# Trouble with openCV getting a stream using a Hikvision camera
**URL:** https://forum.opencv.org/t/trouble-with-opencv-getting-a-stream-using-a-hikvision-camera/12886
**Category:** C++
**Created:** [April 20, 2023, 12:49pm UTC](https://forum.opencv.org/t/trouble-with-opencv-getting-a-stream-using-a-hikvision-camera/12886 "2023-04-20T12:49:15Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@apayan](https://forum.opencv.org/u/apayan)
#### Post date: [April 20, 2023, 12:49pm UTC](https://forum.opencv.org/t/trouble-with-opencv-getting-a-stream-using-a-hikvision-camera/12886/1 "2023-04-20T12:49:15Z")
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-/](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.
```auto
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:
```auto
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?
---
### Author:  [@berak](https://forum.opencv.org/u/berak)
#### Post date: [April 20, 2023, 1:49pm UTC](https://forum.opencv.org/t/trouble-with-opencv-getting-a-stream-using-a-hikvision-camera/12886/2 "2023-04-20T13:49:17Z")
the input to imdecode() is a one dimensional vector, not a 2d image, like:
```
Mat(1, nPacketSize, CV_8UC1, pPacketBuffer)
```
---
### Author:  [@apayan](https://forum.opencv.org/u/apayan)
#### Post date: [April 21, 2023, 8:05am UTC](https://forum.opencv.org/t/trouble-with-opencv-getting-a-stream-using-a-hikvision-camera/12886/3 "2023-04-21T08:05:41Z")
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.
---
### Author:  [@cudawarped](https://forum.opencv.org/u/cudawarped)
#### Post date: [April 21, 2023, 9:01am UTC](https://forum.opencv.org/t/trouble-with-opencv-getting-a-stream-using-a-hikvision-camera/12886/4 "2023-04-21T09:01:51Z")
> [@apayan](#):
>
> 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.
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
```auto
VideoCapture cap(RTSP_URL);
Mat frame; cap.read(frame);
```
Note:
1. The RTSP\_URL url starts `rtsp://` see the [hickvision docs](https://supportusa.hikvision.com/support/solutions/articles/17000129064-how-do-i-get-my-rtsp-stream-) 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`.
---
### Author:  [@apayan](https://forum.opencv.org/u/apayan)
#### Post date: [April 21, 2023, 10:48am UTC](https://forum.opencv.org/t/trouble-with-opencv-getting-a-stream-using-a-hikvision-camera/12886/5 "2023-04-21T10:48:22Z")
That worked to me thank you!!! Here is the code if someone needs it in the future:
```auto
#include
#include
#include
int main(){
cv::VideoCapture cap;
cap.open("rtsp://:@:/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;
}
}
}
}
}
```