Find frame rate (frames per second-fps) in OpenCV (Python/C++)

In OpenCV the class VideoCapture handles reading videos and grabbing frames from connected cameras. There is a lot of information you can find about the video file you are playing by using the get(PROPERTY_NAME) method in VideoCapture. One of the common properties you may want to know is to find frame rate or frames per second. You can download all code and example images used in this post here.

This post has been tested on OpenCV 4.2.

How to find frame rate of a camera / webcam in OpenCV ?

In OpenCV finding the frame rate of a connected camera / webcam is not straight forward. The documentation says that get(CAP_PROP_FPS) or get(CV_CAP_PROP_FPS) gives the frames per second. Now that is true for video files, but not for webcams. For webcams and many other connected cameras, you have to calculate the frames per second manually. You can read a certain number of frames from the video and see how much time has elapsed to calculate frames per second.

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Click here to download the source code to this post

Python

#!/usr/bin/env python

import cv2
import time

if __name__ == '__main__' :

    # Start default camera
    video = cv2.VideoCapture(0);

    # Find OpenCV version
    (major_ver, minor_ver, subminor_ver) = (cv2.__version__).split('.')

    # With webcam get(CV_CAP_PROP_FPS) does not work.
    # Let's see for ourselves.

    if int(major_ver)  < 3 :
        fps = video.get(cv2.cv.CV_CAP_PROP_FPS)
        print("Frames per second using video.get(cv2.cv.CV_CAP_PROP_FPS): {0}".format(fps))
    else :
        fps = video.get(cv2.CAP_PROP_FPS)
        print("Frames per second using video.get(cv2.CAP_PROP_FPS) : {0}".format(fps))

    # Number of frames to capture
    num_frames = 120;

    print("Capturing {0} frames".format(num_frames))

    # Start time
    start = time.time()

    # Grab a few frames
    for i in range(0, num_frames) :
        ret, frame = video.read()

    # End time
    end = time.time()

    # Time elapsed
    seconds = end - start
    print ("Time taken : {0} seconds".format(seconds))

    # Calculate frames per second
    fps  = num_frames / seconds
    print("Estimated frames per second : {0}".format(fps))

    # Release video
    video.release()

C++

#include "opencv2/opencv.hpp"
#include <time.h>

using namespace cv;
using namespace std;

int main(int argc, char** argv)
{

    // Start default camera
    VideoCapture video(0);

    // With webcam get(CV_CAP_PROP_FPS) does not work.
    // Let's see for ourselves.

    // double fps = video.get(CV_CAP_PROP_FPS);
    // If you do not care about backward compatibility
    // You can use the following instead for OpenCV 3
    double fps = video.get(CAP_PROP_FPS);
    cout << "Frames per second using video.get(CAP_PROP_FPS) : " << fps << endl;

    // Number of frames to capture
    int num_frames = 120;

    // Start and end times
    time_t start, end;

    // Variable for storing video frames
    Mat frame;

    cout << "Capturing " << num_frames << " frames" << endl ;

    // Start time
    time(&start);

    // Grab a few frames
    for(int i = 0; i < num_frames; i++)
    {
        video >> frame;
    }

    // End Time
    time(&end);

    // Time elapsed
    double seconds = difftime (end, start);
    cout << "Time taken : " << seconds << " seconds" << endl;

    // Calculate frames per second
    fps  = num_frames / seconds;
    cout << "Estimated frames per second : " << fps << endl;

    // Release video
    video.release();
    return 0;
}

How to find frame rate of a video in OpenCV ?

If you are reading a video file you can simply use the get method to obtain frames per second. The following examples show the usage.

Python

import cv2
if __name__ == '__main__' :

    video = cv2.VideoCapture("video.mp4");

    # Find OpenCV version
    (major_ver, minor_ver, subminor_ver) = (cv2.__version__).split('.')

    if int(major_ver)  < 3 :
        fps = video.get(cv2.cv.CV_CAP_PROP_FPS)
        print ("Frames per second using video.get(cv2.cv.CV_CAP_PROP_FPS): {0}".format(fps))
    else :
        fps = video.get(cv2.CAP_PROP_FPS)
        print ("Frames per second using video.get(cv2.CAP_PROP_FPS) : {0}".format(fps))

   video.release()

C++

#include "opencv2/opencv.hpp"

using namespace cv;
using namespace std;

int main(int argc, char** argv)
{

    // Open video file
    VideoCapture video("video.mp4");

    // double fps = video.get(CV_CAP_PROP_FPS);

    // For OpenCV 3, you can also use the following
    double fps = video.get(CAP_PROP_FPS);

    cout << "Frames per second using video.get(CAP_PROP_FPS) : " << fps << endl;

    video.release();
    return 0; 

}

Summary

In this we discussed finding the frames per second-fps in OpenCV. We also provided the Python/C++ code for practice and study.

Key Takeaways

OpenCV class VideoCapture handles reading videos and grabbing frames from connected cameras.
The method PROPERTY_NAME helps find lot of information about the video file being played.
Common property we may want to know, frame rate or frames per second, is discussed in detail.
When reading a video file simply use the get method to obtain frames per second.