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69 lines
2.7 KiB
Text
69 lines
2.7 KiB
Text
GstElement
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----------
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The Element is the most important object in the entire GStreamer system, as it
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defines the structure of the pipeline. Elements include sources, filters,
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sinks, and containers (Bins). They may be an intrinsic part of the core
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GStreamer library, or may be loaded from a plugin. In some cases they're even
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fabricated from completely different systems (see the LADSPA plugin). They
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are generally created from a GstElementFactory, which will be covered in
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another chapter, but for the intrinsic types they can be created with specific
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functions.
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Elements contains GstPads (also covered in another chapter), which are
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subsequently used to connect the Elements together to form a pipeline capable
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of passing and processing data. They have a parent, which must be another
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Element. This allows deeply nested pipelines, and the possibility of
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"black-box" meta-elements.
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Name
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~~~~
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All elements are named, and while they should ideally be unique in any given
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pipeline, they do not have to be. The only guaranteed unique name for an
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element is its complete path in the object hierarchy. In other words, an
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element's name is unique inside its parent. (This follows from GstObject's
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name explanation)
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This uniqueness is guaranteed through all functions where either parentage
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or name of an element is changed.
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Pads
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~~~~
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GstPads are the property of a given GstElement. They provide the connection
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capability, with allowing arbitrary structure in the graph. For any Element
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but a source or sink, there will be at least 2 Pads owned by the Element.
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These pads are stored in a single GList within the Element. Several counters
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are kept in order to allow quicker determination of the type and properties of
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a given Element.
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Pads may be added to an element with _add_pad. Retrieval is via _get_pad(),
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which operates on the name of the Pad (the unique key). This means that all
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Pads owned by a given Element must have unique names.
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A pointer to the GList of pads may be obtained with _iterate_pads.
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gst_element_add_pad(element,pads):
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Sets the element as the parent of the pad, then adds the pad to the
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element's list of pads, keeping the counts of total, src, and sink pads
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up to date. Emits the "new_pad" signal with the pad as argument.
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Fails if either the element or pad are either NULL or not what they
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claim to be. Should fail if the pad already has a parent. Should fail
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if the pad is already owned by the element. Should fail if there's
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already a pad by that name in the list of pads.
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pad = gst_element_get_pad(element,"padname"):
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Searches through the list of pads
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Ghost Pads
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~~~~~~~~~~
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More info in part-gstghostpad.txt.
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State
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~~~~~
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An element has a state. More info in part-states.txt.
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