Trouble with openCV getting a stream using a Hikvision camera

C++
1

I’m using a Hikvision camera with openCV with the purpose of getting a streaming of the camera in a window on my pc. I started using a SDK from HIKVISION (here is the link: https://www.hikvision.com/es/support/download/sdk/device-network-sdk--for-linux-64-bit-/) for getting some examples and start practicing. I used the psdatacall_demo because it was the most similar demo to my objective. This file records a video and saves it in a .dat format.

Below I paste the SDK function where the script saves the buffer in the .dat file. My goal is to change this approach to a real-time display window of the camera video using the OpenCV library.

void PsDataCallBack(LONG lRealHandle, DWORD dwDataType,BYTE *pPacketBuffer,DWORD nPacketSize, void* pUser)
{
	
	if (dwDataType  == NET_DVR_SYSHEAD)
	{	
		g_pFile = fopen("../record/ps.dat", "wb");
		
		if (g_pFile == NULL)
		{
			printf("CreateFileHead fail\n");
			return;
		}

		fwrite(pPacketBuffer, sizeof(unsigned char), nPacketSize, g_pFile);
		printf("write head len=%d\n", nPacketSize);
	}
	else
	{
		if(g_pFile != NULL)
		{
			fwrite(pPacketBuffer, sizeof(unsigned char), nPacketSize, g_pFile);
			printf("write data len=%d\n", nPacketSize);
			//cv::Mat frame = cv::imdecode(cv::Mat(240, 320, CV_8UC1, pPacketBuffer), 1);
			//cv::imshow("Streaming", frame);
		}
	}	

}

I think that this function is the part of the code that should be changed. I have tried to develop this functionality adding the commented lines above, however it gives me this error:

terminate called after throwing an instance of 'cv::Exception'
  what():  OpenCV(4.7.0-dev) /path of the src/loadsave.cpp:800: error: (-215:Assertion failed) buf.checkVector(1, CV_8U) > 0 in function 'imdecode_'

Aborted (core dumped)

Could anyone tell me how can I solve this?

2

the input to imdecode() is a one dimensional vector, not a 2d image, like:

Mat(1, nPacketSize, CV_8UC1, pPacketBuffer)
3

I fixed it and then i got the next error:

Error: (-215)size.width>0 && size.height>0 in function imshow

I found that the matrix frame is empty after the imdecode. How can I fix it? I read in some forums that it usually happens because of the video format but I don’t know which format I need and how to change it.

4

What format is your source stream in? Is it MJPEG or RTSP?

I am pretty sure all hick cameras support RTSP so I would think it would be easier to just open the stream using the RTSP_URL as

VideoCapture cap(RTSP_URL);
Mat frame; cap.read(frame);

Note:

  1. The RTSP_URL url starts rtsp:// see the hickvision docs for info.
  2. Check that you can open the RTSP_URL in VLC media player without filling in the username and password pop up box before attempting to open it with VideoCapture.
5

That worked to me thank you!!! Here is the code if someone needs it in the future:

#include <stdio.h>
#include <opencv2/opencv.hpp>
#include <opencv2/highgui.hpp>

int main(){
    cv::VideoCapture cap;
    cap.open("rtsp://<admin>:<password>@<IP>:<RTSP port>/Streaming/channels/101");
    if(!cap.isOpened()){
        printf("Error opening video stream\n");
        return -1;
    }else{
        cv::namedWindow("video", cv::WINDOW_NORMAL);
        while(true){

            cv::Mat frame;
            cap >> frame;

            if(frame.empty()){

                break;

            }else{

                imshow("Video", frame);

                if (cv::waitKey(1)==27){

                    break;

                }
            }
        }
    }
}