1 files changed, 5 insertions, 4 deletions
diff --git a/apps/web/src/timeline/index.ts b/apps/web/src/timeline/index.ts
index 3775e006..21944561 100644
--- a/apps/web/src/timeline/index.ts
+++ b/apps/web/src/timeline/index.ts
@@ -1,4 +1,4 @@
-import { type MediaTime, ZERO_MEDIA_TIME } from "@/wasm";
+import { addMediaTime, type MediaTime, ZERO_MEDIA_TIME } from "@/wasm";
 import type { SceneTracks } from "./types";
 
 export * from "./types";
@@ -22,9 +22,10 @@ export function calculateTotalDuration({
 	let maxEnd: MediaTime = ZERO_MEDIA_TIME;
 	for (const track of orderedTracks) {
 		for (const element of track.elements) {
-			// `startTime + duration` is integer-by-construction (both `MediaTime`),
-			// so the cast re-establishes the brand without runtime work.
-			const elementEnd = (element.startTime + element.duration) as MediaTime;
+			const elementEnd = addMediaTime({
+				a: element.startTime,
+				b: element.duration,
+			});
 			if (elementEnd > maxEnd) maxEnd = elementEnd;
 		}
 	}