GstPadTemplate

GstPadTemplate — Describe the media type of a pad.

Synopsis

#include <gst/gst.h>

struct              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);
struct              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
   +----GInitiallyUnowned
         +----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_get_request_pad() 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 11. Create a pad from a padtemplate

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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: 

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static void
my_element_class_init (GstMyElementClass *klass)
{
  GstElementClass *gstelement_class = GST_ELEMENT_CLASS (klass);

  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

struct GstStaticPadTemplate

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

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. [transfer full]

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. [transfer full]

struct GstPadTemplate

struct GstPadTemplate;

The padtemplate object.

enum GstPadTemplateFlags

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

Flags for the padtemplate

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_get_request_pad().

GST_PAD_TEMPLATE_NAME_TEMPLATE()

#define GST_PAD_TEMPLATE_NAME_TEMPLATE(templ) (((GstPadTemplate *)(templ))->name_template)

Get the nametemplate of the padtemplate.

templ :

 the template to query

GST_PAD_TEMPLATE_DIRECTION()

#define GST_PAD_TEMPLATE_DIRECTION(templ) (((GstPadTemplate *)(templ))->direction)

Get the GstPadDirection of the padtemplate.

templ :

 the template to query

GST_PAD_TEMPLATE_PRESENCE()

#define GST_PAD_TEMPLATE_PRESENCE(templ) (((GstPadTemplate *)(templ))->presence)

Get the GstPadPresence of the padtemplate.

templ :

 the template to query

GST_PAD_TEMPLATE_CAPS()

#define GST_PAD_TEMPLATE_CAPS(templ)		(((GstPadTemplate *)(templ))->caps)

Get a handle to the padtemplate GstCaps

templ :

 the template to query

GST_PAD_TEMPLATE_IS_FIXED()

#define GST_PAD_TEMPLATE_IS_FIXED(templ) (GST_OBJECT_FLAG_IS_SET(templ, GST_PAD_TEMPLATE_FIXED))

Check if the properties of the padtemplate are fixed

templ :

 the template to query

gst_pad_template_new ()

GstPadTemplate *    gst_pad_template_new                (const gchar *name_template,
                                                         GstPadDirection direction,
                                                         GstPadPresence presence,
                                                         GstCaps *caps);

Creates a new pad template with a name according to the given template and with the given arguments.

name_template :

 the name template.

direction :

 the GstPadDirection of the template.

presence :

 the GstPadPresence of the pad.

caps :

 a GstCaps set for the template. [transfer none]

Returns :

 a new GstPadTemplate. [transfer floating]

gst_pad_template_get_caps ()

GstCaps *           gst_pad_template_get_caps           (GstPadTemplate *templ);

Gets the capabilities of the pad template.

templ :

 a GstPadTemplate to get capabilities of.

Returns :

 the GstCaps of the pad template. Unref after usage. [transfer full]

Property Details

The "caps" property

  "caps"                     GstCaps*              : Read / Write / Construct Only

The capabilities of the pad described by the pad template.

The "direction" property

  "direction"                GstPadDirection       : Read / Write / Construct Only

The direction of the pad described by the pad template.

Default value: GST_PAD_UNKNOWN

The "name-template" property

  "name-template"            gchar*                : Read / Write / Construct Only

The name template of the pad template.

Default value: NULL

The "presence" property

  "presence"                 GstPadPresence        : Read / Write / Construct Only

When the pad described by the pad template will become available.

Default value: GST_PAD_ALWAYS

Signal Details

The "pad-created" signal

void                user_function                      (GstPadTemplate *pad_template,
                                                        GstPad         *pad,
                                                        gpointer        user_data)         : Run Last

This signal is fired when an element creates a pad from this template.

pad_template :

 the object which received the signal.

pad :

 the pad that was created.

user_data :

 user data set when the signal handler was connected.

See Also

GstPad, GstElementFactory
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