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135 lines
4.1 KiB
Text
135 lines
4.1 KiB
Text
Autoplugger V2
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==============
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The current autoplugger as described in autoplug1 has some
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serious shortcomings:
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- it is embedded in GstPipeline and cannot be used with a
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generic interface. A lot of complexity is inside the
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pipeline, more specifically the creation of threads and
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subbins and the pad connections.
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- it is not (easily) pluggable.
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1) definition
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-------------
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We want to define a pluggable framework for autoplugging this
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includes:
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- autoplugging algorithms can be added and removed at run time.
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- autoplugging algorithms can be defined by plugins.
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The autoplugger is build to handle simple media playback but
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could also be used to create more complex pipelines.
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The main focus will be on creating an element (can be a bin)
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that has *one* input pad and *one or more* output pads.
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It must be possible for a user app to insert its own elements in
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the autogenerated element.
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The autoplugger will be an interface to the low level plugin
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system based on the functional requirements of the user app.
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the app will for example request an object that can convert
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media type X to media type Y, the user app is not interested in
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any intermediate steps to accomplish this conversion.
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2) the API
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----------
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The API for the user apps should be no more then this:
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GstElement* gst_autoplug_caps_list (GstAutoplug *autoplug,
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GList *incaps,
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GList *outcaps, ...);
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autoplug is a reference to the autoplug implementation
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incaps is a GList of GstCaps* for the source pad, the last set
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of arguments is a va_list of destination caps lists.
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A handle to the autoplugger implementation can be obtained
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with
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GList* gst_autoplugfactory_get_list (void);
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which will return a GList* of autopluggers.
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GstAutoplug* gst_autoplugfactory_make ("name");
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or
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GstAutoplug* gst_autoplugfactory_create (GstAutoplugFactory *autoplug);
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is used to get an autoplugger.
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3) the plugins API
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------------------
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plugins can add their own autoplugger implementation by
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subclassing an abstract autoplugger class and implementing/
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overriding various methods.
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the autoplugger can be registered with:
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gst_plugin_add_autoplugger (GstPlugin *plugin,
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GstAutoplugFactory *autoplug);
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This will allow us to only load the autoplugger when needed.
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4) implementation
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-----------------
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We will implement two autopluggers:
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- a static autoplugger. This autoplugger recursively adds
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elements to the target element until all of the possible
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pads are connected to something. The static autoplugger
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only operates on padtemplates and ALWAYS pads. The pipeline
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is not started before all elements are connected, hence
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the 'static' autoplugger. This autoplugger will be a rework
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of the current autoplugger.
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- a dynamic autoplugger. This autoplugger configures the
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pipeline at runtime based on the pad capabilities when they
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become available. this allows for more fine grained
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autoplugging than can be achieved with the static one because
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it can be based on the actual media stream you are handling.
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the autopluggers will be implemented in their separate plugins,
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outside of the core libraries and are therefore optional.
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5) the autoplugger object
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-------------------------
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the autoplugger object will be an abstract class with the following
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properties:
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- name, description, more text to identify the autoplugger.
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- a class method autoplug_caps_list that has to be implemented by
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the real autoplugger.
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optionally, the core autoplugger code can provide convenience
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functions to implement custom autopluggers. The shortest path
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algorithm with pluggable weighting and list functions come to
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mind.
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signals will be added to the autoplugger so that user apps can
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modify the constructed pipeline by adding extra objects.
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A possible use case would be to let gstmediaplay perform an
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autoplug on the media stream and insert a custom sound/video
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effect in the pipeline when an appropriate element is created.
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the "new_object" signal will be fired by the autoplugger whenever
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a new object has been created. This signal can be caught by the
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user app to perform an introspection on the newly created object.
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