GStreamer Basic tutorial 7 Multithreading & Pad Availability

   #include <gst/gst.h>
   
   int main(int argc, char *argv[]) {
     GstElement *pipeline, *audio_source, *tee, *audio_queue, *audio_convert, *audio_resample, *audio_sink;
     GstElement *video_queue, *visual, *video_convert, *video_sink;
     GstBus *bus;
     GstMessage *msg;
     GstPad *tee_audio_pad, *tee_video_pad;
     GstPad *queue_audio_pad, *queue_video_pad;
   
     /* Initialize GStreamer */
     gst_init (&argc, &argv);
   
     /* Create the elements */
     audio_source = gst_element_factory_make ("audiotestsrc", "audio_source");
     tee = gst_element_factory_make ("tee", "tee");
     audio_queue = gst_element_factory_make ("queue", "audio_queue");
     audio_convert = gst_element_factory_make ("audioconvert", "audio_convert");
     audio_resample = gst_element_factory_make ("audioresample", "audio_resample");
     audio_sink = gst_element_factory_make ("autoaudiosink", "audio_sink");
     video_queue = gst_element_factory_make ("queue", "video_queue");
     visual = gst_element_factory_make ("wavescope", "visual");
     video_convert = gst_element_factory_make ("videoconvert", "csp");
     video_sink = gst_element_factory_make ("autovideosink", "video_sink");
   
     /* Create the empty pipeline */
     pipeline = gst_pipeline_new ("test-pipeline");
   
     if (!pipeline || !audio_source || !tee || !audio_queue || !audio_convert || !audio_resample || !audio_sink ||
         !video_queue || !visual || !video_convert || !video_sink) {
       g_printerr ("Not all elements could be created.\n");
       return -1;
     }
   
     /* Configure elements */
     g_object_set (audio_source, "freq", 215.0f, NULL);
     g_object_set (visual, "shader", 0, "style", 1, NULL);
   
     /* Link all elements that can be automatically linked because they have "Always" pads */
     gst_bin_add_many (GST_BIN (pipeline), audio_source, tee, audio_queue, audio_convert, audio_resample, audio_sink,
         video_queue, visual, video_convert, video_sink, NULL);
     if (gst_element_link_many (audio_source, tee, NULL) != TRUE ||
         gst_element_link_many (audio_queue, audio_convert, audio_resample, audio_sink, NULL) != TRUE ||
         gst_element_link_many (video_queue, visual, video_convert, video_sink, NULL) != TRUE) {
       g_printerr ("Elements could not be linked.\n");
       gst_object_unref (pipeline);
       return -1;
     }
   
     /* Manually link the Tee, which has "Request" pads */
     tee_audio_pad = gst_element_request_pad_simple (tee, "src_%u");
     g_print ("Obtained request pad %s for audio branch.\n", gst_pad_get_name (tee_audio_pad));
     queue_audio_pad = gst_element_get_static_pad (audio_queue, "sink");
     tee_video_pad = gst_element_request_pad_simple (tee, "src_%u");
     g_print ("Obtained request pad %s for video branch.\n", gst_pad_get_name (tee_video_pad));
     queue_video_pad = gst_element_get_static_pad (video_queue, "sink");
     if (gst_pad_link (tee_audio_pad, queue_audio_pad) != GST_PAD_LINK_OK ||
         gst_pad_link (tee_video_pad, queue_video_pad) != GST_PAD_LINK_OK) {
       g_printerr ("Tee could not be linked.\n");
       gst_object_unref (pipeline);
       return -1;
     }
     gst_object_unref (queue_audio_pad);
     gst_object_unref (queue_video_pad);
   
     /* Start playing the pipeline */
     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, GST_MESSAGE_ERROR | GST_MESSAGE_EOS);
   
     /* Release the request pads from the Tee, and unref them */
     gst_element_release_request_pad (tee, tee_audio_pad);
     gst_element_release_request_pad (tee, tee_video_pad);
     gst_object_unref (tee_audio_pad);
     gst_object_unref (tee_video_pad);
   
     /* 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;
   }