gstreamer rtsp tee appsink can't emit signal new-sample - c++

Question

I am using gstreamer to play and slove the rtsp stream.
rtspsrc location=rtspt://admin:scut123456#192.168.1.64:554/Streaming/Channels/1 ! tee name=t ! queue ! decodebin ! videoconvert ! autovideosink t. ! queue ! rtph264depay ! h264parse ! appsink name=mysink
and i write in c++ code like this :
#include <gst/gst.h>
void printIt(GList *p) {
if(!p) {
g_print("p null\n");
return ;
}
while(p) {
GstPad *pad = (GstPad*)p->data;
g_print("[%s]", pad->object.name);
p = p->next;
}
g_print("\n");
}
GstFlowReturn new_sample_cb (GstElement * appsink, gpointer udata) {
g_print("new-sample cb\n");
return GST_FLOW_OK;
}
GstFlowReturn new_preroll_cb (GstElement* appsink, gpointer udata) {
g_print("new_preroll_cb cb\n");
return GST_FLOW_OK;
}
int
main (int argc, char *argv[]) {
GstElement *pipeline;
GstBus *bus;
GstMessage *msg;
/* Initialize GStreamer */
gst_init (&argc, &argv);
/* Build the pipeline */
pipeline = gst_parse_launch("rtspsrc location=rtspt://admin:scut123456#192.168.1.64:554/Streaming/Channels/1 ! tee name=t ! queue ! decodebin ! videoconvert ! autovideosink t. ! queue ! rtph264depay ! h264parse ! appsink name=mysink", NULL);
GstElement *appsink = gst_bin_get_by_name(GST_BIN(pipeline), "mysink");
printIt(appsink->pads);
g_signal_connect(appsink, "new-sample", G_CALLBACK(new_sample_cb), pipeline);
g_print("sig conn new-sample\n");
g_signal_connect(appsink, "new-preroll", G_CALLBACK(new_preroll_cb), pipeline);
g_print("sig conn new-preroll\n");
/* Start playing */
gst_element_set_state (pipeline, GST_STATE_PLAYING);
/* Wait until error or EOS */
bus = gst_element_get_bus (pipeline);
msg =
gst_bus_timed_pop_filtered (bus, GST_CLOCK_TIME_NONE,
GstMessageType(GST_MESSAGE_ERROR | GST_MESSAGE_EOS));
/* Free resources */
if (msg != NULL)
gst_message_unref (msg);
gst_object_unref (bus);
gst_element_set_state (pipeline, GST_STATE_NULL);
gst_object_unref (pipeline);
return 0;
}
when i compile and run it. it has output video in the autovideosink but the appsink's signal new-sample is not be callbacked. what should i do if i what to slove a frame in appsink ?
thanks.

Answer 1

By default appsink favors to use callbacks instead of signals for performance reasons (but I wouldn't consider your use case as a performance problem). For appsink to emit signals you will need to set the emit-signals property of the appsink to true. It defaults to false.
P.S. Apart from the above, I think you will need a GMainLoop for the event processing as demonstrated in the GStreamer examples.