<div>I have encountered a confusing problem on my jetson-TX1(gstreamer1.8,qt5.5,opencv3.2 which has been configured with gstreamer). First,I tested "gst-launch-1.0 rtspsrc location=rtsp://admin:admin12345@192.168.1.64:554/h264/ch33/main/av_stream latency=0 ! decodebin ! videoconvert ! xvimagesink sync=false" in command window and I got real-time video of my IP camera. However,when I want to use gstreamer in qt project to do opencv displaying.I tested the follow code which used appsink callback and the result is that video is not real-time and the delaying is accumulating over time.The result is unacceptable in my real-time project.Could someone help me?Best wishes to you all! #include <gst/gst.h> #include <gst/app/gstappsink.h> #include <stdlib.h> #include<QTime> #include<QDebug> #include "opencv2/opencv.hpp" using namespace cv; #define CAPS "video/x-raw,format=BGR,fFrameRate=25/1,width=1280,height=720" // TODO: use synchronized deque GMainLoop *loop; std::deque<Mat> frameQueue; int live_flag = 0; int quit_flag = 0; int sum_time=0; GstFlowReturn new_preroll(GstAppSink *appsink, gpointer data) { g_print ("Got preroll!\n"); return GST_FLOW_OK; } GstFlowReturn new_sample(GstAppSink *appsink, gpointer data) { QTime time; time.start(); static int framecount = 0; framecount++; static int width=0, height=0 ; GstSample *sample = gst_app_sink_pull_sample(appsink); GstCaps *caps = gst_sample_get_caps(sample); GstBuffer *buffer = gst_sample_get_buffer(sample); static GstStructure *s; const GstStructure *info = gst_sample_get_info(sample); // ---- get width and height if(framecount==1) { if(!caps) { g_print("Could not get image info from filter caps"); exit(-11); } s = gst_caps_get_structure(caps,0); gboolean res = gst_structure_get_int(s, "width", &width); res |= gst_structure_get_int(s, "height", &height); if(!res) { g_print("Could not get image width and height from filter caps"); exit(-12); } g_print("Image size: %d\t%d\n",width,height); } // ---- 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(width, height), CV_8UC3, (char*)map.data, Mat::AUTO_STEP); // this lags pretty badly even when grabbing frames from webcam //Mat edges; //cvtColor(frame, edges, CV_RGB2GRAY); //GaussianBlur(edges, edges, Size(7,7), 1.5, 1.5); //Canny(edges, edges, 0, 30, 3); imshow("stream", frame); //char key = cv::waitKey(10); //if(key!=-1) quit_flag = 1; 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); sum_time =time.elapsed(); qDebug()<<"time:"<<sum_time<<"\n"; return GST_FLOW_OK; } static gboolean my_bus_callback (GstBus *bus, GstMessage *message, gpointer data) { g_print ("Got %s message from %s\n", GST_MESSAGE_TYPE_NAME (message), GST_OBJECT_NAME (message->src)); switch (GST_MESSAGE_TYPE (message)) { case GST_MESSAGE_ERROR: { GError *err; gchar *debug; gst_message_parse_error (message, &err, &debug); g_print ("Error from %s: %s\n", GST_OBJECT_NAME (message->src), err->message); g_error_free (err); g_free (debug); break; } case GST_MESSAGE_EOS: /* end-of-stream */ quit_flag = 1; break; case GST_MESSAGE_STATE_CHANGED: GstState oldstate, newstate; gst_message_parse_state_changed(message, &oldstate, &newstate, NULL); g_print ("Element %s changed state from %s to %s.\n", GST_OBJECT_NAME (message->src), gst_element_state_get_name (oldstate), gst_element_state_get_name (newstate)); 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; GstElement *pipeline, *sink; GstStateChangeReturn state_ret; GstSample *sample; gst_init (&argc, &argv); gchar *descr = g_strdup( "rtspsrc location=rtsp://admin:admin12345@192.168.1.64:554/h264/ch33/main/av_stream latency=0 ! " "decodebin ! " "videoconvert ! " "appsink name=sink sync=false" ); // gchar *descr = g_strdup( // "rtspsrc location=\"rtsp://admin:admin12345@192.168.1.64:554/h264/ch33/main/av_stream\" latency=0 ! " // "decodebin ! " // "videoconvert ! " // "xvimagesink name=sink sync=true" // ); 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 */ sink = gst_bin_get_by_name (GST_BIN (pipeline), "sink"); /*set to pause*/ state_ret = gst_element_set_state(pipeline, GST_STATE_PAUSED); switch(state_ret) { case GST_STATE_CHANGE_FAILURE: g_print ("failed to play the file\n"); exit (-2); case GST_STATE_CHANGE_NO_PREROLL: /* for live sources, we need to set the pipeline to PLAYING before we can * receive a buffer. */ g_print ("live source detected\n"); live_flag = 1; break; default: break; } 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("stream",1); loop = g_main_loop_new(NULL,false); g_main_loop_run(loop); cv::destroyWindow("stream"); g_print ("Going to end of main!\n"); gst_element_set_state (GST_ELEMENT (pipeline), GST_STATE_NULL); gst_object_unref (GST_OBJECT (pipeline)); return 0; } </div>