Optical Flow in Computer Vision tool box

In the vision.optical flow, How can I plot the vector direction. Quiver draw the vector into image and i have video player. It also requires block size. Here is the code that i have (it is the same one in the example):

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hvfr = vision.VideoFileReader('MyVid.mov', ...
    'ImageColorSpace', 'Intensity', ...
    'VideoOutputDataType', 'uint8');
hidtc = vision.ImageDataTypeConverter;
hof = vision.OpticalFlow('ReferenceFrameDelay', 2);
hof.OutputValue = 'Horizontal and vertical components in complex form';
hmean1 = vision.Mean;
hsi = vision.ShapeInserter('Shape','Lines','BorderColor','Custom', 'CustomBorderColor', 255);
hvp = vision.VideoPlayer('Name', 'Motion Vector');
ii=0;

while ~isDone(hvfr)&&ii<1000

      frame = step(hvfr);
      im = step(hidtc, frame); 
      of = step(hof, im);      

      lines = videooptflowlines(of, 20); % generate coordinate points
      if ~isempty(lines)

          out =  step(hsi, im, lines); % draw lines to indicate flow

step(hvp, out);%show it on the video player

      end

      ii=ii+1;
  end

release(hvp);
release(hvfr);

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Thanks