OpenCV VideoCapture set function does not change frame rate FPS? - opencv

Question

Good afternoon everybody,
In OpenCV I'm having trouble getting the VideoCapture's set function to change the frame rate. Here is my test program, using the "768x576.avi" test video file from the "C:\OpenCV-3.1.0\opencv\sources\samples\data" directory
// VideoCaptureSetTest.cpp
#include<opencv2/core/core.hpp>
#include<opencv2/highgui/highgui.hpp>
#include<opencv2/imgproc/imgproc.hpp>
#include<iostream>
#include<conio.h> // it may be necessary to change or remove this line if not using Windows
///////////////////////////////////////////////////////////////////////////////////////////////////
int main() {
cv::VideoCapture capVideo;
cv::Mat imgFrame;
capVideo.open("768x576.avi");
if (!capVideo.isOpened()) { // if unable to open video file
std::cout << "error reading video file" << std::endl << std::endl; // show error message
_getch(); // it may be necessary to change or remove this line if not using Windows
return(0); // and exit program
}
char chCheckForEscKey = 0;
double dblFPS = capVideo.get(CV_CAP_PROP_FPS);
std::cout << "1st time - dblFPS = " << dblFPS << "\n"; // this prints "10" to std out as expected
bool blnSetReturnValue = capVideo.set(CV_CAP_PROP_FPS, 5);
std::cout << "2nd time - dblFPS = " << dblFPS << "\n"; // this also prints "10", why not "5" as expected ??!!
std::cout << "blnSetReturnValue = " << blnSetReturnValue << std::endl; // this prints "0" (i.e. false)
while (chCheckForEscKey != 27) {
capVideo.read(imgFrame);
if (imgFrame.empty()) break;
cv::imshow("imgFrame", imgFrame);
chCheckForEscKey = cv::waitKey(1);
}
return(0);
}
I'm using a very standard setup here, OpenCV 3.1.0, Visual Studio 2015, Windows 10, and the .avi file I'm testing with is the one that ships with OpenCV.
No matter what I attempt to set the FPS to, it stays at 10 and the set function always returns false.
Yes, I'm aware of the hack fix of setting the cv::waitKey() parameter to a larger value to achieve a certain delay, but this would then be computer-dependent and I may need to run video on various computers in the future so this is not an option.
Am I doing something wrong? Is the VideoCapture::set function known to not work in some cases? Has anybody else experienced the same results? I checked the OpenCV issue tracker and did not find anything to this effect. Is this a bug I should raise a ticket for? Anybody else with some experience with this please advise.