GstPadTemplate

GstPadTemplate — Describe the media type of a pad.

Synopsis


#include <gst/gst.h>

                    GstStaticPadTemplate;
#define             GST_STATIC_PAD_TEMPLATE             (padname, dir, pres, caps)
GstPadTemplate*     gst_static_pad_template_get         (GstStaticPadTemplate *pad_template);
GstCaps*            gst_static_pad_template_get_caps    (GstStaticPadTemplate *templ);
                    GstPadTemplate;
enum                GstPadTemplateFlags;
enum                GstPadPresence;
#define             GST_PAD_TEMPLATE_NAME_TEMPLATE      (templ)
#define             GST_PAD_TEMPLATE_DIRECTION          (templ)
#define             GST_PAD_TEMPLATE_PRESENCE           (templ)
#define             GST_PAD_TEMPLATE_CAPS               (templ)
#define             GST_PAD_TEMPLATE_IS_FIXED           (templ)
GstPadTemplate*     gst_pad_template_new                (const gchar *name_template,
                                                         GstPadDirection direction,
                                                         GstPadPresence presence,
                                                         GstCaps *caps);
GstCaps*            gst_pad_template_get_caps           (GstPadTemplate *templ);

Object Hierarchy

  GObject
   +----GstObject
         +----GstPadTemplate

Properties

  "caps"                     GstCaps*              : Read / Write / Construct Only
  "direction"                GstPadDirection       : Read / Write / Construct Only
  "name-template"            gchar*                : Read / Write / Construct Only
  "presence"                 GstPadPresence        : Read / Write / Construct Only

Signals

  "pad-created"                                    : Run Last

Description

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 GstCaps 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 GstPadPresence 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 GstPadTemplate 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 GstPadTemplate from a GstStaticPadTemplate 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.

Example 15. 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)

Details

GstStaticPadTemplate

typedef struct {
  const gchar     *name_template;
  GstPadDirection  direction;
  GstPadPresence   presence;
  GstStaticCaps    static_caps;
} GstStaticPadTemplate;

Structure describing the GstStaticPadTemplate.

const gchar *`name_template`;	the name of the template
GstPadDirection `direction`;	the direction of the template
GstPadPresence `presence`;	the presence of the template
GstStaticCaps `static_caps`;	the caps of the template.

GST_STATIC_PAD_TEMPLATE()

#define             GST_STATIC_PAD_TEMPLATE(padname, dir, pres, caps)

Convenience macro to fill the values of a GstStaticPadTemplate structure.

`padname` :	the name template of the pad
`dir` :	the GstPadDirection of the pad
`pres` :	the GstPadPresence of the pad
`caps` :	the GstStaticCaps of the pad

gst_static_pad_template_get ()

GstPadTemplate*     gst_static_pad_template_get         (GstStaticPadTemplate *pad_template);

Converts a GstStaticPadTemplate into a GstPadTemplate.

`pad_template` :	the static pad template
Returns :	a new GstPadTemplate.

gst_static_pad_template_get_caps ()

GstCaps*            gst_static_pad_template_get_caps    (GstStaticPadTemplate *templ);

Gets the capabilities of the static pad template.

`templ` :	a GstStaticPadTemplate to get capabilities of.
Returns :	the GstCaps of the static pad template. Unref after usage. Since the core holds an additional ref to the returned caps, use `gst_caps_make_writable()` on the returned caps to modify it.

GstPadTemplate

typedef struct _GstPadTemplate GstPadTemplate;

The padtemplate object.

enum GstPadTemplateFlags

typedef enum {
  GST_PAD_TEMPLATE_FIXED        = (GST_OBJECT_FLAG_LAST << 0),
  /* padding */
  GST_PAD_TEMPLATE_FLAG_LAST    = (GST_OBJECT_FLAG_LAST << 4)
} GstPadTemplateFlags;

Flags for the padtemplate

`GST_PAD_TEMPLATE_FIXED`	the padtemplate has no variable properties
`GST_PAD_TEMPLATE_FLAG_LAST`	first flag that can be used by subclasses.

enum GstPadPresence

typedef enum {
  GST_PAD_ALWAYS,
  GST_PAD_SOMETIMES,
  GST_PAD_REQUEST
} GstPadPresence;

Indicates when this pad will become available.

`GST_PAD_ALWAYS`	the pad is always available
`GST_PAD_SOMETIMES`	the pad will become available depending on the media stream
`GST_PAD_REQUEST`	the pad is only available on request with `gst_element_request_pad_by_name()` or `gst_element_request_compatible_pad()`.