mirror of
https://gitlab.freedesktop.org/gstreamer/gstreamer.git
synced 2024-12-21 15:56:42 +00:00
59 lines
2.7 KiB
Markdown
59 lines
2.7 KiB
Markdown
# GstElement
|
||
|
||
The `GstElement` 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). Elements 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 contain `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 their names 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 the parentage or name of an element is changed.
|
||
|
||
## Pads
|
||
|
||
`GstPads` are the property of a given `GstElement`. They provide the
|
||
connection capability allowing arbitrary structure in the graph.
|
||
Every `GstElement` (with the exception of sources and sinks) have at
|
||
least 2 `GstPad`s. 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 done via
|
||
`_get_static_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. A pointer to the `GList` of pads may be obtained with
|
||
`_iterate_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
|
||
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 list of pads.
|
||
|
||
`pad = gst_element_get_pad(element, "padname")`: Searches through the
|
||
list of pads
|
||
|
||
## Ghost Pads
|
||
|
||
More info in [ghostpad](additional/design/gstghostpad.md).
|
||
|
||
## State
|
||
|
||
An element has a state. More info in [state](additional/design/states.md).
|