GstContext

GstContext — Lightweight objects to represent element contexts

Functions

Types and Values

Object Hierarchy

    GBoxed
    ╰── GstContext

Includes

#include <gst/gst.h>

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:

  1. Check if the element already has a context

  2. Query downstream with GST_QUERY_CONTEXT for the context

  3. Query upstream with GST_QUERY_CONTEXT for the context

  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

  5. 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.

Functions

gst_context_new ()

GstContext *
gst_context_new (const gchar *context_type,
                 gboolean persistent);

Create a new context.

Parameters

context_type

Context type

 

persistent

Persistent context

 

Returns

The new context.

[transfer full]

Since 1.2


gst_context_ref ()

GstContext *
gst_context_ref (GstContext *context);

Convenience macro to increase the reference count of the context.

Parameters

context

the context to ref

 

Returns

context (for convenience when doing assignments)


gst_context_unref ()

void
gst_context_unref (GstContext *context);

Convenience macro to decrease the reference count of the context, possibly freeing it.

Parameters

context

the context to unref

 

gst_context_copy ()

GstContext *
gst_context_copy (const GstContext *context);

Creates a copy of the context. Returns a copy of the context.

Parameters

context

the context to copy

 

Returns

a new copy of context .

MT safe.

[transfer full]


gst_context_get_context_type ()

const gchar *
gst_context_get_context_type (const GstContext *context);

Get the type of context .

Parameters

context

The GstContext.

 

Returns

The type of the 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 .

Parameters

context

The GstContext.

 

context_type

Context type to check.

 

Returns

TRUE 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.

Parameters

context

The GstContext.

 

Returns

TRUE if the 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.

Parameters

context

The GstContext.

 

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.

Parameters

context

The GstContext.

 

Returns

The structure of the context. The structure is still owned by the event, which means that you should not free it and that the pointer becomes invalid when you free the event. 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.

Parameters

context

the context to make writable.

[transfer full]

Returns

a context (possibly a duplicate) that is writable.

MT safe.

[transfer full]


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.

Parameters

context

a GstContext

 

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 old_context .

[allow-none][transfer none]

Returns

TRUE if new_context was different from old_context

Types and Values

GstContext

typedef struct _GstContext GstContext;

See Also

GstMiniObject, GstElement