From 13ea8349597bbcb874402d1771aea65766fd7ffc Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Miguel=20=C3=81ngel?= <miguel.sierra@heygen.com>
Date: Fri, 16 Oct 2026 23:16:13 +0000
Subject: [PATCH] perf(core): hold a clip at 0 inside a later scene until it is
 due (#5716)

---
 packages/core/src/runtime/entry.test.ts   | 15 +++++++++++++++
 packages/core/src/runtime/preloadMedia.ts | 10 ++++++----
 2 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/packages/core/src/runtime/entry.test.ts b/packages/core/src/runtime/entry.test.ts
index 5d0c54c257..d54f98505f 100644
--- a/packages/core/src/runtime/entry.test.ts
+++ b/packages/core/src/runtime/entry.test.ts
@@ -680,6 +680,21 @@ describe("runtime entry", () => {
       expect([first.preload, later.preload, untrimmed.preload]).toEqual(["", "none", ""]);
     });
 
+    it("defers a clip at 0 inside a later scene, by its start in the film", async () => {
+      servePreview();
+      const root = mountRoot();
+      const opening = timed(root, "div", "0");
+      const later = timed(root, "div", "5");
+      for (const scene of [opening, later]) {
+        scene.setAttribute("data-composition-id", "scene");
+        timed(scene, "div", "0");
+      }
+      await evaluateRuntime();
+      const [now, due] = [timed(opening, "video", "0"), timed(later, "video", "0")];
+      await Promise.resolve();
+      expect([now.preload, due.preload]).toEqual(["", "none"]);
+    });
+
     it("keeps a render loading every media element at bind", async () => {
       spyLoad();
       const [now, soon, later] = videos(mountRoot(), "0", "1.5", "5");
diff --git a/packages/core/src/runtime/preloadMedia.ts b/packages/core/src/runtime/preloadMedia.ts
index 2d98cd8798..43ac5ccf54 100644
--- a/packages/core/src/runtime/preloadMedia.ts
+++ b/packages/core/src/runtime/preloadMedia.ts
@@ -1,4 +1,5 @@
 import { parseStrictFiniteTimingNumber } from "./playbackRate";
+import { createRuntimeStartTimeResolver } from "./startResolver";
 import { skipsHiddenImages } from "./timedClipHide";
 
 type PreloadableMedia = Pick<
@@ -40,18 +41,19 @@ export function deferMediaUntilDue(): void {
   win.__hfMediaDeferral?.disconnect();
   win.__hfMediaDeferral = undefined;
   if (!skipsHiddenImages()) return;
-  const defer = (el: Element) => {
+  const defer = (el: Element, startInFilm: (el: Element) => number) => {
     const start = parseStrictFiniteTimingNumber(el.getAttribute("data-start"));
-    if (start != null && start > 0 && lengthIsAuthored(el))
+    if (start != null && lengthIsAuthored(el) && startInFilm(el) > 0)
       (el as HTMLMediaElement).preload = "none";
   };
   win.__hfMediaDeferral = new MutationObserver((records) => {
+    const startInFilm = createRuntimeStartTimeResolver({}).resolveMediaStartForElement;
     for (const record of records)
       for (const node of record.addedNodes) {
         if (node.nodeType !== 1) continue;
         const el = node as Element;
-        if (el.matches("video, audio")) defer(el);
-        for (const media of el.querySelectorAll("video, audio")) defer(media);
+        if (el.matches("video, audio")) defer(el, startInFilm);
+        for (const media of el.querySelectorAll("video, audio")) defer(media, startInFilm);
       }
   });
   win.__hfMediaDeferral.observe(document.documentElement, { childList: true, subtree: true });