How to plot boundary on video frames called inside step() function

I am calling some images inside for loop and then doing some processing on those images. After that i am using a step function to display those frames/masks inside a video player. How can i add a boundary to an object inside that frame/mask. Below is the rough sketch of the code.

 videoPlayer = vision.VideoPlayer();
 maskPlayer = vision.VideoPlayer();
    for ii = 1:nfiles
      filenameii = [............]
      frame= imread(filenameii);
      mask = dOB(frame,BackgroundImg);
    % some processing on the images

      mask= bwareaopen(mask,27);
      boundaries = bwboundaries(mask,'noholes');
      B=boundaries{1};
      Centroid = regionprops(mask,'centroid');
      Centroids = cat(1, Centroid.Centroid);

      plot(B(:,2),B(:,1),'g','LineWidth',3);
      plot(Centroids(:,1), Centroids(:,2), 'r+', 'MarkerSize', 10);
      step(videoPlayer,frame);
      step(maskPlayer, mask); 
  end

I want the boundary B to be plotted on the mask image that i am calling inside step function.

P.S: I know how to display it on a figure using hold on and i am using MATLAB. Any guidance will be appreciated.