How to detect the number of people in a video using boofcv?

Question

I use this great project https://github.com/lessthanoptimal/BoofCV/tree/v0.23/examples/src/boofcv/examples

Trying to detect number of people in a video. Currently it works great for me to track an object if I know the predetermined initial location

Quadrilateral_F64 location = new Quadrilateral_F64(
                411.0,  262.0,
                526.0,  253.0,
                535.0,  358.0,
                415.0,  349.0);
        ImageBase frame = video.next();
        tracker.initialize(frame,location);
........
        // Track the object across each video frame and display the results
        long previous = 0;
        while( video.hasNext() ) {
            frame = video.next();

            boolean visible = tracker.process(frame,location); 

For detecting the number of people, do I need to use a silhouette? or what is the correct implementation? I tried with Quadrilateral_F64 but it has four square coordinates.

GOAL: to feed a video, and on the output print the "number of people" to console: 1 or 2 or 10

Am I in the right API Quadrilateral_F64?