--- a/python/cvutils.py	Wed Jul 18 02:54:02 2012 -0400
+++ b/python/cvutils.py	Wed Jul 18 02:54:22 2012 -0400
@@ -129,7 +129,7 @@
                         images.append(img)
         return images
 
-    def displayTrajectories(videoFilename, objects, homography = None, firstFrameNum = 0):
+    def displayTrajectories(videoFilename, objects, homography = None, firstFrameNum = 0, lastFrameNumArg = None):
         '''Displays the objects overlaid frame by frame over the video '''
         capture = cv2.VideoCapture(videoFilename)
         if capture.isOpened():
@@ -137,7 +137,12 @@
             ret = True
             frameNum = firstFrameNum
             capture.set(cv2.cv.CV_CAP_PROP_POS_FRAMES, firstFrameNum)
-            while ret and key!= 113: # 'q'
+            if not lastFrameNumArg:
+                from sys import maxint
+                lastFrameNum = maxint
+            else:
+                lastFrameNum = lastFrameNumArg
+            while ret and key!= 113 and frameNum < lastFrameNum: # 'q'
                 ret, img = capture.read()
                 if ret:
                     print('frame {0}'.format(frameNum))