Why the frames pass too quikly

I run the foreground detector and blob analysis command but output video frames pass too quickly

 videoSource = vision.VideoFileReader('abc.avi',...
    'ImageColorSpace','Intensity','VideoOutputDataType','uint8');

 detector = vision.ForegroundDetector('NumTrainingFrames', 75, ...
    'InitialVariance', 100*100);

 blob = vision.BlobAnalysis('CentroidOutputPort', false, 'AreaOutputPort',...
    false, 'BoundingBoxOutputPort', true, 'MinimumBlobAreaSource','Property',...
    'MinimumBlobArea', 30);

 shapeInserter = vision.ShapeInserter('BorderColor', 'White');

 VideoPlayer = vision.VideoPlayer();

 while ~isDone(videoSource)
    frame = step(videoSource);
    fgMask = step(detector, frame);
    bbox = step(blob, fgMask);
    out = step(shapeInserter, frame, bbox);
    step(VideoPlayer, out);
end

 release(VideoPlayer);
release(videoSource);