Chapter 4. Specifying the pads

As explained before, pads are the port through which data goes in and out of your element, and that makes them a very important item in the process of element creation. In the boilerplate code, we have seen how static pad templates take care of registering pad templates with the element class. Here, we will see how to create actual elements, use an _event ()-function to configure for a particular format and how to register functions to let data flow through the element.

In the element _init () function, you create the pad from the pad template that has been registered with the element class in the _class_init () function. After creating the pad, you have to set a _chain () function pointer that will receive and process the input data on the sinkpad. You can optionally also set an _event () function pointer and a _query () function pointer. Alternatively, pads can also operate in looping mode, which means that they can pull data themselves. More on this topic later. After that, you have to register the pad with the element. This happens like this:




static void
gst_my_filter_init (GstMyFilter *filter)
{
  /* pad through which data comes in to the element */
  filter->sinkpad = gst_pad_new_from_static_template (
	&sink_template, "sink");
  /* pads are configured here with gst_pad_set_*_function () */



  gst_element_add_pad (GST_ELEMENT (filter), filter->sinkpad);

  /* pad through which data goes out of the element */
  filter->srcpad = gst_pad_new_from_static_template (
	&src_template, "src");
  /* pads are configured here with gst_pad_set_*_function () */



  gst_element_add_pad (GST_ELEMENT (filter), filter->srcpad);

  /* properties initial value */
  filter->silent = FALSE;
}