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93 lines
2.4 KiB
Text
93 lines
2.4 KiB
Text
SOMEWHAT OUTDATED
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-----------------
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We describe how the plugin system works.
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Plugins
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-------
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plugins are basically shared libraries with a plugin_init
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function.
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they provide the GStreamer core library with the following
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information:
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- element factories
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- type factories
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- metadata factories?
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ElementFactory
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--------------
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element factories provide the core library with elements (duh)
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an element factory has the following information:
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- a unique name for the element factory
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- strings describing the element (name, desciption, copyright,...)
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- a description of the media types it accepts (as capabilities)
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- a description of the media types it outputs (as capabilities)
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TypeFactory
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-----------
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has the following properties:
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- a mime type
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- file extensions that may provide a hint for this type
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- a function to detect this type
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- a string to detect this type (file(1) like)
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XML registry
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------------
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The complete plugin tree will be exported into an XML description so
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that the definitions of the factories can be obtained without having
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to load and plugin_init the plugins.
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Loading of plugins
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------------------
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at some point, the plugin will need to be read into memory before
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any elements it provides can be used. the XML description of the
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loaded plugin will need to be updated.
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We will have the following methods for (implicitly) loading plugins:
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gst_plugin_load_all()
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remove the complete XML tree and read all the plugins in the
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paths. The plugin_init method will be called and the XML tree
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will be rebuild in memory.
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gst_plugin_load (name)
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The plugin will be located in the tree and if it already loaded, the
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function returns. If it is not loaded, the XML entry is removed and
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the plugin is loaded. The plugin_init is called so that the XML tree
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is reconstructed.
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gst_elementfactory_create (factory, name);
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The plugin providing the element will be located, if the plugin is
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already loaded, an element with the given name is created.
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if the plugin is not loaded, gst_plugin_load is called.
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the loaded factory is located again and the element is created.
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The typefind function is called
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When the plugin description is read from the XML file, the typefind
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function is hooked up to a dummy typefind function. The dummy typefind
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function will locate the plugin it belongs to and call gst_plugin_load.
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after the loading of the plugin, the real typefind function is called.
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