24 GstPadTemplate

Describe the media type of a pad.

24.1 Overview

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 <gst-caps> attached to it to describe the media type they are capable of dealing with. gst-pad-template-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 <gst-pad-presence> 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 <gst-pad-template> 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 gst-element-request-pad-by-name call to instantiate a pad from this template.

Padtemplates can be created with gst-pad-template-new or with gst-static-pad-template-get, which creates a <gst-pad-template> from a <gst-static-pad-template> that can be filled with the convenient gst-static-pad-template macro.

A padtemplate can be used to create a pad (see gst-pad-new-from-template or gst-pad-new-from-static-template) or to add to an element class (see gst-element-class-add-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-int, "
             "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 base_init of the class:

     
       static void
       my_element_base_init (gpointer g_class)
       {
         GstElementClass *gstelement_class = GST_ELEMENT_CLASS (g_class);
     
         gst_element_class_add_pad_template (gstelement_class,
             gst_static_pad_template_get (&my_template));
       }
     

Last reviewed on 2006-02-14 (0.10.3)

24.2 Usage