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I can't seem to figure out what is wrong with the code fragment I have...it keeps on outputting over 200 fps for some reason. I tested with OpenCV and the unprocessed video is about 30 fps.

int n_frame = 0;
Mat previous;
auto start = chrono::high_resolution_clock::now();
while (m_cap.isOpened()) {
    if (n_frame % 100 == 1) {
        auto end = chrono::high_resolution_clock::now();    
        auto time = chrono::duration_cast<chrono::seconds>(end - start);
        cout << "the fps is: " << 1.0 / (static_cast<double>(time.count()) / n_frame) << endl;
        //cin.ignore(1000, '\n');
    }
    n_frame++;
    cout << "frame number: " << n_frame << endl;
    Mat frame, original;

    m_cap >> frame;
    if (frame.empty())
        break;


//do some video processing down here eg thresholding
}
Howard Wang
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  • 18

1 Answers1

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I think you forgot to re-initialize the start time, here is modified code, this provides consistent fps value, I tested in my laptop and got around 33.2, I just count up to 100 frames and reinitialize everything, this seems to work 

int n_frame = 0;
Mat previous;
auto start = std::chrono::high_resolution_clock::now();
VideoCapture m_cap(0);

while (m_cap.isOpened()) {
    n_frame++;
    if (n_frame == 100) {
        auto end = std::chrono::high_resolution_clock::now();
        auto time = std::chrono::duration_cast<chrono::seconds>(end - start);
        cout << "the fps is: " << (n_frame / static_cast<double>(time.count())) << endl;
        start = end;
        n_frame = 0;
    }
    //cout << "frame number: " << n_frame << endl;
    Mat frame, original;
    m_cap >> frame;
    if (frame.empty())
        break;
}
GOPI
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  • 2
  • Thanks, that seemed to have fixed it...although it's at around 18 now...guess I need to see what's slowing the processing down so much – Howard Wang Jan 18 '18 at 04:04