While tracking face in a video Iam using these instructions but the face is not getting tracked properly.Also I am not getting why the position in line 3 is kept [300 300 videoInfo. VideoSize]

tracker = vision.HistogramBasedTracker;

% Initialize the tracker histogram using the Hue channel pixels from the % nose. initializeObject(tracker, hueChannel, noseBBox(1,:));

% Create a video player object for displaying video frames. videoPlayer = vision.VideoPlayer('Position',[300 300 videoInfo.VideoSize]);