GstBin

GstBin — Base class and element that can contain other elements

Synopsis


#include <gst/gst.h>


                    GstBin;
                    GstBinClass;
GstElement*         gst_bin_new                         (const gchar *name);
gboolean            gst_bin_add                         (GstBin *bin,
                                                         GstElement *element);
gboolean            gst_bin_remove                      (GstBin *bin,
                                                         GstElement *element);
GstElement*         gst_bin_get_by_name                 (GstBin *bin,
                                                         const gchar *name);
GstElement*         gst_bin_get_by_name_recurse_up      (GstBin *bin,
                                                         const gchar *name);
GstElement*         gst_bin_get_by_interface            (GstBin *bin,
                                                         GType iface);
GstIterator*        gst_bin_iterate_elements            (GstBin *bin);
GstIterator*        gst_bin_iterate_recurse             (GstBin *bin);
GstIterator*        gst_bin_iterate_sinks               (GstBin *bin);
GstIterator*        gst_bin_iterate_sorted              (GstBin *bin);
GstIterator*        gst_bin_iterate_sources             (GstBin *bin);
GstIterator*        gst_bin_iterate_all_by_interface    (GstBin *bin,
                                                         GType iface);

void                gst_bin_add_many                    (GstBin *bin,
                                                         GstElement *element_1,
                                                         ...);
void                gst_bin_remove_many                 (GstBin *bin,
                                                         GstElement *element_1,
                                                         ...);
GstPad*             gst_bin_find_unconnected_pad        (GstBin *bin,
                                                         GstPadDirection direction);

enum                GstBinFlags;
#define             GST_BIN_CHILDREN                    (bin)
#define             GST_BIN_CHILDREN_COOKIE             (bin)
#define             GST_BIN_NUMCHILDREN                 (bin)


Object Hierarchy


  GObject
   +----GstObject
         +----GstElement
               +----GstBin
                     +----GstPipeline

Implemented Interfaces

GstBin implements GstChildProxy.

Properties


  "async-handling"           gboolean              : Read / Write

Signals


  "element-added"                                  : Run First
  "element-removed"                                : Run First

Description

GstBin is an element that can contain other GstElement, allowing them to be managed as a group. Pads from the child elements can be ghosted to the bin, see GstGhostPad. This makes the bin look like any other elements and enables creation of higher-level abstraction elements.

A new GstBin is created with gst_bin_new(). Use a GstPipeline instead if you want to create a toplevel bin because a normal bin doesn't have a bus or handle clock distribution of its own.

After the bin has been created you will typically add elements to it with gst_bin_add(). You can remove elements with gst_bin_remove().

An element can be retrieved from a bin with gst_bin_get_by_name(), using the elements name. gst_bin_get_by_name_recurse_up() is mainly used for internal purposes and will query the parent bins when the element is not found in the current bin.

An iterator of elements in a bin can be retrieved with gst_bin_iterate_elements(). Various other iterators exist to retrieve the elements in a bin.

gst_object_unref() is used to drop your reference to the bin.

The element-added signal is fired whenever a new element is added to the bin. Likewise the element-removed signal is fired whenever an element is removed from the bin.

Notes

A GstBin internally intercepts every GstMessage posted by its children and implements the following default behaviour for each of them:

GST_MESSAGE_EOS

This message is only posted by sinks in the PLAYING state. If all sinks posted the EOS message, this bin will post and EOS message upwards.

GST_MESSAGE_SEGMENT_START

just collected and never forwarded upwards. The messages are used to decide when all elements have completed playback of their segment.

GST_MESSAGE_SEGMENT_DONE

Is posted by GstBin when all elements that posted a SEGMENT_START have posted a SEGMENT_DONE.

GST_MESSAGE_DURATION

Is posted by an element that detected a change in the stream duration. The default bin behaviour is to clear any cached duration values so that the next duration query will perform a full duration recalculation. The duration change is posted to the application so that it can refetch the new duration with a duration query.

GST_MESSAGE_CLOCK_LOST

This message is posted by an element when it can no longer provide a clock. The default bin behaviour is to check if the lost clock was the one provided by the bin. If so and the bin is currently in the PLAYING state, the message is forwarded to the bin parent. This message is also generated when a clock provider is removed from the bin. If this message is received by the application, it should PAUSE the pipeline and set it back to PLAYING to force a new clock distribution.

GST_MESSAGE_CLOCK_PROVIDE

This message is generated when an element can provide a clock. This mostly happens when a new clock provider is added to the bin. The default behaviour of the bin is to mark the currently selected clock as dirty, which will perform a clock recalculation the next time the bin is asked to provide a clock. This message is never sent tot the application but is forwarded to the parent of the bin.

OTHERS

posted upwards.

A GstBin implements the following default behaviour for answering to a GstQuery:

GST_QUERY_DURATION

If the query has been asked before with the same format and the bin is a toplevel bin (ie. has no parent), use the cached previous value. If no previous value was cached, the query is sent to all sink elements in the bin and the MAXIMUM of all values is returned. If the bin is a toplevel bin the value is cached. If no sinks are available in the bin, the query fails.

GST_QUERY_POSITION

The query is sent to all sink elements in the bin and the MAXIMUM of all values is returned. If no sinks are available in the bin, the query fails.

OTHERS

the query is forwarded to all sink elements, the result of the first sink that answers the query successfully is returned. If no sink is in the bin, the query fails.

A GstBin will by default forward any event sent to it to all sink elements. If all the sinks return TRUE, the bin will also return TRUE, else FALSE is returned. If no sinks are in the bin, the event handler will return TRUE.

Last reviewed on 2006-04-28 (0.10.6)

Details

GstBin

typedef struct {
  /* our children, subclass are supposed to update these
   * fields to reflect their state with _iterate_*() */
  gint		 numchildren;
  GList		*children;
  guint32	 children_cookie;

  GstBus        *child_bus;
  GList         *messages;

  gboolean	 polling;
  gboolean       state_dirty;

  gboolean       clock_dirty;
  GstClock	*provided_clock;
  GstElement    *clock_provider;

  GstBinPrivate *priv;
} GstBin;

The GstBin base class. Subclasses can access these fields provided the LOCK is taken.

gint numchildren; the number of children in this bin
GList *children; the list of children in this bin
guint32 children_cookie; updated whenever children changes
GstBus *child_bus; internal bus for handling child messages
GList *messages; queued and cached messages
gboolean polling; the bin is currently calculating its state
gboolean state_dirty; the bin needs to recalculate its state (deprecated)
gboolean clock_dirty; the bin needs to select a new clock
GstClock *provided_clock; the last clock selected
GstElement *clock_provider; the element that provided provided_clock
GstBinPrivate *priv;

GstBinClass

typedef struct {
  GstElementClass parent_class;

  /* virtual methods for subclasses */
  gboolean	(*add_element)		(GstBin *bin, GstElement *element);
  gboolean	(*remove_element)	(GstBin *bin, GstElement *element);

  void		(*handle_message)	(GstBin *bin, GstMessage *message);
} GstBinClass;

Subclasses can override the add_element and remove_element to update the list of children in the bin.

The handle_message method can be overriden to implement custom message handling.

GstElementClass parent_class; bin parent class
add_element () method to add an element to a bin
remove_element () method to remove an element from a bin
handle_message () method to handle a message from the children

gst_bin_new ()

GstElement*         gst_bin_new                         (const gchar *name);

Creates a new bin with the given name.

name : the name of the new bin
Returns : a new GstBin

gst_bin_add ()

gboolean            gst_bin_add                         (GstBin *bin,
                                                         GstElement *element);

Adds the given element to the bin. Sets the element's parent, and thus takes ownership of the element. An element can only be added to one bin.

If the element's pads are linked to other pads, the pads will be unlinked before the element is added to the bin.

MT safe.

bin : a GstBin
element : the GstElement to add
Returns : TRUE if the element could be added, FALSE if the bin does not want to accept the element.

gst_bin_remove ()

gboolean            gst_bin_remove                      (GstBin *bin,
                                                         GstElement *element);

Removes the element from the bin, unparenting it as well. Unparenting the element means that the element will be dereferenced, so if the bin holds the only reference to the element, the element will be freed in the process of removing it from the bin. If you want the element to still exist after removing, you need to call gst_object_ref() before removing it from the bin.

If the element's pads are linked to other pads, the pads will be unlinked before the element is removed from the bin.

MT safe.

bin : a GstBin
element : the GstElement to remove
Returns : TRUE if the element could be removed, FALSE if the bin does not want to remove the element.

gst_bin_get_by_name ()

GstElement*         gst_bin_get_by_name                 (GstBin *bin,
                                                         const gchar *name);

Gets the element with the given name from a bin. This function recurses into child bins.

Returns NULL if no element with the given name is found in the bin.

MT safe. Caller owns returned reference.

bin : a GstBin
name : the element name to search for
Returns : the GstElement with the given name, or NULL

gst_bin_get_by_name_recurse_up ()

GstElement*         gst_bin_get_by_name_recurse_up      (GstBin *bin,
                                                         const gchar *name);

Gets the element with the given name from this bin. If the element is not found, a recursion is performed on the parent bin.

Returns NULL if: - no element with the given name is found in the bin

MT safe. Caller owns returned reference.

bin : a GstBin
name : the element name to search for
Returns : the GstElement with the given name, or NULL

gst_bin_get_by_interface ()

GstElement*         gst_bin_get_by_interface            (GstBin *bin,
                                                         GType iface);

Looks for an element inside the bin that implements the given interface. If such an element is found, it returns the element. You can cast this element to the given interface afterwards. If you want all elements that implement the interface, use gst_bin_iterate_all_by_interface(). This function recurses into child bins.

MT safe. Caller owns returned reference.

bin : a GstBin
iface : the GType of an interface
Returns : A GstElement inside the bin implementing the interface

gst_bin_iterate_elements ()

GstIterator*        gst_bin_iterate_elements            (GstBin *bin);

Gets an iterator for the elements in this bin.

Each element yielded by the iterator will have its refcount increased, so unref after use.

MT safe. Caller owns returned value.

bin : a GstBin
Returns : a GstIterator of GstElement, or NULL

gst_bin_iterate_recurse ()

GstIterator*        gst_bin_iterate_recurse             (GstBin *bin);

Gets an iterator for the elements in this bin. This iterator recurses into GstBin children.

Each element yielded by the iterator will have its refcount increased, so unref after use.

MT safe. Caller owns returned value.

bin : a GstBin
Returns : a GstIterator of GstElement, or NULL

gst_bin_iterate_sinks ()

GstIterator*        gst_bin_iterate_sinks               (GstBin *bin);

Gets an iterator for all elements in the bin that have the GST_ELEMENT_IS_SINK flag set.

Each element yielded by the iterator will have its refcount increased, so unref after use.

MT safe. Caller owns returned value.

bin : a GstBin
Returns : a GstIterator of GstElement, or NULL

gst_bin_iterate_sorted ()

GstIterator*        gst_bin_iterate_sorted              (GstBin *bin);

Gets an iterator for the elements in this bin in topologically sorted order. This means that the elements are returned from the most downstream elements (sinks) to the sources.

This function is used internally to perform the state changes of the bin elements.

Each element yielded by the iterator will have its refcount increased, so unref after use.

MT safe. Caller owns returned value.

bin : a GstBin
Returns : a GstIterator of GstElement, or NULL

gst_bin_iterate_sources ()

GstIterator*        gst_bin_iterate_sources             (GstBin *bin);

Gets an iterator for all elements in the bin that have no sinkpads and have the GST_ELEMENT_IS_SINK flag unset.

Each element yielded by the iterator will have its refcount increased, so unref after use.

MT safe. Caller owns returned value.

bin : a GstBin
Returns : a GstIterator of GstElement, or NULL

gst_bin_iterate_all_by_interface ()

GstIterator*        gst_bin_iterate_all_by_interface    (GstBin *bin,
                                                         GType iface);

Looks for all elements inside the bin that implements the given interface. You can safely cast all returned elements to the given interface. The function recurses inside child bins. The iterator will yield a series of GstElement that should be unreffed after use.

Each element yielded by the iterator will have its refcount increased, so unref after use.

MT safe. Caller owns returned value.

bin : a GstBin
iface : the GType of an interface
Returns : a GstIterator of GstElement for all elements in the bin implementing the given interface, or NULL

gst_bin_add_many ()

void                gst_bin_add_many                    (GstBin *bin,
                                                         GstElement *element_1,
                                                         ...);

Adds a NULL-terminated list of elements to a bin. This function is equivalent to calling gst_bin_add() for each member of the list.

bin : a GstBin
element_1 : the GstElement element to add to the bin
... : additional elements to add to the bin

gst_bin_remove_many ()

void                gst_bin_remove_many                 (GstBin *bin,
                                                         GstElement *element_1,
                                                         ...);

Remove a list of elements from a bin. This function is equivalent to calling gst_bin_remove() with each member of the list.

bin : a GstBin
element_1 : the first GstElement to remove from the bin
... : NULL-terminated list of elements to remove from the bin

gst_bin_find_unconnected_pad ()

GstPad*             gst_bin_find_unconnected_pad        (GstBin *bin,
                                                         GstPadDirection direction);

Recursively looks for elements with an unconnected pad of the given direction within the specified bin and returns an unconnected pad if one is found, or NULL otherwise. If a pad is found, the caller owns a reference to it and should use gst_object_unref() on the pad when it is not needed any longer.

bin : bin in which to look for elements with unconnected pads
direction : whether to look for an unconnected source or sink pad
Returns : unconnected pad of the given direction, or NULL.

Since 0.10.3


enum GstBinFlags

typedef enum {
  /* padding */
  GST_BIN_FLAG_LAST		= (GST_ELEMENT_FLAG_LAST << 5)
} GstBinFlags;

GstBinFlags are a set of flags specific to bins. Most are set/used internally. They can be checked using the GST_OBJECT_FLAG_IS_SET() macro, and (un)set using GST_OBJECT_FLAG_SET() and GST_OBJECT_FLAG_UNSET().

GST_BIN_FLAG_LAST the last enum in the series of flags for bins. Derived classes can use this as first value in a list of flags.

GST_BIN_CHILDREN()

#define GST_BIN_CHILDREN(bin)		(GST_BIN_CAST(bin)->children)

Gets the list with children in a bin.

bin : a GstBin

GST_BIN_CHILDREN_COOKIE()

#define GST_BIN_CHILDREN_COOKIE(bin)	(GST_BIN_CAST(bin)->children_cookie)

Gets the children cookie that watches the children list.

bin : a GstBin

GST_BIN_NUMCHILDREN()

#define GST_BIN_NUMCHILDREN(bin)	(GST_BIN_CAST(bin)->numchildren)

Gets the number of children in a bin.

bin : a GstBin

Property Details

The "async-handling" property

  "async-handling"           gboolean              : Read / Write

If set to TRUE, the bin will handle asynchronous state changes. This should be used only if the bin subclass is modifying the state of its childs on its own.

Default value: FALSE

Since 0.10.13

Signal Details

The "element-added" signal

void                user_function                      (GstBin     *bin,
                                                        GstElement *element,
                                                        gpointer    user_data)      : Run First

Will be emitted after the element was added to the bin.

bin : the GstBin
element : the GstElement that was added to the bin
user_data : user data set when the signal handler was connected.

The "element-removed" signal

void                user_function                      (GstBin     *bin,
                                                        GstElement *element,
                                                        gpointer    user_data)      : Run First

Will be emitted after the element was removed from the bin.

bin : the GstBin
element : the GstElement that was removed from the bin
user_data : user data set when the signal handler was connected.