8.2. Events

Events are control particles that are sent both up- and downstream in a pipeline along with buffers. Downstream events notify fellow elements of stream states. Possible events include discontinuities, flushes, end-of-stream notifications and so on. Upstream events are used both in application-element interaction as well as event-event interaction to request changes in stream state, such as seeks. For applications, only upstream events are important. Downstream events are just explained to get a more complete picture of the data concept.

Since most applications seek in time units, our example below does so too:

static void
seek_to_time (GstElement *element,
	      guint64     time_ns)
{
  GstEvent *event;

  event = gst_event_new_seek (GST_SEEK_METHOD_SET |
			      GST_FORMAT_TIME,
			      time_ns);
  gst_element_send_event (element, event);
}
    

The function gst_element_seek () is a shortcut for this. This is mostly just to show how it all works.