viewer: try to fix display latency issues

Sometimes, the framerate returned by the camera is not the actual
framerate of the received stream. An actual framerate greater than the
one given by the camera causes shoppy video.

Also, sometimes at start the display latency is too big (1 second or
more).

Setting the framerate in the appsrc caps to 0 Hz seems to fix this
issues.

viewer/arvviewer.c

@@ -928,12 +928,12 @@ start_video (ArvViewer *viewer)
 	gst_caps_set_simple (caps,
 			     "width", G_TYPE_INT, width,
 			     "height", G_TYPE_INT, height,
-			     "framerate", GST_TYPE_FRACTION, (unsigned int ) (double) (0.5 + frame_rate), 1,
+			     "framerate", GST_TYPE_FRACTION, 0, 1,
 			     NULL);
 	gst_app_src_set_caps (GST_APP_SRC (viewer->appsrc), caps);
 	gst_caps_unref (caps);
 
-	g_object_set(G_OBJECT (viewer->appsrc), "format", GST_FORMAT_TIME, NULL);
+	g_object_set(G_OBJECT (viewer->appsrc), "format", GST_FORMAT_TIME, "is-live", TRUE, "do-timestamp", TRUE, NULL);
 
 	if (!has_gtkglsink && !has_gtksink) {
 		GstBus *bus;