all video processing samples use camera as default source (and fallback to synth in case of capture error)

samples/python2/camshift.py

@@ -98,7 +98,7 @@ class App(object):
 if __name__ == '__main__':
     import sys
     try: video_src = sys.argv[1]
-    except: video_src = video.presets['chess']
+    except: video_src = 0
     print help_message
     App(video_src).run()