Implement safety fallback for duration display.

frontend/components/VideoListItem.tsx

@@ -34,7 +34,11 @@ export default function VideoListItem({
 }) {
   let displayDuration = null;
   if (duration !== null) {
-    displayDuration = duration;
+    if (typeof duration === 'string') {
+      displayDuration = parseFloat(duration);
+    } else {
+      displayDuration = duration;
+    }
   } else if (
     sourceVideoStart !== null
     && sourceVideoEnd !== null