how to convert video inputed code to webcam inputed in matlab for tracking object

I have a code named "Object Tracking Using Adaptive Object Color Modeling" that works perfectly for object tracking using given video (mp4.avi etc). But now I want to convert this code to webcam any idea how?

%%initialize
obj = VideoReader('lar.avi');                            % Select Video File

tfn = get(obj,'numberOfFrames');                       % Total Frame Numbers

sf  = 1;                                               % Start Frame For Tracking

ef  = 400;                                             % End Frame For Tracking

Bin = 8;
img = read(obj,sf);                                    % Get First Frame

output = zeros(ef-sf+1,2);                             % Centroid Locations

% figure(); imshow(img)                                 % Show First Frame & Wait Till Select The Object
% or = round(getrect(figure(1)));                       % Coded Rect [xmin(col),ymin(row),width,height]
or  = [390,154,50,69];
CD  = round([or(2)+or(4)/2 or(1)+or(3)/2]);            % Object Centroid 
% close Figure 1