Simple RTSP Pipeline Works with gst-launch But Not with API

[Zheng]

Thanks! @Sebastian Dröge-3 and @Michael Gruner

The problem is exactly the one Sebastian said. The rtspsrc's sink pad is not
a static one. So a on_pad_added callback function is needed. The following
is the working C functions.

static void on_pad_added(GstElement *element, GstPad *pad, gpointer data) {
	gchar *name;
	name = gst_pad_get_name(pad);
	g_print("A new pad %s was created.\n", name);
	g_free(name);

	GstPad *sinkpad;
	GstElement *downstream = (GstElement *) data;

	sinkpad = gst_element_get_static_pad(downstream, "sink");

	gst_pad_link (pad, sinkpad);

	gst_object_unref(sinkpad);
}

int startPipeline(const char *vs_location, const char *socket_path) {
	puts(vs_location);
	puts(socket_path);

	GstElement *pipeline;
	GstBus *bus;
	guint bus_watch_id;

	gst_init(NULL, NULL);
	pipeline = gst_pipeline_new("my_pipeline");
	bus = gst_pipeline_get_bus(GST_PIPELINE(pipeline));
	bus_watch_id = gst_bus_add_watch(bus, bus_callback, NULL);
	gst_object_unref(bus);

	GstElement *source, *dec_bin, *v_conv, *sink;
	source = gst_element_factory_make("rtspsrc", "source");
	dec_bin = gst_element_factory_make("decodebin", "dec_bin");
	v_conv = gst_element_factory_make("videoconvert", "v_con");
	sink = gst_element_factory_make("autovideosink", "sink");
	gst_bin_add_many(GST_BIN(pipeline), source, dec_bin, v_conv, sink, NULL);

	// Set element properties.
	g_object_set(G_OBJECT(source), "port-range", "5000-5100", NULL);
	g_object_set(G_OBJECT(source), "location", vs_location, NULL);
	g_object_set(G_OBJECT(source), "latency", 0, NULL);

	g_signal_connect(source, "pad-added", G_CALLBACK(on_pad_added), dec_bin);
	g_signal_connect(dec_bin, "pad-added", G_CALLBACK(on_pad_added), v_conv);

	GstCaps *caps;
	caps = gst_caps_new_simple(
			"video/x-raw",
			"width", G_TYPE_INT, 640,
			"height", G_TYPE_INT, 480,
			"format", G_TYPE_STRING, "YUY2",
			NULL);
	if(gst_element_link_filtered(v_conv, sink, caps) == FALSE) {
		g_printerr("Error: gst_element_link_filtered() failed.\n");

		gst_element_set_state(pipeline, GST_STATE_NULL);
		gst_object_unref(pipeline);
		g_source_remove(bus_watch_id);

		return -1;
	}
	gst_caps_unref(caps);

	gst_element_set_state(pipeline, GST_STATE_PLAYING);

	loop = g_main_loop_new(NULL, FALSE);
	g_main_loop_run(loop);

	// Clean up.
	gst_element_set_state(pipeline, GST_STATE_NULL);
	gst_object_unref(pipeline);
	g_source_remove(bus_watch_id);
	g_main_loop_unref(loop);

	return 0;
}



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