Doesn't turn on camera by using OpenCV & arch linux - c++

Question

My develop H/W environment is Raspberry Pi2 & VX-1000 camera
My develop S/W environment is Arch linux & c++ & opencv
I could stream on webpage by using mjpg-streamer
with this command mjpg_streamer -i "./input_uvc.so -d /dev/video0 -n -f 30 -r 320x240" -o "./output_http.so -n -w ./www"
This run is good. (turns on camera (means turns on led on camera) )
But when I execute the program made by opencv code, it doesn't turn on camera (not turn on led) and the function cvCaptureFromCAM() returns NULL.
My source code is
#include <iostream>
#include <time.h>
#include <opencv/cv.h>
#include <opencv/highgui.h>
using namespace cv;
using namespace std;
int main(int argc,char** argv)
{
char c;
IplImage* frame;
CvCapture* capture;
capture = cvCaptureFromCAM(-1);
if(capture == NULL)
cout << "Strange!!" << endl;
cvSetCaptureProperty(capture, CV_CAP_PROP_FRAME_WIDTH , 320);
cvSetCaptureProperty(capture, CV_CAP_PROP_FRAME_HEIGHT , 240);
bool bLoop = true;
cout << "Start streaming" << endl;
while (bLoop){
cvGrabFrame(capture); // Get a frame from cam
frame = cvRetrieveFrame(capture, 0); // get a frame from capture
cvSaveImage("save.jpg", frame);
cvWaitKey(33); // wait key input for 33ms
}
cvReleaseCapture(&capture);
cvDestroyAllWindows();
return 0;
}

Answer 1

Let's change this line:
capture = cvCaptureFromCam(-1);
To:
capture = cvCaptureFromCam(0);
This will use the correct index that your video camera is in!

Answer 2

Try to pass 0 as the argument of cvCaptureFromCAM() or just simply listen to some connected camera by a loop:
CvCapture* capture = NULL;
for(int i = 0; i < 100 && capture == NULL; i++)
capture = cvCaptureFromCAM(i);
if(capture == NULL)
return;
Last but not least you should avoid the old C API, because it is deprecated and supported poorly, try to use cv::VideoCapture class instead.