fix(web): notify subscribers when late fallbackDuration updates playback store

apps/web/__tests__/unit/playback-store.test.ts

@@ -80,4 +80,40 @@ describe("playback store", () => {
 		video.dispatchEvent(new Event("timeupdate"));
 		expect(subscriber).toHaveBeenCalledTimes(1);
 	});
+
+	it("notifies subscribers when late fallbackDuration changes the store duration", () => {
+		const store = createPlaybackStore(0);
+		let observedDuration = store.getDuration();
+		store.subscribe(() => {
+			observedDuration = store.getDuration();
+		});
+
+		expect(observedDuration).toBe(0);
+
+		store.setFallbackDuration(60);
+
+		expect(observedDuration).toBe(60);
+		expect(store.getDuration()).toBe(60);
+	});
+
+	it("does not notify subscribers when fallbackDuration does not change total duration", () => {
+		const video = Object.assign(new EventTarget(), {
+			currentTime: 0,
+			duration: 120,
+			paused: true,
+			ended: false,
+		});
+		const store = createPlaybackStore(60);
+		store.attach(video as unknown as HTMLVideoElement);
+
+		const subscriber = vi.fn(() => store.getDuration());
+		store.subscribe(subscriber);
+		subscriber.mockClear();
+
+		store.setFallbackDuration(90);
+
+		expect(subscriber).not.toHaveBeenCalled();
+		expect(store.getDuration()).toBe(120);
+		store.detach();
+	});
 });

apps/web/app/s/[videoId]/_components/playback/playback-store.ts

@@ -175,8 +175,12 @@ export function createPlaybackStore(fallbackDuration: number | null = 0) {
 	const getPlaying = () => playing;
 
 	const setFallbackDuration = (next: number | null) => {
+		const previousDuration = getDuration();
 		fallback = normalizeDuration(next);
 		if (!isFiniteDuration(duration)) duration = fallback;
+		if (getDuration() !== previousDuration) {
+			emitTime();
+		}
 	};
 
 	const seek = (target: number) => {