From ad87313ee2f04b598d88111e1dc0ee4f1bc33ce3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Miguel=20=C3=81ngel?= <miguel.sierra@heygen.com>
Date: Fri, 25 Sep 2026 04:43:49 +0000
Subject: [PATCH] fix(core): a Lottie animation in a mounted composition plays
 from that composition's start (#4471)

---
 .../core/src/runtime/adapters/lottie.test.ts  | 32 +++++++++++++++++++
 packages/core/src/runtime/adapters/lottie.ts  | 19 +++++++++--
 packages/core/src/runtime/init.ts             |  4 ++-
 3 files changed, 52 insertions(+), 3 deletions(-)

diff --git a/packages/core/src/runtime/adapters/lottie.test.ts b/packages/core/src/runtime/adapters/lottie.test.ts
index 880377bef9..3697c060fd 100644
--- a/packages/core/src/runtime/adapters/lottie.test.ts
+++ b/packages/core/src/runtime/adapters/lottie.test.ts
@@ -1,5 +1,6 @@
 import { describe, it, expect, vi, beforeEach, afterEach } from "vitest";
 import { createLottieAdapter } from "./lottie";
+import { createRuntimeStartTimeResolver } from "../startResolver";
 
 const lottieWindow = window as Window & {
   lottie?: {
@@ -84,6 +85,37 @@ describe("lottie adapter", () => {
   });
 
   describe("seek", () => {
+    function mountedAt(start: string) {
+      document.body.innerHTML = `<div data-composition-id="root"><div data-composition-id="host" data-start="${start}"><div data-composition-id="walk"><div id="player"></div></div></div></div>`;
+      const { resolveStartForElement } = createRuntimeStartTimeResolver({});
+      const adapter = createLottieAdapter({
+        resolveStartSeconds: (el) => resolveStartForElement(el, 0),
+      });
+      return { adapter, player: document.getElementById("player")! };
+    }
+
+    it("seeks a player in a mounted composition to the time since that composition started", () => {
+      const { adapter, player } = mountedAt("3");
+      const anim = { ...createLottieWebAnim(), wrapper: player };
+      const dot = { ...createDotLottiePlayer({ totalFrames: 60, frameRate: 30 }), canvas: player };
+      lottieWindow.__hfLottie = [anim, dot];
+      adapter.seek({ time: 4 });
+      expect(anim.goToAndStop).toHaveBeenCalledWith(1000, false);
+      expect(dot.setCurrentRawFrameValue).toHaveBeenCalledWith(30);
+      adapter.seek({ time: 1 });
+      expect(anim.goToAndStop).toHaveBeenLastCalledWith(0, false);
+      document.body.innerHTML = "";
+    });
+
+    it("keeps page time for a player in a composition that starts at 0", () => {
+      const { adapter, player } = mountedAt("0");
+      const anim = { ...createLottieWebAnim(), wrapper: player };
+      lottieWindow.__hfLottie = [anim];
+      adapter.seek({ time: 2 });
+      expect(anim.goToAndStop).toHaveBeenCalledWith(2000, false);
+      document.body.innerHTML = "";
+    });
+
     it("seeks lottie-web with goToAndStop in ms", () => {
       const anim = createLottieWebAnim();
       lottieWindow.__hfLottie = [anim];
diff --git a/packages/core/src/runtime/adapters/lottie.ts b/packages/core/src/runtime/adapters/lottie.ts
index f1edf2490a..3f7c3c2d8c 100644
--- a/packages/core/src/runtime/adapters/lottie.ts
+++ b/packages/core/src/runtime/adapters/lottie.ts
@@ -49,7 +49,19 @@ import { swallow } from "../diagnostics";
  * via the global `lottie` object, so compositions that call
  * `lottie.loadAnimation(...)` without manually registering still work.
  */
-export function createLottieAdapter(): RuntimeDeterministicAdapter {
+export function createLottieAdapter(params?: {
+  resolveStartSeconds?: (element: Element) => number;
+}): RuntimeDeterministicAdapter {
+  const secondsIntoComposition = (anim: unknown, pageTime: number): number => {
+    const el = isLottieWebAnimation(anim) ? anim.wrapper : (anim as DotLottiePlayer).canvas;
+    const composition =
+      el && typeof (el as Element).closest === "function"
+        ? (el as Element).closest("[data-composition-id]")
+        : null;
+    if (!composition || !params?.resolveStartSeconds) return pageTime;
+    return Math.max(0, pageTime - params.resolveStartSeconds(composition));
+  };
+
   return {
     name: "lottie",
 
@@ -78,12 +90,13 @@ export function createLottieAdapter(): RuntimeDeterministicAdapter {
     },
 
     seek: (ctx) => {
-      const time = Math.max(0, Number(ctx.time) || 0);
+      const pageTime = Math.max(0, Number(ctx.time) || 0);
       const instances = (window as LottieWindow).__hfLottie;
       if (!instances || instances.length === 0) return;
 
       for (const anim of instances) {
         try {
+          const time = secondsIntoComposition(anim, pageTime);
           const loops = anim.loop === true;
           if (isLottieWebAnimation(anim)) {
             // lottie-web: AnimationItem
@@ -245,6 +258,7 @@ interface LottieWebAnimation {
   totalFrames: number;
   frameRate: number;
   loop?: boolean | number;
+  wrapper?: unknown;
 }
 
 interface LottieWebGlobal {
@@ -261,6 +275,7 @@ interface DotLottiePlayer {
   frameRate?: number;
   duration?: number;
   loop?: boolean;
+  canvas?: unknown;
 }
 
 interface LottieWindow extends Window {
diff --git a/packages/core/src/runtime/init.ts b/packages/core/src/runtime/init.ts
index 2dfef746c7..1de8bd4859 100644
--- a/packages/core/src/runtime/init.ts
+++ b/packages/core/src/runtime/init.ts
@@ -3269,7 +3269,9 @@ export function initSandboxRuntimeModular(): void {
       resolveStartSeconds: (element) => resolveStartForElement(element, 0),
     }),
     createAnimeJsAdapter(),
-    createLottieAdapter(),
+    createLottieAdapter({
+      resolveStartSeconds: (element) => resolveStartForElement(element, 0),
+    }),
     createThreeAdapter(),
     createMapboxAdapter(),
     createLeafletAdapter(),