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.
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.
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
VideoCapturehandles reading videos and grabbing frames from connected cameras. - The method
PROPERTY_NAMEhelps 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
getmethod to obtain frames per second.
