OpenCV 计算fps(frames per second-fps)

在OpenCV中，类videoccapture处理摄像头读取视频和抓取帧。通过使用videoccapture中的get(PROPERTY_NAME)方法，你可以找到很多关于你正在播放的视频文件的信息。

如何在OpenCV中找到一个摄像头/网络摄像头的帧率?

在OpenCV中，查找连接的摄像头/网络摄像头的帧率不是直接的。文档说get(CAP_PROP_FPS)或get(CV_CAP_PROP_FPS)给出每秒的帧数。这对视频文件是正确的，但对网络摄像头不是。对于网络摄像头和许多其他连接摄像头，你必须手动计算每秒的帧数。您可以从视频中读取一定数量的帧，并查看计算每秒帧需要花费多少时间。

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 

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;
}

如何在OpenCV中找到视频的帧率?

如果你正在读取一个视频文件，你可以简单地使用get方法来获得每秒的帧数。下面的例子展示了使用方法
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; 

}