#include <gst/gst.h>/* Structure to contain all our information, so we can pass it to callbacks */
typedef struct _CustomData {GstElement *pipeline;GstElement *source;GstElement *convert;GstElement *sink;
} CustomData;/* Handler for the pad-added signal */
static void pad_added_handler (GstElement *src, GstPad *pad, CustomData *data);int main(int argc, char *argv[]) {CustomData data;GstBus *bus;GstMessage *msg;GstStateChangeReturn ret;gboolean terminate = FALSE;/* Initialize GStreamer */gst_init (&argc, &argv);/* Create the elements */data.source = gst_element_factory_make ("uridecodebin", "source");data.convert = gst_element_factory_make ("audioconvert", "convert");data.sink = gst_element_factory_make ("autoaudiosink", "sink");/* Create the empty pipeline */data.pipeline = gst_pipeline_new ("test-pipeline");if (!data.pipeline || !data.source || !data.convert || !data.sink) {g_printerr ("Not all elements could be created.\n");return -1;}/* Build the pipeline. Note that we are NOT linking the source at this* point. We will do it later. */gst_bin_add_many (GST_BIN (data.pipeline), data.source, data.convert , data.sink, NULL);if (!gst_element_link (data.convert, data.sink)) {g_printerr ("Elements could not be linked.\n");gst_object_unref (data.pipeline);return -1;}/* Set the URI to play */g_object_set (data.source, "uri", "https://www.freedesktop.org/software/gstreamer-sdk/data/media/sintel_trailer-480p.webm", NULL);/* Connect to the pad-added signal */g_signal_connect (data.source, "pad-added", G_CALLBACK (pad_added_handler), &data);/* Start playing */ret = gst_element_set_state (data.pipeline, GST_STATE_PLAYING);if (ret == GST_STATE_CHANGE_FAILURE) {g_printerr ("Unable to set the pipeline to the playing state.\n");gst_object_unref (data.pipeline);return -1;}/* Listen to the bus */bus = gst_element_get_bus (data.pipeline);do {msg = gst_bus_timed_pop_filtered (bus, GST_CLOCK_TIME_NONE,GST_MESSAGE_STATE_CHANGED | GST_MESSAGE_ERROR | GST_MESSAGE_EOS);/* Parse message */if (msg != NULL) {GError *err;gchar *debug_info;switch (GST_MESSAGE_TYPE (msg)) {case GST_MESSAGE_ERROR:gst_message_parse_error (msg, &err, &debug_info);g_printerr ("Error received from element %s: %s\n", GST_OBJECT_NAME (msg->src), err->message);g_printerr ("Debugging information: %s\n", debug_info ? debug_info : "none");g_clear_error (&err);g_free (debug_info);terminate = TRUE;break;case GST_MESSAGE_EOS:g_print ("End-Of-Stream reached.\n");terminate = TRUE;break;case GST_MESSAGE_STATE_CHANGED:/* We are only interested in state-changed messages from the pipeline */if (GST_MESSAGE_SRC (msg) == GST_OBJECT (data.pipeline)) {GstState old_state, new_state, pending_state;gst_message_parse_state_changed (msg, &old_state, &new_state, &pending_state);g_print ("Pipeline state changed from %s to %s:\n",gst_element_state_get_name (old_state), gst_element_state_get_name (new_state));}break;default:/* We should not reach here */g_printerr ("Unexpected message received.\n");break;}gst_message_unref (msg);}} while (!terminate);/* Free resources */gst_object_unref (bus);gst_element_set_state (data.pipeline, GST_STATE_NULL);gst_object_unref (data.pipeline);return 0;
}/* This function will be called by the pad-added signal */
static void pad_added_handler (GstElement *src, GstPad *new_pad, CustomData *data) {GstPad *sink_pad = gst_element_get_static_pad (data->convert, "sink");GstPadLinkReturn ret;GstCaps *new_pad_caps = NULL;GstStructure *new_pad_struct = NULL;const gchar *new_pad_type = NULL;g_print ("Received new pad '%s' from '%s':\n", GST_PAD_NAME (new_pad), GST_ELEMENT_NAME (src));/* If our converter is already linked, we have nothing to do here */if (gst_pad_is_linked (sink_pad)) {g_print ("We are already linked. Ignoring.\n");goto exit;}/* Check the new pad's type */new_pad_caps = gst_pad_get_current_caps (new_pad);new_pad_struct = gst_caps_get_structure (new_pad_caps, 0);new_pad_type = gst_structure_get_name (new_pad_struct);if (!g_str_has_prefix (new_pad_type, "audio/x-raw")) {g_print ("It has type '%s' which is not raw audio. Ignoring.\n", new_pad_type);goto exit;}/* Attempt the link */ret = gst_pad_link (new_pad, sink_pad);if (GST_PAD_LINK_FAILED (ret)) {g_print ("Type is '%s' but link failed.\n", new_pad_type);} else {g_print ("Link succeeded (type '%s').\n", new_pad_type);}exit:/* Unreference the new pad's caps, if we got them */if (new_pad_caps != NULL)gst_caps_unref (new_pad_caps);/* Unreference the sink pad */gst_object_unref (sink_pad);
}

/* Create the elements */
data.source = gst_element_factory_make ("uridecodebin", "source");
data.convert = gst_element_factory_make ("audioconvert", "convert");
data.sink = gst_element_factory_make ("autoaudiosink", "sink");

if (!gst_element_link (data.convert, data.sink)) {g_printerr ("Elements could not be linked.\n");gst_object_unref (data.pipeline);return -1;
}

/* Set the URI to play */
g_object_set (data.source, "uri", "https://www.freedesktop.org/software/gstreamer-sdk/data/media/sintel_trailer-480p.webm", NULL);

/* Connect to the pad-added signal */
g_signal_connect (data.source, "pad-added", G_CALLBACK (pad_added_handler), &data);

static void pad_added_handler (GstElement *src, GstPad *new_pad, CustomData *data) {

$ gst-inspect-1.0 uridecodebin
...
Element Signals:"pad-added" :  void user_function (GstElement* object,GstPad* arg0,gpointer user_data);
...                              

GstPad *sink_pad = gst_element_get_static_pad (data->convert, "sink");

/* If our converter is already linked, we have nothing to do here */
if (gst_pad_is_linked (sink_pad)) {g_print ("We are already linked. Ignoring.\n");goto exit;
}

/* Check the new pad's type */
new_pad_caps = gst_pad_get_current_caps (new_pad, NULL);
new_pad_struct = gst_caps_get_structure (new_pad_caps, 0);
new_pad_type = gst_structure_get_name (new_pad_struct);
if (!g_str_has_prefix (new_pad_type, "audio/x-raw")) {g_print ("It has type '%s' which is not raw audio. Ignoring.\n", new_pad_type);goto exit;
}

/* Attempt the link */
ret = gst_pad_link (new_pad, sink_pad);
if (GST_PAD_LINK_FAILED (ret)) {g_print ("Type is '%s' but link failed.\n", new_pad_type);
} else {g_print ("Link succeeded (type '%s').\n", new_pad_type);
}

case GST_MESSAGE_STATE_CHANGED:/* We are only interested in state-changed messages from the pipeline */if (GST_MESSAGE_SRC (msg) == GST_OBJECT (data.pipeline)) {GstState old_state, new_state, pending_state;gst_message_parse_state_changed (msg, &old_state, &new_state, &pending_state);g_print ("Pipeline state changed from %s to %s:\n",gst_element_state_get_name (old_state), gst_element_state_get_name (new_state));}break;