Update

app.py

@@ -485,6 +485,8 @@ def add_tracking_points(
     tracking_points, first_frame_path, last_frame_path, evt: gr.SelectData
 ):  # SelectData is a subclass of EventData
     print(f"You selected {evt.value} at {evt.index} from {evt.target}")
+    if not tracking_points:
+        tracking_points = [[]]
     tracking_points[-1].append(evt.index)
 
     transparent_background = Image.open(first_frame_path).convert("RGBA")