Using opencv processing (cv::imshow cv::cvtColor) in Gstreamer application (appsink)

I want to use appsink to extract the frames in the Gstbuffer in the pipeline, and then use opencv for image processing, I refer to the program in this link (Adding opencv processing to gstreamer application), but when I use imshow or cvtColor in the main function, there will be a core dump error, But in the new_sample function, I should have successfully extracted each frame in the buffer, and the map.size is also correct (BGR, width=100, height=100, map.size=30000).

opencv version:4.7.0

video/x-raw, format=(string)BGR, width=(int)100, height=(int)100, framerate=(fraction)30/1, multiview-mode=(string)mono, pixel-aspect-ratio=(fraction)1/1, interlace-mode=(string)progressive Erreur de segmentation (core dumped)

Gtk-Message: 17:04:05.146: Failed to load module "appmenu-gtk-module" frameSize: 30000 video/x-raw, format=(string)BGR, width=(int)100, height=(int)100, framerate=(fraction)30/1, multiview-mode=(string)mono, pixel-aspect-ratio=(fraction)1/1, interlace-mode=(string)progressive frameSize: 30000 Erreur de segmentation (core dumped)

#include <gst/gst.h>
#include <gst/app/app.h>
#include <gst/app/gstappsink.h>
#include <stdlib.h> 
#include <opencv2/opencv.hpp>
#include <opencv2/core.hpp>
#include <opencv2/videoio.hpp>
#include <opencv2/highgui.hpp>
using namespace cv;

// TODO: use synchronized deque
std::deque<Mat> frameQueue;

 

GstFlowReturn
new_preroll(GstAppSink *appsink, gpointer data) {
  g_print ("Got preroll!\n");
  return GST_FLOW_OK;
}

 

GstFlowReturn
new_sample(GstAppSink *appsink, gpointer data) {
  static int framecount = 0;
  framecount++;

 

  GstSample *sample = gst_app_sink_pull_sample(appsink);
  GstCaps *caps = gst_sample_get_caps(sample);
  GstBuffer *buffer = gst_sample_get_buffer(sample);
  const GstStructure *info = gst_sample_get_info(sample);

 

  // ---- Read frame and convert to opencv format ---------------
  GstMapInfo map;
  gst_buffer_map (buffer, &map, GST_MAP_READ);
  // convert gstreamer data to OpenCV Mat, you could actually
  // resolve height / width from caps...
  Mat frame(Size(320, 240), CV_8UC3, (char*)map.data, Mat::AUTO_STEP);
  int frameSize = map.size;
  g_print ("frameSize: %d\n",frameSize);
  // TODO: synchronize this....
  frameQueue.push_back(frame);
  gst_buffer_unmap(buffer, &map);

  // ------------------------------------------------------------
  // print dot every 30 frames
  if (framecount%30 == 0) {
    g_print (".");
  }

  // show caps on first frame
  if (framecount == 1) {
    g_print ("%s\n", gst_caps_to_string(caps));
  }
  gst_sample_unref (sample);
  return GST_FLOW_OK;
}

 

static gboolean
my_bus_callback (GstBus *bus, GstMessage *message, gpointer data) {
  g_print ("Got %s message\n", GST_MESSAGE_TYPE_NAME (message));
  switch (GST_MESSAGE_TYPE (message)) {
    case GST_MESSAGE_ERROR: {
      GError *err;
      gchar *debug;

 

      gst_message_parse_error (message, &err, &debug);
      g_print ("Error: %s\n", err->message);
      g_error_free (err);
      g_free (debug);    
      break;
    }
    case GST_MESSAGE_EOS:
      /* end-of-stream */
      break;
    default:
      /* unhandled message */
      break;
  }
  /* we want to be notified again the next time there is a message
   * on the bus, so returning TRUE (FALSE means we want to stop watching
   * for messages on the bus and our callback should not be called again)
   */
  return TRUE;
}

 

int
main (int argc, char *argv[])
{
  GError *error = NULL;

 

  gst_init (&argc, &argv);

 

  gchar *descr = g_strdup(
    "videotestsrc  pattern=ball ! "
    "video/x-raw,width=100,height=100,format=(string)BGR ! "
    "videoconvert ! "
    "appsink name=sink sync=true"
  );
  GstElement *pipeline = gst_parse_launch (descr, &error);

 

  if (error != NULL) {
    g_print ("could not construct pipeline: %s\n", error->message);
    g_error_free (error);
    exit (-1);
  }


  /* get sink */
  GstElement *sink = gst_bin_get_by_name (GST_BIN (pipeline), "sink");

  gst_app_sink_set_emit_signals((GstAppSink*)sink, true);
  gst_app_sink_set_drop((GstAppSink*)sink, true);
  gst_app_sink_set_max_buffers((GstAppSink*)sink, 1);
  GstAppSinkCallbacks callbacks = { NULL, new_preroll, new_sample };
  gst_app_sink_set_callbacks (GST_APP_SINK(sink), &callbacks, NULL, NULL);


  GstBus *bus;
  guint bus_watch_id;
  bus = gst_pipeline_get_bus (GST_PIPELINE (pipeline));
  bus_watch_id = gst_bus_add_watch (bus, my_bus_callback, NULL);
  gst_object_unref (bus);

 
  gst_element_set_state (GST_ELEMENT (pipeline), GST_STATE_PLAYING);
  namedWindow("edges",1);
  while(1) {
    g_main_iteration(false);

      // TODO: synchronize...
    if (frameQueue.size() > 0) {
      // this lags pretty badly even when grabbing frames from webcam
      Mat frame = frameQueue.front();
      Mat edges;
      cvtColor(frame, edges, cv::COLOR_BGR2GRAY);
      //GaussianBlur(edges, edges, Size(7,7), 1.5, 1.5);
      //Canny(edges, edges, 0, 30, 3);
      //imshow("edges", edges);
      //cv::waitKey(30);
      frameQueue.clear();
    }
  }  

  gst_element_set_state (GST_ELEMENT (pipeline), GST_STATE_NULL);
  gst_object_unref (GST_OBJECT (pipeline));

I'm a newbie and would appreciate some help, many thanks!