Elements
Creating a GstElement
A GstElement object is created from
a factory. To create an element, you have to get access to a
GstElementFactory object using a unique
factory name.
The following code example is used to get a factory that can be used
to create the 'mad' element, an mp3 decoder.
GstElementFactory *factory;
factory = gst_element_factory_find ("mad");
Once you have the handle to the element factory, you can create a
real element with the following code fragment:
GstElement *element;
element = gst_element_factory_create (factory, "decoder");
gst_element_factory_create will use the element
factory to create an element with the given name. The name of the
element is something you can use later on to look up the element in
a bin, for example. You can pass NULL as the name
argument to get a unique, default name.
A simple shortcut exists for creating an element from a factory. The
following example creates an element named "decoder" from the element
factory named "mad". This convenience function is most widely used to
create an element.
GstElement *element;
element = gst_element_factory_make ("mad", "decoder");
When you don't need the element anymore, you need to unref it, as shown in the following
example.
GstElement *element;
...
gst_element_unref (element);
GstElement properties
A GstElement can have several properties
which are implemented using standard GObject
properties. The usual GObject methods to query,
set and get property values and GParamSpecs
are therefore supported.
Every GstElement inherits at least
one property of its parent GstObject:
the "name" property. This is the name you provide to the
functions gst_element_factory_make or
gst_element_factory_create. You can get and set
this property using the functions
gst_object_set_name
and gst_object_get_name or use the
GObject property mechanism as shown below.
GstElement *element;
GValue value = { 0, }; /* initialize the GValue for g_object_get() */
element = gst_element_factory_make ("mad", "decoder");
g_object_set (G_OBJECT (element), "name", "mydecoder", NULL);
...
g_value_init (&value, G_TYPE_STRING);
g_object_get_property (G_OBJECT (element), "name", &value);
...
Most plugins provide additional properties to provide more information
about their configuration or to configure the element.
gst-inspect is a useful tool to query the properties
of a particular element, it will also use property introspection to give
a short explanation about the function of the property and about the
parameter types and ranges it supports.
For more information about GObject
properties we recommend you read the GObject manual and an introduction to
The Glib Object system.
GstElement signals
A GstElement also provides various
GObject signals that can be used as a flexible
callback mechanism.
More about GstElementFactory
We talk some more about the GstElementFactory object.
Getting information about an element using the factory details
Finding out what pads an element can contain
Different ways of querying the factories