Padtemplates describe the possible media types a pad or an elementfactory can handle.
This allows for both inspection of handled types before loading the element plugin as well as identifying pads on elements that are not yet created (request or sometimes pads).
Pad and PadTemplates have Caps attached to it to describe the media type they are capable of
dealing with. get_caps or GST_PAD_TEMPLATE_CAPS are used to get
the caps of a padtemplate. It's not possible to modify the caps of a padtemplate after creation.
PadTemplates have a PadPresence property which identifies the lifetime of the pad and
that can be retrieved with GST_PAD_TEMPLATE_PRESENCE. Also the direction of the pad can be retrieved from the
PadTemplate with GST_PAD_TEMPLATE_DIRECTION.
The GST_PAD_TEMPLATE_NAME_TEMPLATE is important for GST_PAD_REQUEST pads because it has to be used as the name in the
request_pad_simple call to instantiate a pad from this template.
Padtemplates can be created with PadTemplate or with
@get, which creates a PadTemplate from a
StaticPadTemplate that can be filled with the convenient
GST_STATIC_PAD_TEMPLATE macro.
A padtemplate can be used to create a pad (see Pad.from_template or Pad.from_static_template) or to add to an element class (see add_static_pad_template).
The following code example shows the code to create a pad from a padtemplate.
GstStaticPadTemplate my_template =
GST_STATIC_PAD_TEMPLATE (
"sink", // the name of the pad
GST_PAD_SINK, // the direction of the pad
GST_PAD_ALWAYS, // when this pad will be present
GST_STATIC_CAPS ( // the capabilities of the padtemplate
"audio/x-raw, "
"channels = (int) [ 1, 6 ]"
)
);
void
my_method (void)
{
GstPad *pad;
pad = gst_pad_new_from_static_template (&my_template, "sink");
...
}The following example shows you how to add the padtemplate to an element class, this is usually done in the class_init of the class:
static void
my_element_class_init (GstMyElementClass *klass)
{
GstElementClass *gstelement_class = GST_ELEMENT_CLASS (klass);
gst_element_class_add_static_pad_template (gstelement_class, &my_template);
}