mirror of
https://gitlab.freedesktop.org/gstreamer/gstreamer.git
synced 2024-11-18 07:47:17 +00:00
77 lines
3.8 KiB
Text
77 lines
3.8 KiB
Text
gstelement
|
|
name
|
|
pads
|
|
state
|
|
loopfunction
|
|
threadstate
|
|
manager
|
|
ghostpads
|
|
|
|
GstElement
|
|
==========
|
|
|
|
The Element is the most important object in the entire GStreamer system, as it defines the structure of the pipeline.
|
|
Elements include sources, filters, sinks, and containers (Bins). They may be an intrinsic part of the core GStreamer
|
|
library, or may be loaded from a plugin. In some cases they're even fabricated from completely different systems (see
|
|
the LADSPA plugin). They are generally created from a GstElementFactory, which will be covered in another chapter, but
|
|
for the intrinsic types they can be created with specific functions.
|
|
|
|
Elements contains GstPads (also covered in another chapter), which are subsequently used to connect the Elements
|
|
together to form a pipeline capable of passing and processing data. They have a parent, which must be another Element.
|
|
This allows deeply nested pipelines, and the possibility of "black-box" meta-elements.
|
|
|
|
Name
|
|
----
|
|
|
|
All elements are named, and while they should ideally be unique in any given pipeline, the do not have to be. The only
|
|
guaranteed unique name for an element is its complete path in the object hierarchy. Functions are provided to set and
|
|
get the name of the element. _set_name() creates a local copy of the string passed. _get_name() returns the actual
|
|
element's pointer. Therefore, the argument to _set_name() is the responsibility of the caller to free if necessary,
|
|
but the return from _get_name() is definitely not to be messed with by the caller. Accordingly, _get_name() returns an
|
|
const gchar *.
|
|
|
|
Providing a new name to an element causes it to free its internal copy of the name and make a copy of the new name.
|
|
This means that you must consider the pointer returned by _get_name() to be short-lived. If you must make use of the
|
|
name beyond the immediate scope, it is suggested that you make yourself a copy of it. If you know for a fact neither
|
|
the pointer nor its contents will change, you may retain the original pointer. If you get odd results when using the
|
|
returned string, that's the first thing to check.
|
|
|
|
|
|
Pads
|
|
----
|
|
|
|
GstPads are the property of a given GstElement. They provide the connection capability, with allowing arbitrary
|
|
structure in the graph. For any Element but a source or sink, there will be at least 2 Pads owned by the Element.
|
|
These pads are stored in a single GList within the Element. Several counters are kept in order to allow quicker
|
|
determination of the type and properties of a given Element.
|
|
|
|
Pads may be added to an element with _add_pad. Retrieval is via _get_pad(), which operates on the name of the Pad (the
|
|
unique key). This means that all Pads owned by a given Element must have unique names (FIXME we don't verify this at
|
|
_add time). A pointer to the GList of pads may be obtained with _get_pad_list. As with the element's name,
|
|
precaution must be taken with all these pointers, as they are the same pointer that the Element uses internally. One
|
|
must be especially careful not to manipulate the list of pads.
|
|
|
|
gst_element_add_pad(element,pads):
|
|
Sets the element as the parent of the pad, then adds the pad to the element's list of pads, keeping the counts
|
|
of total, src, and sink pads up to date. Emits the "new_pad" signal with the pad as argument. Fails if either
|
|
the element or pad are either NULL or not what they claim to be. Should fail if the pad already has a parent.
|
|
Should fail if the pad is already owned by the element. Should fail if there's already a pad by that name in
|
|
the the list of pads.
|
|
|
|
pad = gst_element_get_pad(element,"padname"):
|
|
Searches through the list of pads
|
|
|
|
|
|
Ghost Pads
|
|
----------
|
|
|
|
|
|
State
|
|
-----
|
|
|
|
Elements use state to determine what the are capable of doing at any given moment. The states are defined as follows:
|
|
|
|
NULL No state is held for the element
|
|
READY Devices are open
|
|
PLAYING
|
|
PAUSED
|