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docs: add the start of a design document for controller

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Stefan Sauer 2011-12-25 20:49:41 +01:00
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docs/design/part-controller.txt Normal file
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Controller
----------
The controller subsystem allows to automate element property changes. It works
so that all parameter changes are time based and elements request property
updates at processing time.
Element view
~~~~~~~~~~~~
Elements don't need to do much. They need to:
- mark object properties that can be changed while processing with
GST_PARAM_CONTROLLABLE
- call gst_object_sync_values (self, timestamp) in the processing function
before accessing the parameters.
Application view
~~~~~~~~~~~~~~~~
Application need to setup the property automation. For that they need to create
a GstControlSource and attach it to a property using GstControlBinding. Various
control-sources and control-bindings exists. All control sources produce control
value sequences in the form of gdouble values. The control bindings map them to
the value range and type of the bound property.