MultiTracker's trackers initialization for first frame

I followed the [example mentioned in link of Opencv 3.1](http://docs.opencv.org/3.1.0/d5/d07/tutorial_multitracker.html) How to initialize the trackers for the first frame ??? i mean in the example in the link they have used selectRoi for selection of objects befor the for loop. How to do the same with HOG SVM ??? someone plz help