Matlab - Error al usar vision.VideoPlayer

%% detectAndTrackFaces

% Automatically detects and tracks multiple faces in a webcam-acquired

% video stream.

%

% Copyright 2013-2014 The MathWorks, Inc 

clear classes;

%% Instantiate video device, face detector, and KLT object tracker

vidObj = webcam;

faceDetector = vision.CascadeObjectDetector(); % Finds faces by default

tracker = MultiObjectTrackerKLT;

%% Get a frame for frame-size information

frame = snapshot(vidObj);

frameSize = size(frame);

%% Create a video player instance

videoPlayer  = vision.VideoPlayer('Position',[200 100 fliplr(frameSize(1:2)+30)]);

%% Iterate until we have successfully detected a face

bboxes = [];

while isempty(bboxes)

    framergb = snapshot(vidObj);

    frame = rgb2gray(framergb);

    bboxes = faceDetector.step(frame);

end

tracker.addDetections(frame, bboxes);

%% And loop until the player is closed

frameNumber = 0;

keepRunning = true;

disp('Press Ctrl-C to exit...');

while keepRunning

    framergb = snapshot(vidObj);

    frame = rgb2gray(framergb);

    if mod(frameNumber, 10) == 0

        % (Re)detect faces.

        %

        % NOTE: face detection is more expensive than imresize; we can

        % speed up the implementation by reacquiring faces using a

        % downsampled frame:

        % bboxes = faceDetector.step(frame);

        bboxes = 2 * faceDetector.step(imresize(frame, 0.5));

        if ~isempty(bboxes)

            tracker.addDetections(frame, bboxes);

        end

    else

        % Track faces

        tracker.track(frame);

    end

    % Display bounding boxes and tracked points.

    displayFrame = insertObjectAnnotation(framergb, 'rectangle',...

        tracker.Bboxes, tracker.BoxIds);

    displayFrame = insertMarker(displayFrame, tracker.Points);

    videoPlayer.step(displayFrame);

    frameNumber = frameNumber + 1;

end

%% Clean up

release(videoPlayer);