Fixes in OpenCV and RTSP

We've finally got it going!

I'll get onto what was wrong in a second but first I want to share this line with you:

    CvCapture *camera = cvCreateFileCapture("rtsp://admin:admin@192.168.1.128/ch1-s1?tcp"); 

As you can see it is the same as my camera connection url in the previous post except I've added ?tcp to the end. I've found that this forces the rtsp connection to run using the tcp protocol instead of the udp protocol which is useful if you can't afford to have any packet loss. This gives us a decent picture but still performed very poorly, freezing often and dropping the frame rate down to something terrible.



I also found with this that occasionally the connection would be dropped and the code I had before would have no way of recovering so would just exit. Hence I present to you the revised code which upon receiving NULL when trying to get an image takes this as the connection being down and re-establishes it.

/* 
 * File:   main.cpp
 * Author: Ryan
 *
 * Created on October 27, 2011, 2:23 PM
 */

#include <cstdlib>
#include "opencv2/core/core.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/contrib/contrib.hpp"
#include "opencv2/features2d/features2d.hpp"
#include "opencv2/legacy/legacy.hpp"
#include "opencv2/video/tracking.hpp"
#include <stdio.h> 

using namespace std;
using namespace cv;

int main() {

    //        CvCapture *camera = cvCreateFileCapture("/home/ryan/NetBeansProjects/OpenRTSP/video-H264-1");
    //        CvCapture *camera = cvCreateFileCapture("stream_fifo");    
    //        CvCapture *camera = cvCreateFileCapture("Wildlife.wmv");
    CvCapture *camera = cvCreateFileCapture("rtsp://admin:admin@192.168.1.128/ch1-s1?tcp"); //purple cam /?tcp
    //        CvCapture *camera=cvCreateFileCapture("http://192.168.1.5/image.jpg"); //black cam
    //    CvCapture *camera = cvCreateCameraCapture(0); //built in cam
    //    cvWaitKey(10000);
    if (camera == NULL) {
        printf("camera is null, aborting...");
        return -1;
    }
    printf("camera is not null\n");
    fflush(stdout);
    cvNamedWindow("img");
    int i = 0;
    while (cvWaitKey(10) != 27) {
        //         CvCapture *camera=cvCreateFileCapture("http://192.168.1.5/image.jpg");
        IplImage *img = cvQueryFrame(camera);
        if (img == NULL) {
            printf("img == null ");
            fflush(stdout);
            camera = cvCreateFileCapture("rtsp://admin:admin@192.168.1.128/ch1-s1?tcp");
        }
        cvShowImage("img", img);
        //        cvReleaseCapture(&camera); 
        //        printf("Image: %i\n", ++i);
    }
    cvReleaseCapture(&camera);
    return 0;
}

This code also has the new forced tcp urls in it although they are no longer needed since we have got to the root of the problem.

It turns out that our camera has a small buffer inside it which it uses to store the images it has captured for retrieval. If you don't retrieve the images at a fast enough rate then it is possible to try and retrieve one that is partially over-written or in the process of being written to by the camera's firmware. At least this is the theory my colleague came up with and I am inclined to agree (damn him for figuring it out before me!).

So the fix is pretty simple in this project and is already in the code above; we simply reduce the length of time between image retrieval from the camera by reducing the length of time the program waits for a key press in the loop. If you can see it the line of code is:

    while (cvWaitKey(10) != 27) {

which has been changed from:

    while (cvWaitKey(100) != 27) {

Simple eh! Well at least it is for this small test program. Our main program is considerably bigger with some pretty demanding routines so insuring fast image retrieval may not be such an easy task.

For now however, this is definitely being marked a success!