Context

GstContext is a container object used to store contexts like a device context, a display server connection and similar concepts that should be shared between multiple elements.

Applications can set a context on a complete pipeline by using gst_element_set_context(), which will then be propagated to all child elements. Elements can handle these in GstElement::set_context() and merge them with the context information they already have.

When an element needs a context it will do the following actions in this order until one step succeeds: 1) Check if the element already has a context 2) Query downstream with GST_QUERY_CONTEXT for the context 2) Query upstream with GST_QUERY_CONTEXT for the context 3) 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 4) Create a context by itself and post a GST_MESSAGE_HAVE_CONTEXT message on the bus.

Bins will catch GST_MESSAGE_NEED_CONTEXT messages and will set any previously known context on the element that asks for it if possible. Otherwise the application should provide one if it can.

class Context {

protected

GstContext* gstContext;

GstContext* getContextStruct();

void* getStruct();

this(GstContext* gstContext);

this(string contextType, int persistent);

Context doref();

void unref();

Context copy();

string getContextType();

int hasContextType(string contextType);

int isPersistent();

Structure getStructure();

Structure writableStructure();

static int replace(Context oldContext, Context newContext);

}

Constructors

this this(GstContext* gstContext): Sets our main struct and passes it to the parent class
this this(string contextType, int persistent): Create a new context. Since 1.2

Members

Functions

copy Context copy(): Creates a copy of the context. Returns a copy of the context.
doref Context doref(): Convenience macro to increase the reference count of the context.
getContextStruct GstContext* getContextStruct(): Get the main Gtk struct
getContextType string getContextType(): Get the type of context. Since 1.2
getStruct void* getStruct(): the main Gtk struct as a void*
getStructure Structure getStructure(): Access the structure of the context. Since 1.2
hasContextType int hasContextType(string contextType): Checks if context has context_type. Since 1.2
isPersistent int isPersistent(): Check if context is persistent. Since 1.2
unref void unref(): Convenience macro to decrease the reference count of the context, possibly freeing it.
writableStructure Structure writableStructure(): Get a writable version of the structure. Since 1.2

Static functions

replace int replace(Context oldContext, Context newContext): Modifies a pointer to a GstContext to point to a different GstContext. The modification is done atomically (so this is useful for ensuring thread safety in some cases), and the reference counts are updated appropriately (the old context is unreffed, the new one is reffed). Either new_context or the GstContext pointed to by old_context may be NULL.

Variables

gstContext GstContext* gstContext;: the main Gtk struct