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Functions
| GstContext * | gst_context_new () |
| GstContext * | gst_context_ref () |
| void | gst_context_unref () |
| GstContext * | gst_context_copy () |
| const gchar * | gst_context_get_context_type () |
| gboolean | gst_context_has_context_type () |
| gboolean | gst_context_is_persistent () |
| const GstStructure * | gst_context_get_structure () |
| GstStructure * | gst_context_writable_structure () |
| #define | gst_context_make_writable() |
| #define | gst_context_is_writable() |
| gboolean | gst_context_replace () |
Description
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 GstElementClass.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:
Check if the element already has a context
Query downstream with GST_QUERY_CONTEXT for the context
Query upstream with GST_QUERY_CONTEXT for the context
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
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.
GstContexts can be persistent.
A persistent GstContext is kept in elements when they reach
GST_STATE_NULL, non-persistent ones will be removed.
Also, a non-persistent context won't override a previous persistent
context set to an element.
Functions
gst_context_new ()
GstContext * gst_context_new (const gchar *context_type,gboolean persistent);
Create a new context.
Since: 1.2
gst_context_ref ()
GstContext *
gst_context_ref (GstContext *context);
Convenience macro to increase the reference count of the context.
gst_context_unref ()
void
gst_context_unref (GstContext *context);
Convenience macro to decrease the reference count of the context, possibly freeing it.
gst_context_copy ()
GstContext *
gst_context_copy (const GstContext *context);
Creates a copy of the context. Returns a copy of the context.
gst_context_get_context_type ()
const gchar *
gst_context_get_context_type (const GstContext *context);
Get the type of context
.
Since: 1.2
gst_context_has_context_type ()
gboolean gst_context_has_context_type (const GstContext *context,const gchar *context_type);
Checks if context
has context_type
.
Since: 1.2
gst_context_is_persistent ()
gboolean
gst_context_is_persistent (const GstContext *context);
Check if context
is persistent.
Since: 1.2
gst_context_get_structure ()
const GstStructure *
gst_context_get_structure (const GstContext *context);
Access the structure of the context.
Returns
The structure of the context. The structure is still owned by the context, which means that you should not modify it, free it and that the pointer becomes invalid when you free the context.
[transfer none]
Since: 1.2
gst_context_writable_structure ()
GstStructure *
gst_context_writable_structure (GstContext *context);
Get a writable version of the structure.
Returns
The structure of the context. The structure is still
owned by the context, which means that you should not free it and
that the pointer becomes invalid when you free the context.
This function checks if context
is writable.
Since: 1.2
gst_context_make_writable()
#define gst_context_make_writable(context) GST_CONTEXT_CAST (gst_mini_object_make_writable (GST_MINI_OBJECT_CAST (context)))
Checks if a context is writable. If not, a writable copy is made and returned.
gst_context_is_writable()
#define gst_context_is_writable(context) gst_mini_object_is_writable (GST_MINI_OBJECT_CAST (context))
Tests if you can safely write into a context's structure or validly modify the seqnum and timestamp fields.
gst_context_replace ()
gboolean gst_context_replace (GstContext **old_context,GstContext *new_context);
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.
Parameters
old_context |
pointer to a pointer to a GstContext to be replaced. |
[inout][transfer full] |
new_context |
pointer to a GstContext that will
replace the context pointed to by |
[allow-none][transfer none] |