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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
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<title>GstContext: GStreamer 1.0 Core Reference Manual</title>
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<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
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Top  | 
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                  Description  | 
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                  Object Hierarchy
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Home
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Up
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Prev
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Next
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GstContext
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GstContext — Lightweight objects to represent element contexts
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Functions
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GstContext *
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gst_context_new ()
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GstContext *
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gst_context_ref ()
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void
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gst_context_unref ()
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GstContext *
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gst_context_copy ()
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const gchar *
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gst_context_get_context_type ()
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gboolean
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gst_context_has_context_type ()
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gboolean
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gst_context_is_persistent ()
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const GstStructure *
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gst_context_get_structure ()
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GstStructure *
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gst_context_writable_structure ()
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#define
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gst_context_make_writable()
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#define
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gst_context_is_writable()
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gboolean
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gst_context_replace ()
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Types and Values
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GstContext
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Object Hierarchy
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    GBoxed
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    ╰── GstContext
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Includes
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#include <gst/gst.h>
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Description
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GstContext is a container object used to store contexts like a device
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context, a display server connection and similar concepts that should
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be shared between multiple elements.
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Applications can set a context on a complete pipeline by using
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gst_element_set_context(), which will then be propagated to all
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child elements. Elements can handle these in GstElementClass.set_context()
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and merge them with the context information they already have.
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When an element needs a context it will do the following actions in this
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order until one step succeeds:
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  1. Check if the element already has a context
    		2.
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  2. Query downstream with GST_QUERY_CONTEXT for the context
    		3.
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  3. Query upstream with GST_QUERY_CONTEXT for the context
    		4.
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  4. Post a GST_MESSAGE_NEED_CONTEXT message on the bus with the required
    		5.
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    context types and afterwards check if a usable context was set now
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  5. Create a context by itself and post a GST_MESSAGE_HAVE_CONTEXT message
    		6.
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    on the bus.
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    Bins will catch GST_MESSAGE_NEED_CONTEXT messages and will set any previously
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    known context on the element that asks for it if possible. Otherwise the
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    application should provide one if it can.
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    GstContexts can be persistent.
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    A persistent GstContext is kept in elements when they reach
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    GST_STATE_NULL, non-persistent ones will be removed.
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    Also, a non-persistent context won't override a previous persistent
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    context set to an element.
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    Functions
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    gst_context_new ()
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    GstContext *
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    gst_context_new (const gchar *context_type,
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                     gboolean persistent);
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    Create a new context.
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    Parameters
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    context_type
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    Context type
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    persistent
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    Persistent context
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    Returns
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    The new context.
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    [transfer full]
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    Since: 1.2
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    gst_context_ref ()
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    GstContext *
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    gst_context_ref (GstContext *context);
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    Convenience macro to increase the reference count of the context.
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    Parameters
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    context
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    the context to ref
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    Returns
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     context
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    (for convenience when doing assignments)
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    gst_context_unref ()
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    void
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    gst_context_unref (GstContext *context);
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    Convenience macro to decrease the reference count of the context, possibly
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    freeing it.
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    Parameters
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    context
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    the context to unref
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    gst_context_copy ()
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    GstContext *
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    gst_context_copy (const GstContext *context);
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    Creates a copy of the context. Returns a copy of the context.
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    Parameters
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    context
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    the context to copy
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    Returns
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    a new copy of context
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    .
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    MT safe.
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    [transfer full]
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    gst_context_get_context_type ()
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    const gchar *
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    gst_context_get_context_type (const GstContext *context);
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    Get the type of context
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    .
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    Parameters
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    context
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    The GstContext.
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    Returns
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     The type of the context.
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    Since: 1.2
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    gst_context_has_context_type ()
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    gboolean
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    gst_context_has_context_type (const GstContext *context,
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                                  const gchar *context_type);
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    Checks if context
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     has context_type
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    .
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    Parameters
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    context
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    The GstContext.
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    context_type
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    Context type to check.
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    Returns
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     TRUE if context
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    has context_type
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    .
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    Since: 1.2
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    gst_context_is_persistent ()
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    gboolean
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    gst_context_is_persistent (const GstContext *context);
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    Check if context
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     is persistent.
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    Parameters
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    context
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    The GstContext.
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    Returns
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     TRUE if the context is persistent.
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    Since: 1.2
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    gst_context_get_structure ()
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    const GstStructure *
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    gst_context_get_structure (const GstContext *context);
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    Access the structure of the context.
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    Parameters
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    context
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    The GstContext.
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    Returns
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    The structure of the context. The structure is
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    still owned by the context, which means that you should not modify it,
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    free it and that the pointer becomes invalid when you free the context.
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    [transfer none]
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    Since: 1.2
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    gst_context_writable_structure ()
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    GstStructure *
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    gst_context_writable_structure (GstContext *context);
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    Get a writable version of the structure.
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    Parameters
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    context
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    The GstContext.
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    Returns
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     The structure of the context. The structure is still
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    owned by the context, which means that you should not free it and
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    that the pointer becomes invalid when you free the context.
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    This function checks if context
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    is writable.
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    Since: 1.2
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    gst_context_make_writable()
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    #define         gst_context_make_writable(context)  GST_CONTEXT_CAST (gst_mini_object_make_writable (GST_MINI_OBJECT_CAST (context)))
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    Checks if a context is writable. If not, a writable copy is made and
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    returned.
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    Parameters
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    context
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    the context to make writable.
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    [transfer full]
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    Returns
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    a context (possibly a duplicate) that is writable.
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    MT safe.
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    [transfer full]
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    gst_context_is_writable()
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    #define         gst_context_is_writable(context)     gst_mini_object_is_writable (GST_MINI_OBJECT_CAST (context))
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    Tests if you can safely write into a context's structure or validly
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    modify the seqnum and timestamp fields.
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    Parameters
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    context
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    a GstContext
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    gst_context_replace ()
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    gboolean
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    gst_context_replace (GstContext **old_context,
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                         GstContext *new_context);
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    Modifies a pointer to a GstContext to point to a different GstContext. The
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    modification is done atomically (so this is useful for ensuring thread safety
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    in some cases), and the reference counts are updated appropriately (the old
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    context is unreffed, the new one is reffed).
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    Either new_context
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     or the GstContext pointed to by old_context
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     may be NULL.
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    Parameters
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    old_context
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    pointer to a pointer to a GstContext
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    to be replaced.
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    [inout][transfer full]
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    new_context
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    pointer to a GstContext that will
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    replace the context pointed to by old_context
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    .
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    [allow-none][transfer none]
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    Returns
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     TRUE if new_context
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    was different from old_context
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    Types and Values
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    GstContext
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    typedef struct _GstContext GstContext;
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    See Also
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    GstMiniObject, GstElement
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    Generated by GTK-Doc V1.27
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    </body>
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    </html>

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