mpg, .mp2, etc.).  The following are a list of input parameters
 and output variables.

 Input:
      filename:    must be the complete string of the movie filename
      FrameRange:  range of frames to examine
      NBackFrames: number of frames in static background, used only to
                   find fly in first frame
      opt1:        'neg' or 'pos'.  This multiplies the frame data by a
                   negative sign ('neg') or not ('pos').  FindFly needs the 
                   fly to be a bright 