Fix bug when using file as input source

sksurgerydavinci/ui/sksurgerydavinci_demo.py

@@ -34,7 +34,15 @@ def run_demo(args):
     num_of_input_sources = len(video_sources)
 
     if num_of_input_sources == 1:
-        viewer = MonoViewer(int(video_sources[0]))
+
+        if len(video_sources[0]) > 1:
+            # it is a filename
+            source = video_sources[0]
+            print(f"Loading video from {source}")
+        else:
+            source = int(video_sources[0])
+
+        viewer = MonoViewer(source)
 
     elif int(video_sources[1]) == -1:
         viewer = MockStereoViewer(int(video_sources[0]))