You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: feature_homography_track_demo.m
    path of file: ./repos/mexopencv/samples
    
    the code of the file until where you have to start completion: %% Feature homography based planar tracking
%
% Example of using features2d framework for interactive video homography
% matching. ORB features and FLANN matcher are used. The actual tracking is
% 
    
function feature_homography_track_demo(vid)
    % video file, and a default target to track [x,y,w,h]
    win = [];
    if nargin < 1
        vid = fullfile(mexopencv.root(), 'test', 'blais.mp4');
        assert(exist(vid, 'file') == 2, 'Missing video file');
        if true
            win = [135 165 285 175];  % face
        else
            win = [136 0 366 433];    % book
        end