使用 C++、Opencv 和 GStreamer 捕获视频时出错

Question

I have recently compiled Opencv 4.2.0 with Gstreamer 1.15.1 on 32-bit Windows platform. When I try to capture a Video using Gstreamer backend the video capture fails. Here is the code and output:

void main()
{
    VideoCapture cap("video/x-raw,format=YUV2,width=640,height=480,framerate=30/1 ! appsink", CAP_GSTREAMER);
   //VideoCapture cap(0,CAP_GSTREAMER);
    if (!cap.isOpened())
    {
        cout << "VideoCapture not opened" << endl;
        exit(-1);
    }

    Mat frame;

    while (true) {

        cap.read(frame);

        if (frame.empty())
            break;

        imshow("output", frame);
        if (waitKey(1) == 's')
            break;
    }
    destroyWindow("output");
}

Here is the output :

(testNewOpencv.exe:7392): GStreamer-CRITICAL **: 20:08:16.574: gst_element_make_
from_uri: assertion 'gst_uri_is_valid (uri)' failed
[ WARN:0] global \modules\videoio\src\cap_gstreamer.cpp (713) cv::GStreamerCapture::open OpenCV | GStreamer warning: Error opening bin: no element "video"
[ WARN:0] global \modules\videoio\src\cap_gstreamer.cpp (480) cv::GStreamerCapture::isPipelinePlaying OpenCV | GStreamer warning: GStreamer: pipeline have not been created
VideoCapture not opened

Any suggestions on resolving the issue?

Answer 1

Try this: "ksvideosrc device-index=0 ! videoscale ! videorate ! video/x-raw, width=640, height=480, framerate=30/1 ! videoconvert ! appsink"

Works for me with your code and my just built OpenCV 4.3.0, gstreamer 1.15.1, 32-bit Windows 10, USB webcam. I don't know gstreamer well enough to explain the pipeline -- I put it together from bits of search results.

I think ksvideosrc is from gst-plugins-bad.