in mqtt-publish-sample/mqttpublisher-gstreamer-plugin/mqttpublisher/gstmqttpublisher.cc [99:113]
static void gst_mqtt_publisher_init(GstMqttPublisher * filter) {
filter->sinkpad = gst_pad_new_from_static_template(&sink_factory, "sink");
gst_pad_set_event_function(filter->sinkpad, GST_DEBUG_FUNCPTR(gst_mqtt_publisher_sink_event));
gst_pad_set_chain_function(filter->sinkpad, GST_DEBUG_FUNCPTR(gst_mqtt_publisher_chain));
GST_PAD_SET_PROXY_CAPS(filter->sinkpad);
gst_element_add_pad(GST_ELEMENT (filter), filter->sinkpad);
filter->srcpad = gst_pad_new_from_static_template(&src_factory, "src");
GST_PAD_SET_PROXY_CAPS(filter->srcpad);
gst_element_add_pad(GST_ELEMENT (filter), filter->srcpad);
// Set default properties
filter->publish_topic = g_strdup("lookoutvision/anomalydetection/result");
filter->greengrass_client = new GreengrassClient();
}