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

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 12. 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 {
  gchar           *name_template;
  GstPadDirection  direction;
  GstPadPresence   presence;
  GstStaticCaps   static_caps;
} GstStaticPadTemplate;

Structure describing the GstStaticPadTemplate.

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 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. If you need to keep a reference to the caps, take a ref (see gst_caps_ref()).

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().

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. This functions takes ownership of the provided caps, so be sure to not use them afterwards.

name_template : the name template.
direction : the GstPadDirection of the template.
presence : the GstPadPresence of the pad.
caps : a GstCaps set for the template. The caps are taken ownership of.
Returns : a new GstPadTemplate.

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. If you need to keep a reference to the caps, take a ref (see gst_caps_ref()).

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