Someone

videosrc = gst_element_factory_make("videotestsrc", "videotestsrc");
  videosink = gst_element_factory_make("xvimagesink", "xvimagesink");

  g_object_set (G_OBJECT (videosrc), "use-fixed-fps", FALSE, NULL);
  g_object_set (G_OBJECT (videosink), "sync", FALSE, NULL);
  g_object_set (G_OBJECT (videosrc), "is-live", TRUE, NULL);
 

  src_filter = gst_caps_new_simple ("video/x-raw-yuv", "width",
      G_TYPE_INT, 352, "height", G_TYPE_INT, 288, "framerate", GST_TYPE_FRACTION, 15,1, NULL);
  farsight_stream_set_source_filter (video_stream, src_filter);
  gst_caps_unref (src_filter);
  farsight_stream_set_source(video_stream, videosrc);
  farsight_stream_set_sink(video_stream, videosink);