|GstContext is a container object, containing a type string and a
|generic GstStructure. It is used to store and propagate context
|information in a pipeline, like device handles, display server
|connections and other information that should be shared between
|multiple elements in a pipeline.
|For sharing context objects and distributing them between application
|and elements in a pipeline, there are downstream queries, upstream
|queries, messages and functions to set a context on a complete pipeline.
|Context type names should be unique and be put in appropriate namespaces,
|to prevent name conflicts, e.g. "gst.egl.EGLDisplay". Only one specific
|type is allowed per context type name.
|Elements that need a specific context for their operation would
|do the following steps until one succeeds:
| 1) Check if the element already has a context of the specific type,
| i.e. it was previously set via gst_element_set_context().
| 2) Query downstream with GST_QUERY_CONTEXT for the context and check if
| downstream already has a context of the specific type
| 3) Query upstream with GST_QUERY_CONTEXT for the context and check if
| upstream already has a context of the specific type
| 4) Post a GST_MESSAGE_NEED_CONTEXT message on the bus with the required
| context types and afterwards check if a usable context was set now
| as in 1). The message could be handled by the parent bins of the
| element and the application.
| 4) Create a context by itself and post a GST_MESSAGE_HAVE_CONTEXT message
| on the bus.
|Bins will propagate any context that is set on them to their child elements via
|gst_element_set_context(). Even to elements added after a given context has
|Bins can handle the GST_MESSAGE_NEED_CONTEXT message, can filter both
|messages and can also set different contexts for different pipeline parts.
|Applications can set a specific context on a pipeline or elements inside
|a pipeline with gst_element_set_context().
|If an element inside the pipeline needs a specific context, it will post
|a GST_MESSAGE_NEED_CONTEXT message on the bus. The application can now
|create a context of the requested type or pass an already existing context
|to the element (or to the complete pipeline).
|Whenever an element creates a context internally it will post a
|GST_MESSAGE_HAVE_CONTEXT message on the bus. Bins will cache these
|contexts and pass them to any future element that requests them.