How to measure FPS of an OpenCV camera preview?

Android/Java
9

Alright all, so I’ve worked on a new piece of code that was originally written in Python, but i had translated to Java. So, the code shows up with zero errors, however… the framerate has still not been printed! I’ve been traversing the internet for a reason as to why this is the case. Could anybody explain to me as to why

import org.opencv.core.Mat;
import org.opencv.videoio.VideoCapture;

import java.time.OffsetDateTime;
import java.time.temporal.ChronoUnit;

    public static void main (String[] args) {
        //Pass your video capture argument
        VideoCapture cap = new VideoCapture(0);
        printFps(cap);
    }

    // Takes an OpenCV VideoCapture as an argument.
    public static void printFps(VideoCapture capture) {
        // Completely arbitrary number of frames but 120 is a decent sample.
        int num_frames = 120;

        // Declare variables for timekeeping.
        // time1 = where the sample start time will be stored
        // time2 = where the sample end time will be stored
        OffsetDateTime time1, time2;

        // Create a new Matrix (OpenCV's variable for storing a video frame)
        Mat frame = new Mat();

        // Print out a message indicating frames are
        // starting to be captured now.
        System.out.println("Capturing frames now.");

        // Save the current time in the first variable.
        time1 = OffsetDateTime.now();

        // Capture a number of frames
        for (int index = 0; index < num_frames; ++index) {
            // Store the frame in the frame variable
            capture.read(frame);
        }

        // When this operation finishes, store the current time in the second variable.
        time2 = OffsetDateTime.now();

        // Calculate the time that passed during the captures
        long secondsBetween = ChronoUnit.SECONDS.between(time2, time1);

        // Calculate frames per second
        int fps = num_frames / (int) secondsBetween;
        Log.i(TAG, "Estimated FPS: " + fps);

        // Release the VideoCapture object
        capture.release();
    }

EDIT: added code to call the printFps function