405,6 +416,9 @@ export function splitElementInHtml(
   const clone = el.cloneNode(true) as HTMLElement;
   clone.setAttribute("id", newId);
   clone.removeAttribute("data-hf-id");
+  // Descendants carry their own data-hf-id; leaving them duplicates the id of
+  // every nested node (e.g. an inner <span>), so strip them on the clone too.
+  for (const node of clone.querySelectorAll("[data-hf-id]")) node.removeAttribute("data-hf-id");
   clone.setAttribute("data-start", String(Math.round(splitTime * 1000) / 1000));
   setElementDuration(clone, splitTime, secondDuration, usesDataEnd);
 
@@ -433,7 +447,9 @@ export function splitElementInHtml(
     duplicateCssRulesForId(document, originalId, newId);
   }
 
-  // Trim the original element's duration
+  // Trim the original element's duration. A GSAP element had no data-start; stamp
+  // it so the runtime windows the first half (visibility selects on [data-start]).
+  el.setAttribute("data-start", String(Math.round(start * 1000) / 1000));
   setElementDuration(el, start, firstDuration, usesDataEnd);
 
   // Insert clone after original

diff --git a/packages/core/src/studio-api/routes/files.ts b/packages/core/src/studio-api/routes/files.ts
@@ -24,6 +24,7 @@ import {
   type UnsafeMutationValue,
 } from "../helpers/finiteMutation.js";
 import type { GsapAnimation } from "../../parsers/gsapSerialize.js";
+import { classifyPropertyGroup } from "../../parsers/gsapConstants.js";
 import { parseGsapScriptAcorn } from "../../parsers/gsapParserAcorn.js";
 import { unrollComputedTimeline } from "../../parsers/gsapUnroll.js";
 import {
@@ -289,6 +290,18 @@ function stripStudioEditsFromTarget(document: Document, selector: string): numbe
   return stripped;
 }
 
+// A studio path-offset (--hf-studio-offset / data-hf-studio-path-offset) and a GSAP
+// position tween both drive translate — keeping both stacks the offsets (a gesture or
+// drag recorded over a stale offset plays shoved off-position). When a committed tween
+// writes a position property, the tween owns position, so the stale offset must go.
+function keyframesWritePosition(
+  keyframes: Array<{ properties: Record<string, number | string> }>,
+): boolean {
+  return keyframes.some((kf) =>
+    Object.keys(kf.properties).some((k) => classifyPropertyGroup(k) === "position"),
+  );
+}
+
 function lastKeyframeOpacity(kfs: GsapAnimation["keyframes"]): number | string | undefined {
   if (!kfs) return undefined;
   for (let i = kfs.keyframes.length - 1; i >= 0; i--) {
@@ -431,6 +444,24 @@ type GsapMutationRequest =
       cp1?: { x: number; y: number };
       cp2?: { x: number; y: number };
     }
+  | {
+      type: "update-motion-path-point";
+      animationId: string;
+      pointIndex: number;
+      x: number;
+      y: number;
+    }
+  | { type: "add-motion-path-point"; animationId: string; index: number; x: number; y: number }
+  | { type: "remove-motion-path-point"; animationId: string; index: number }
+  | {
+      type: "add-motion-path";
+      targetSelector: string;
+      position: number;
+      duration: number;
+      x: number;
+      y: number;
+      ease?: string;
+    }
   | { type: "remove-arc-path"; animationId: string }
   | {
       type: "add-with-keyframes";
@@ -498,6 +529,24 @@ type GsapMutationRequest =
 
 type GsapMutationResult = string | { script: string; skippedSelectors: string[] };
 
+// Mutations that can change a position tween's first keyframe (value/existence/timing)
+// and therefore require the pre-keyframe hold-`set`s to be re-synced afterwards.
+const HOLD_SYNC_MUTATION_TYPES = new Set<string>([
+  "add-keyframe",
+  "update-keyframe",
+  "remove-keyframe",
+  "remove-all-keyframes",
+  "add-with-keyframes",
+  "replace-with-keyframes",
+  "convert-to-keyframes",
+  "materialize-keyframes",
+  "update-motion-path-point",
+  "add-motion-path-point",
+  "remove-motion-path-point",
+  "delete",
+  "delete-all-for-selector",
+]);
+
 async function executeGsapMutation(
   body: GsapMutationRequest,
   block: NonNullable<ReturnType<typeof extractGsapScriptBlock>>,
@@ -517,6 +566,10 @@ async function executeGsapMutation(
     unrollDynamicAnimations,
     setArcPathInScript,
     updateArcSegmentInScript,
+    updateMotionPathPointInScript,
+    addMotionPathPointInScript,
+    removeMotionPathPointInScript,
+    addMotionPathToScript,
     removeArcPathFromScript,
     addAnimationWithKeyframesToScript,
     splitAnimationsInScript,
@@ -680,10 +733,39 @@ async function executeGsapMutation(
         ...(body.cp2 ? { cp2: body.cp2 } : {}),
       });
     }
+    case "update-motion-path-point": {
+      return updateMotionPathPointInScript(block.scriptText, body.animationId, body.pointIndex, {
+        x: body.x,
+        y: body.y,
+      });
+    }
+    case "add-motion-path-point": {
+      return addMotionPathPointInScript(block.scriptText, body.animationId, body.index, {
+        x: body.x,
+        y: body.y,
+      });
+    }
+    case "remove-motion-path-point": {
+      return removeMotionPathPointInScript(block.scriptText, body.animationId, body.index);
+    }
+    case "add-motion-path": {
+      const result = addMotionPathToScript(
+        block.scriptText,
+        body.targetSelector,
+        body.position,
+        body.duration,
+        { x: body.x, y: body.y },
+        body.ease,
+      );
+      return result.script;
+    }
     case "remove-arc-path": {
       return removeArcPathFromScript(block.scriptText, body.animationId);
     }
     case "add-with-keyframes": {
+      if (keyframesWritePosition(body.keyframes)) {
+        stripStudioEditsFromTarget(block.document, body.targetSelector);
+      }
       const result = addAnimationWithKeyframesToScript(
         block.scriptText,
         body.targetSelector,
@@ -695,6 +777,9 @@ async function executeGsapMutation(
       return result.script;
     }
     case "replace-with-keyframes": {
+      if (keyframesWritePosition(body.keyframes)) {
+        stripStudioEditsFromTarget(block.document, body.targetSelector);
+      }
       const script = removeAnimationFromScript(block.scriptText, body.animationId);
       const added = addAnimationWithKeyframesToScript(
         script,
@@ -970,11 +1055,18 @@ export function registerFileRoutes(api: Hono, adapter: StudioApiAdapter): void {
       target?: { id?: string; selector?: string; selectorIndex?: number };
       splitTime?: number;
       newId?: string;
+      elementStart?: number;
+      elementDuration?: number;
     }>(c);
     if ("error" in parsed) return parsed.error;
     if (typeof parsed.body.splitTime !== "number" || !parsed.body.newId) {
       return c.json({ error: "target, splitTime, and newId required" }, 400);
     }
+    const fallbackTiming =
+      typeof parsed.body.elementStart === "number" &&
+      typeof parsed.body.elementDuration === "number"
+        ? { start: parsed.body.elementStart, duration: parsed.body.elementDuration }
+        : undefined;
 
     let originalContent: string;
     try {
@@ -987,6 +1079,7 @@ export function registerFileRoutes(api: Hono, adapter: StudioApiAdapter): void {
       parsed.target,
       parsed.body.splitTime,
       parsed.body.newId,
+      fallbackTiming,
     );
     if (!result.matched) {
       return c.json({ ok: false, changed: false, content: originalContent, path: ctx.filePath });
@@ -1230,7 +1323,15 @@ export function registerFileRoutes(api: Hono, adapter: StudioApiAdapter): void {
     const result = await executeGsapMutation(body, block, respond);
     if (result instanceof Response) return result;
 
-    const newScript = typeof result === "string" ? result : result.script;
+    let newScript = typeof result === "string" ? result : result.script;
+    // Keep the "hold before first keyframe" sets in sync after any mutation that can
+    // change a position tween's first keyframe or its existence. Without it, an
+    // element snaps to its CSS base before the tween starts instead of holding its
+    // first keyframe (the universal NLE behavior).
+    if (HOLD_SYNC_MUTATION_TYPES.has(body.type)) {
+      const parser = await loadGsapParser();
+      newScript = parser.syncPositionHoldsBeforeKeyframes(newScript);
+    }
     const changed = newScript !== block.scriptText;
     const newHtml = changed ? block.replaceScript(newScript) : html;
     let backupPath: string | null = null;