pass 0 instead of None

pandora/item/models.py

@@ -1135,7 +1135,7 @@ class Item(models.Model):
         offset = 0
         streams = self.streams()
         for stream in streams:
-            if stream.duration + offset < float(position):
+            if stream.duration + offset < position:
                 offset += stream.duration
             else:
                 if not stream.file.is_video or not stream.file.info.get('video'):

pandora/item/views.py

@@ -777,6 +777,8 @@ def frame(request, id, size, position=None):
                 position = frames[int(position)]['position']
             elif item.poster_frame == -1 and item.sort.duration:
                 position = item.sort.duration/2
+            else:
+                position = 0
         else:
             position = item.poster_frame
     else: