mirror of
https://gitlab.freedesktop.org/gstreamer/gstreamer.git
synced 2024-11-27 20:21:24 +00:00
326d36b8d8
Original commit message from CVS: Added state change code. Added/updated docs. Added sink base class, make fakesink extend the base class. Small cleanups in GstPipeline.
78 lines
3.1 KiB
Text
78 lines
3.1 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, they do not have to be. The only guaranteed unique name for an
|
|
element is its complete path in the object hierarchy. In other words, an
|
|
element's name is unique inside its parent. (This follows from GstObject's
|
|
name explanation)
|
|
|
|
This uniqueness is guaranteed through all functions where either parentage
|
|
or name of an element is changed.
|
|
|
|
|
|
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
|