Issue with Gstreamer under Qt in c++ : flow error - c++

Question

I'm a beginner in Gstreamer, I need to get the frame from an UDP camera and convert it to an cv::Mat(OpenCV).
I run my camera stream like this :
gst-launch-1.0 v4l2src device=/dev/video0 ! \
h264parse ! rtph264pay ! udpsink host=XXX.XXX.XXX.XXX port=5000
And in another terminal I can get the stream like this (and it works):
gst-launch-1.0 udpsrc port=5000 caps='application/x-rtp, media=(string)video, clock-rate=(int)90000, encoding-name=(string)H264' ! \
rtph264depay ! avdec_h264 ! autovideosink
So in my C++ code here is my C++ code :
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;
// 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(
"udpsrc port=5000 ! "
"caps=application/x-rtp, media=(string)video, clock-rate=(int)9000, encoding-name=(string)H264 ! "
"rtph264depay ! "
"avdec_h264 ! "
"videoconvert ! "
"appsink name=sink "
);
GstElement *pipeline = gst_parse_launch (descr, &error);
if (pipeline== 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);
GstStateChangeReturn test=gst_element_set_state (GST_ELEMENT (pipeline), GST_STATE_PLAYING);
qDebug() <<test<< " this is the test";
namedWindow("edges",1);
while(1) {
g_main_iteration(false);
// TODO: synchronize...
if (frameQueue.size() >10) {
// this lags pretty badly even when grabbing frames from webcam
Mat frame = frameQueue.front();
imshow("edges", frame);
cv::waitKey(30);
frameQueue.clear();
}
}
gst_element_set_state (GST_ELEMENT (pipeline), GST_STATE_NULL);
gst_object_unref (GST_OBJECT (pipeline));
return 0;
}
And I get the ERROR :
Error: Internal data flow error.
I think it is from my declaration of my pipeline, but I can't find what's wrong with it.
Any suggestions?

Answer 1

You have a ! after udpsrc port=5000. That one is not present in your original pipeline. I haven't checked any further, maybe print out the pipeline and double check if its the desired one.