gstreamer example

/*
   GStreamer example
   Compiles with : gcc `pkg-config --cflags --libs gstreamer-0.10` -o gst_example gst_example.c

   Detailed explanation and example footprint was shown here...
   http://ishikawa-vision.org/~kyamagu/cgi-bin/moin.cgi/VideoTexture/

*/
#include <gst/gst.h>
#include <glib.h>

// if you require uncomment
//#define USB_CAM
//#define IEEE1394

/* callback prototype */
static gbooleanbus_handler(GstBus  *bus, GstMessage *msg, gpointer data);

/* main */
int main(int argc, char *argv[])
{
  GMainLoop *loop;
  GstElement *pipeline, *source, *sink;
  GstBus *bus;

  /** (1) Initialisation **/
  gst_init(&argc, &argv);

  /** (2) Objects instantiation **/
  loop = g_main_loop_new(NULL, FALSE);

  /* Create gstreamer elements */
  pipeline = gst_pipeline_new("testpipeline");
#if defined(USB_CAM)
  //g_object_set(v4l2sink, "device", "/dev/video1", NULL);
  source   = gst_element_factory_make("v4l2src", "videosrc");        /* use usb cam */
#elif defined(IEEE1394)
  source   = gst_element_factory_make("dc1394src", "videosrc");     /* use IEEE1394 cam */
#else
  source   = gst_element_factory_make("videotestsrc", "videosrc");
#endif
  sink     = gst_element_factory_make("fakesink", "fakesink");
  if (!pipeline || !source || !sink) {
    g_printerr("One element could not be created. Exiting.\n");
    return -1;
  }

  /** (3) Set up the pipeline **/
  /* we set the sync property of fakesink to TRUE */
  g_object_set(G_OBJECT (sink), "sync", TRUE, NULL);

  /* we add a message handler */
  bus = gst_pipeline_get_bus(GST_PIPELINE (pipeline));
  gst_bus_add_watch(bus, bus_handler, loop);
  gst_object_unref(bus);

  /* we add all elements into the pipeline */
  gst_bin_add_many(GST_BIN (pipeline), source, sink, NULL);

  /* we link the elements together */
  gst_element_link(source, sink);

  /** (4) Main loop **/
  /* Set the pipeline to "playing" state */
  gst_element_set_state(pipeline, GST_STATE_PLAYING);

  g_main_loop_run(loop);

  /* Out of the main loop, clean up nicely */
  // delete the memory allocated to the main loop
  g_main_loop_unref(loop);
  // When you don't need the element anymore, you need to unref it using gst_object_unref ().
  // This decreases the reference count for the element by 1. An element has a refcount of 1 when
  // it gets created. An element gets destroyed completely when the refcount is decreased to 0.
  // ref :- https://www.cnblogs.com/fellow1988/p/12892254.html
  //
  gst_object_unref(GST_OBJECT (source));
  gst_object_unref(GST_OBJECT (sink));
  // same for the pipeline memory
  gst_element_set_state(pipeline, GST_STATE_NULL);
  gst_object_unref(GST_OBJECT (pipeline));
  gst_deinit();

  return 0;
}

/* callback implementation */
static gboolean bus_handler(GstBus  *bus, GstMessage *msg, gpointer data)
{
  GMainLoop *loop = (GMainLoop *) data;

  switch (GST_MESSAGE_TYPE (msg)) {
    case GST_MESSAGE_ERROR: {
      gchar  *debug;
      GError *error;

      gst_message_parse_error(msg, &error, &debug);
      g_free (debug);
      g_printerr("Error: %s\n", error->message);
      g_error_free (error);

      g_main_loop_quit(loop);
      break;
    }
    default:
      break;
  }

  return TRUE;
}