struct GstElement

struct GstElement {
  GRecMutex             state_lock;

  /* element state */
  GCond                 state_cond;
  guint32               state_cookie;
  GstState              target_state;
  GstState              current_state;
  GstState              next_state;
  GstState              pending_state;
  GstStateChangeReturn  last_return;

  GstBus               *bus;

  /* allocated clock */
  GstClock             *clock;
  GstClockTimeDiff      base_time; /* NULL/READY: 0 - PAUSED: current time - PLAYING: difference to clock */
  GstClockTime          start_time;

  /* element pads, these lists can only be iterated while holding
   * the LOCK or checking the cookie after each LOCK. */
  guint16               numpads;
  GList                *pads;
  guint16               numsrcpads;
  GList                *srcpads;
  guint16               numsinkpads;
  GList                *sinkpads;
  guint32               pads_cookie;
};

GStreamer element abstract base class.

struct GstElementClass

struct GstElementClass {
  GstObjectClass         parent_class;

  /* the element metadata */
  gpointer		 metadata;

  /* factory that the element was created from */
  GstElementFactory     *elementfactory;

  /* templates for our pads */
  GList                 *padtemplates;
  gint                   numpadtemplates;
  guint32                pad_templ_cookie;

  /* virtual methods for subclasses */

  /* request/release pads */
  GstPad*               (*request_new_pad)      (GstElement *element, GstPadTemplate *templ,
                                                 const gchar* name, const GstCaps *caps);
  void                  (*release_pad)          (GstElement *element, GstPad *pad);

  /* state changes */
  GstStateChangeReturn (*get_state)             (GstElement * element, GstState * state,
                                                 GstState * pending, GstClockTime timeout);
  GstStateChangeReturn (*set_state)             (GstElement *element, GstState state);
  GstStateChangeReturn (*change_state)          (GstElement *element, GstStateChange transition);
  void                 (*state_changed)         (GstElement *element, GstState oldstate,
                                                 GstState newstate, GstState pending);

  /* bus */
  void                  (*set_bus)              (GstElement * element, GstBus * bus);

  /* set/get clocks */
  GstClock*             (*provide_clock)        (GstElement *element);
  gboolean              (*set_clock)            (GstElement *element, GstClock *clock);

  /* query functions */
  gboolean              (*send_event)           (GstElement *element, GstEvent *event);

  gboolean              (*query)                (GstElement *element, GstQuery *query);

  gboolean              (*post_message)         (GstElement *element, GstMessage *message);

  void                  (*set_context)          (GstElement *element, GstContext *context);
};

GStreamer element class. Override the vmethods to implement the element functionality.

enum GstElementFlags

typedef enum {
  GST_ELEMENT_FLAG_LOCKED_STATE   = (GST_OBJECT_FLAG_LAST << 0),
  GST_ELEMENT_FLAG_SINK           = (GST_OBJECT_FLAG_LAST << 1),
  GST_ELEMENT_FLAG_SOURCE         = (GST_OBJECT_FLAG_LAST << 2),
  GST_ELEMENT_FLAG_PROVIDE_CLOCK  = (GST_OBJECT_FLAG_LAST << 3),
  GST_ELEMENT_FLAG_REQUIRE_CLOCK  = (GST_OBJECT_FLAG_LAST << 4),
  GST_ELEMENT_FLAG_INDEXABLE      = (GST_OBJECT_FLAG_LAST << 5),
  /* padding */
  GST_ELEMENT_FLAG_LAST           = (GST_OBJECT_FLAG_LAST << 10)
} GstElementFlags;

The standard flags that an element may have.

enum GstState

typedef enum {
  GST_STATE_VOID_PENDING        = 0,
  GST_STATE_NULL                = 1,
  GST_STATE_READY               = 2,
  GST_STATE_PAUSED              = 3,
  GST_STATE_PLAYING             = 4
} GstState;

The possible states an element can be in. States can be changed using gst_element_set_state() and checked using gst_element_get_state().

enum GstStateChange

typedef enum {
  GST_STATE_CHANGE_NULL_TO_READY        = (GST_STATE_NULL<<3) | GST_STATE_READY,
  GST_STATE_CHANGE_READY_TO_PAUSED      = (GST_STATE_READY<<3) | GST_STATE_PAUSED,
  GST_STATE_CHANGE_PAUSED_TO_PLAYING    = (GST_STATE_PAUSED<<3) | GST_STATE_PLAYING,
  GST_STATE_CHANGE_PLAYING_TO_PAUSED    = (GST_STATE_PLAYING<<3) | GST_STATE_PAUSED,
  GST_STATE_CHANGE_PAUSED_TO_READY      = (GST_STATE_PAUSED<<3) | GST_STATE_READY,
  GST_STATE_CHANGE_READY_TO_NULL        = (GST_STATE_READY<<3) | GST_STATE_NULL
} GstStateChange;

These are the different state changes an element goes through. GST_STATE_NULL ⇒ GST_STATE_PLAYING is called an upwards state change and GST_STATE_PLAYING ⇒ GST_STATE_NULL a downwards state change.

enum GstStateChangeReturn

typedef enum {
  GST_STATE_CHANGE_FAILURE             = 0,
  GST_STATE_CHANGE_SUCCESS             = 1,
  GST_STATE_CHANGE_ASYNC               = 2,
  GST_STATE_CHANGE_NO_PREROLL          = 3
} GstStateChangeReturn;

The possible return values from a state change function such as gst_element_set_state(). Only GST_STATE_CHANGE_FAILURE is a real failure.

GST_STATE()

#define GST_STATE(elem)                 (GST_ELEMENT_CAST(elem)->current_state)

This macro returns the current GstState of the element.

GST_STATE_GET_NEXT()

#define GST_STATE_GET_NEXT(cur,pending)         ((GstState)((cur) + __GST_SIGN ((gint)(pending) - (gint)(cur))))

Given a current state cur and a target state pending, calculate the next (intermediate) GstState.

GST_STATE_NEXT()

#define GST_STATE_NEXT(elem)            (GST_ELEMENT_CAST(elem)->next_state)

This macro returns the next GstState of the element.

GST_STATE_PENDING()

#define GST_STATE_PENDING(elem)         (GST_ELEMENT_CAST(elem)->pending_state)

This macro returns the currently pending GstState of the element.

GST_STATE_RETURN()

#define GST_STATE_RETURN(elem)          (GST_ELEMENT_CAST(elem)->last_return)

This macro returns the last GstStateChangeReturn value.

GST_STATE_TARGET()

#define GST_STATE_TARGET(elem)          (GST_ELEMENT_CAST(elem)->target_state)

This macro returns the target GstState of the element.

GST_STATE_TRANSITION()

#define GST_STATE_TRANSITION(cur,next)          ((GstStateChange)(((cur)<<3)|(next)))

Given a current state cur and a next state next, calculate the associated GstStateChange transition.

GST_STATE_TRANSITION_CURRENT()

#define GST_STATE_TRANSITION_CURRENT(trans)     ((GstState)((trans)>>3))

Given a state transition trans, extract the current GstState.

GST_STATE_TRANSITION_NEXT()

#define GST_STATE_TRANSITION_NEXT(trans)        ((GstState)((trans)&0x7))

Given a state transition trans, extract the next GstState.

GST_STATE_GET_LOCK()

#define GST_STATE_GET_LOCK(elem)               (&(GST_ELEMENT_CAST(elem)->state_lock))

Get a reference to the state lock of elem. This lock is used by the core. It is taken while getting or setting the state, during state changes, and while finalizing.

GST_STATE_GET_COND()

#define GST_STATE_GET_COND(elem)               (&GST_ELEMENT_CAST(elem)->state_cond)

Get the conditional used to signal the completion of a state change.

GST_ELEMENT_NAME()

#define GST_ELEMENT_NAME(elem)                  (GST_OBJECT_NAME(elem))

Gets the name of this element. Use only in core as this is not ABI-compatible. Others use gst_element_get_name()

GST_ELEMENT_PARENT()

#define GST_ELEMENT_PARENT(elem)                (GST_ELEMENT_CAST(GST_OBJECT_PARENT(elem)))

Get the parent object of this element.

GST_ELEMENT_BUS()

#define GST_ELEMENT_BUS(elem)                   (GST_ELEMENT_CAST(elem)->bus)

Get the message bus of this element.

GST_ELEMENT_CLOCK()

#define GST_ELEMENT_CLOCK(elem)                 (GST_ELEMENT_CAST(elem)->clock)

Get the clock of this element

GST_ELEMENT_PADS()

#define GST_ELEMENT_PADS(elem)                  (GST_ELEMENT_CAST(elem)->pads)

Get the pads of this elements.

GST_ELEMENT_START_TIME()

#define GST_ELEMENT_START_TIME(elem)            (GST_ELEMENT_CAST(elem)->start_time)

This macro returns the start_time of the elem. The start_time is the running_time of the pipeline when the element went to PAUSED.

GST_ELEMENT_ERROR()

#define             GST_ELEMENT_ERROR(el, domain, code, text, debug)

Utility function that elements can use in case they encountered a fatal data processing error. The pipeline will post an error message and the application will be requested to stop further media processing.

GST_ELEMENT_WARNING()

#define             GST_ELEMENT_WARNING(el, domain, code, text, debug)

Utility function that elements can use in case they encountered a non-fatal data processing problem. The pipeline will post a warning message and the application will be informed.

GST_ELEMENT_INFO()

#define             GST_ELEMENT_INFO(el, domain, code, text, debug)

Utility function that elements can use in case they want to inform the application of something noteworthy that is not an error. The pipeline will post a info message and the application will be informed.

GST_ELEMENT_IS_LOCKED_STATE()

#define GST_ELEMENT_IS_LOCKED_STATE(elem)        (GST_OBJECT_FLAG_IS_SET(elem,GST_ELEMENT_FLAG_LOCKED_STATE))

Check if the element is in the locked state and therefore will ignore state changes from its parent object.

GST_ELEMENT_METADATA_AUTHOR

#define GST_ELEMENT_METADATA_AUTHOR        "author"

Name and contact details of the author(s). Use \n to separate multiple author details. E.g: "Joe Bloggs <joe.blogs at foo.com>"

GST_ELEMENT_METADATA_DESCRIPTION

#define GST_ELEMENT_METADATA_DESCRIPTION   "description"

Sentence describing the purpose of the element. E.g: "Write stream to a file"

GST_ELEMENT_METADATA_DOC_URI

#define GST_ELEMENT_METADATA_DOC_URI       "doc-uri"

Set uri pointing to user documentation. Applications can use this to show help for e.g. effects to users.

GST_ELEMENT_METADATA_ICON_NAME

#define GST_ELEMENT_METADATA_ICON_NAME     "icon-name"

Elements that bridge to certain other products can include an icon of that used product. Application can show the icon in menus/selectors to help identifying specific elements.

GST_ELEMENT_METADATA_KLASS

#define GST_ELEMENT_METADATA_KLASS         "klass"

String describing the type of element, as an unordered list separated with slashes ('/'). See draft-klass.txt of the design docs for more details and common types. E.g: "Sink/File"

GST_ELEMENT_METADATA_LONGNAME

#define GST_ELEMENT_METADATA_LONGNAME      "long-name"

The long English name of the element. E.g. "File Sink"

gst_element_class_add_pad_template ()

void                gst_element_class_add_pad_template  (GstElementClass *klass,
                                                         GstPadTemplate *templ);

Adds a padtemplate to an element class. This is mainly used in the _class_init functions of classes. If a pad template with the same name as an already existing one is added the old one is replaced by the new one.

gst_element_class_get_pad_template ()

GstPadTemplate *    gst_element_class_get_pad_template  (GstElementClass *element_class,
                                                         const gchar *name);

Retrieves a padtemplate from element_class with the given name.

gst_element_class_get_pad_template_list ()

GList *             gst_element_class_get_pad_template_list
                                                        (GstElementClass *element_class);

Retrieves a list of the pad templates associated with element_class. The list must not be modified by the calling code.

gst_element_class_set_metadata ()

void                gst_element_class_set_metadata      (GstElementClass *klass,
                                                         const gchar *longname,
                                                         const gchar *classification,
                                                         const gchar *description,
                                                         const gchar *author);

Sets the detailed information for a GstElementClass.

gst_element_class_set_static_metadata ()

void                gst_element_class_set_static_metadata
                                                        (GstElementClass *klass,
                                                         const gchar *longname,
                                                         const gchar *classification,
                                                         const gchar *description,
                                                         const gchar *author);

Sets the detailed information for a GstElementClass.

Same as gst_element_class_set_metadata(), but longname, classification, description, and author must be static strings or inlined strings, as they will not be copied. (GStreamer plugins will be made resident once loaded, so this function can be used even from dynamically loaded plugins.)

gst_element_class_add_metadata ()

void                gst_element_class_add_metadata      (GstElementClass *klass,
                                                         const gchar *key,
                                                         const gchar *value);

Set key with value as metadata in klass.

gst_element_class_add_static_metadata ()

void                gst_element_class_add_static_metadata
                                                        (GstElementClass *klass,
                                                         const gchar *key,
                                                         const gchar *value);

Set key with value as metadata in klass.

Same as gst_element_class_add_metadata(), but value must be a static string or an inlined string, as it will not be copied. (GStreamer plugins will be made resident once loaded, so this function can be used even from dynamically loaded plugins.)

gst_element_add_pad ()

gboolean            gst_element_add_pad                 (GstElement *element,
                                                         GstPad *pad);

Adds a pad (link point) to element. pad's parent will be set to element; see gst_object_set_parent() for refcounting information.

Pads are not automatically activated so elements should perform the needed steps to activate the pad in case this pad is added in the PAUSED or PLAYING state. See gst_pad_set_active() for more information about activating pads.

The pad and the element should be unlocked when calling this function.

This function will emit the "pad-added" signal on the element.

gst_element_create_all_pads ()

void                gst_element_create_all_pads         (GstElement *element);

Creates a pad for each pad template that is always available. This function is only useful during object initialization of subclasses of GstElement.

gst_element_get_compatible_pad ()

GstPad *            gst_element_get_compatible_pad      (GstElement *element,
                                                         GstPad *pad,
                                                         GstCaps *caps);

Looks for an unlinked pad to which the given pad can link. It is not guaranteed that linking the pads will work, though it should work in most cases.

This function will first attempt to find a compatible unlinked ALWAYS pad, and if none can be found, it will request a compatible REQUEST pad by looking at the templates of element.

gst_element_get_compatible_pad_template ()

GstPadTemplate *    gst_element_get_compatible_pad_template
                                                        (GstElement *element,
                                                         GstPadTemplate *compattempl);

Retrieves a pad template from element that is compatible with compattempl. Pads from compatible templates can be linked together.

gst_element_get_request_pad ()

GstPad *            gst_element_get_request_pad         (GstElement *element,
                                                         const gchar *name);

Retrieves a pad from the element by name (e.g. "src_%d"). This version only retrieves request pads. The pad should be released with gst_element_release_request_pad().

This method is slow and will be deprecated in the future. New code should use gst_element_request_pad() with the requested template.

gst_element_get_static_pad ()

GstPad *            gst_element_get_static_pad          (GstElement *element,
                                                         const gchar *name);

Retrieves a pad from element by name. This version only retrieves already-existing (i.e. 'static') pads.

gst_element_request_pad ()

GstPad *            gst_element_request_pad             (GstElement *element,
                                                         GstPadTemplate *templ,
                                                         const gchar *name,
                                                         const GstCaps *caps);

Retrieves a request pad from the element according to the provided template. Pad templates can be looked up using gst_element_factory_get_static_pad_templates().

The pad should be released with gst_element_release_request_pad().

gst_element_no_more_pads ()

void                gst_element_no_more_pads            (GstElement *element);

Use this function to signal that the element does not expect any more pads to show up in the current pipeline. This function should be called whenever pads have been added by the element itself. Elements with GST_PAD_SOMETIMES pad templates use this in combination with autopluggers to figure out that the element is done initializing its pads.

This function emits the "no-more-pads" signal.

MT safe.

gst_element_release_request_pad ()

void                gst_element_release_request_pad     (GstElement *element,
                                                         GstPad *pad);

Makes the element free the previously requested pad as obtained with gst_element_get_request_pad().

This does not unref the pad. If the pad was created by using gst_element_get_request_pad(), gst_element_release_request_pad() needs to be followed by gst_object_unref() to free the pad.

MT safe.

gst_element_remove_pad ()

gboolean            gst_element_remove_pad              (GstElement *element,
                                                         GstPad *pad);

Removes pad from element. pad will be destroyed if it has not been referenced elsewhere using gst_object_unparent().

This function is used by plugin developers and should not be used by applications. Pads that were dynamically requested from elements with gst_element_get_request_pad() should be released with the gst_element_release_request_pad() function instead.

Pads are not automatically deactivated so elements should perform the needed steps to deactivate the pad in case this pad is removed in the PAUSED or PLAYING state. See gst_pad_set_active() for more information about deactivating pads.

The pad and the element should be unlocked when calling this function.

This function will emit the "pad-removed" signal on the element.

gst_element_iterate_pads ()

GstIterator *       gst_element_iterate_pads            (GstElement *element);

Retrieves an iterator of element's pads. The iterator should be freed after usage. Also more specialized iterators exists such as gst_element_iterate_src_pads() or gst_element_iterate_sink_pads().

The order of pads returned by the iterator will be the order in which the pads were added to the element.

gst_element_iterate_sink_pads ()

GstIterator *       gst_element_iterate_sink_pads       (GstElement *element);

Retrieves an iterator of element's sink pads.

The order of pads returned by the iterator will be the order in which the pads were added to the element.

gst_element_iterate_src_pads ()

GstIterator *       gst_element_iterate_src_pads        (GstElement *element);

Retrieves an iterator of element's source pads.

The order of pads returned by the iterator will be the order in which the pads were added to the element.

gst_element_link ()

gboolean            gst_element_link                    (GstElement *src,
                                                         GstElement *dest);

Links src to dest. The link must be from source to destination; the other direction will not be tried. The function looks for existing pads that aren't linked yet. It will request new pads if necessary. Such pads need to be released manually when unlinking. If multiple links are possible, only one is established.

Make sure you have added your elements to a bin or pipeline with gst_bin_add() before trying to link them.

gst_element_unlink ()

void                gst_element_unlink                  (GstElement *src,
                                                         GstElement *dest);

Unlinks all source pads of the source element with all sink pads of the sink element to which they are linked.

If the link has been made using gst_element_link(), it could have created an requestpad, which has to be released using gst_element_release_request_pad().

gst_element_link_many ()

gboolean            gst_element_link_many               (GstElement *element_1,
                                                         GstElement *element_2,
                                                         ...);

Chain together a series of elements. Uses gst_element_link(). Make sure you have added your elements to a bin or pipeline with gst_bin_add() before trying to link them.

gst_element_unlink_many ()

void                gst_element_unlink_many             (GstElement *element_1,
                                                         GstElement *element_2,
                                                         ...);

Unlinks a series of elements. Uses gst_element_unlink().

gst_element_link_pads ()

gboolean            gst_element_link_pads               (GstElement *src,
                                                         const gchar *srcpadname,
                                                         GstElement *dest,
                                                         const gchar *destpadname);

Links the two named pads of the source and destination elements. Side effect is that if one of the pads has no parent, it becomes a child of the parent of the other element. If they have different parents, the link fails.

gst_element_link_pads_full ()

gboolean            gst_element_link_pads_full          (GstElement *src,
                                                         const gchar *srcpadname,
                                                         GstElement *dest,
                                                         const gchar *destpadname,
                                                         GstPadLinkCheck flags);

Links the two named pads of the source and destination elements. Side effect is that if one of the pads has no parent, it becomes a child of the parent of the other element. If they have different parents, the link fails.

Calling gst_element_link_pads_full() with flags == GST_PAD_LINK_CHECK_DEFAULT is the same as calling gst_element_link_pads() and the recommended way of linking pads with safety checks applied.

This is a convenience function for gst_pad_link_full().

gst_element_unlink_pads ()

void                gst_element_unlink_pads             (GstElement *src,
                                                         const gchar *srcpadname,
                                                         GstElement *dest,
                                                         const gchar *destpadname);

Unlinks the two named pads of the source and destination elements.

This is a convenience function for gst_pad_unlink().

gst_element_link_pads_filtered ()

gboolean            gst_element_link_pads_filtered      (GstElement *src,
                                                         const gchar *srcpadname,
                                                         GstElement *dest,
                                                         const gchar *destpadname,
                                                         GstCaps *filter);

Links the two named pads of the source and destination elements. Side effect is that if one of the pads has no parent, it becomes a child of the parent of the other element. If they have different parents, the link fails. If caps is not NULL, makes sure that the caps of the link is a subset of caps.

gst_element_link_filtered ()

gboolean            gst_element_link_filtered           (GstElement *src,
                                                         GstElement *dest,
                                                         GstCaps *filter);

Links src to dest using the given caps as filtercaps. The link must be from source to destination; the other direction will not be tried. The function looks for existing pads that aren't linked yet. It will request new pads if necessary. If multiple links are possible, only one is established.

Make sure you have added your elements to a bin or pipeline with gst_bin_add() before trying to link them.

gst_element_class_get_metadata ()

const gchar *       gst_element_class_get_metadata      (GstElementClass *klass,
                                                         const gchar *key);

Get metadata with key in klass.

gst_element_set_base_time ()

void                gst_element_set_base_time           (GstElement *element,
                                                         GstClockTime time);

Set the base time of an element. See gst_element_get_base_time().

MT safe.

gst_element_get_base_time ()

GstClockTime        gst_element_get_base_time           (GstElement *element);

Returns the base time of the element. The base time is the absolute time of the clock when this element was last put to PLAYING. Subtracting the base time from the clock time gives the running time of the element.

gst_element_set_start_time ()

void                gst_element_set_start_time          (GstElement *element,
                                                         GstClockTime time);

Set the start time of an element. The start time of the element is the running time of the element when it last went to the PAUSED state. In READY or after a flushing seek, it is set to 0.

Toplevel elements like GstPipeline will manage the start_time and base_time on its children. Setting the start_time to GST_CLOCK_TIME_NONE on such a toplevel element will disable the distribution of the base_time to the children and can be useful if the application manages the base_time itself, for example if you want to synchronize capture from multiple pipelines, and you can also ensure that the pipelines have the same clock.

MT safe.

gst_element_get_start_time ()

GstClockTime        gst_element_get_start_time          (GstElement *element);

Returns the start time of the element. The start time is the running time of the clock when this element was last put to PAUSED.

Usually the start_time is managed by a toplevel element such as GstPipeline.

MT safe.

gst_element_set_bus ()

void                gst_element_set_bus                 (GstElement *element,
                                                         GstBus *bus);

Sets the bus of the element. Increases the refcount on the bus. For internal use only, unless you're testing elements.

MT safe.

gst_element_get_bus ()

GstBus *            gst_element_get_bus                 (GstElement *element);

Returns the bus of the element. Note that only a GstPipeline will provide a bus for the application.

gst_element_set_context ()

void                gst_element_set_context             (GstElement *element,
                                                         GstContext *context);

Sets the context of the element. Increases the refcount of the context.

MT safe.

gst_element_get_factory ()

GstElementFactory * gst_element_get_factory             (GstElement *element);

Retrieves the factory that was used to create this element.

gst_element_set_name()

#define                 gst_element_set_name(elem,name) gst_object_set_name(GST_OBJECT_CAST(elem),name)

Sets the name of the element, getting rid of the old name if there was one.

gst_element_get_name()

#define                 gst_element_get_name(elem)      gst_object_get_name(GST_OBJECT_CAST(elem))

Returns a copy of the name of elem. Caller should g_free() the return value after usage. For a nameless element, this returns NULL, which you can safely g_free() as well.

gst_element_set_parent()

#define                 gst_element_set_parent(elem,parent)     gst_object_set_parent(GST_OBJECT_CAST(elem),parent)

Sets the parent of an element.

gst_element_get_parent()

#define                 gst_element_get_parent(elem)    gst_object_get_parent(GST_OBJECT_CAST(elem))

Get the parent of an element.

gst_element_set_clock ()

gboolean            gst_element_set_clock               (GstElement *element,
                                                         GstClock *clock);

Sets the clock for the element. This function increases the refcount on the clock. Any previously set clock on the object is unreffed.

gst_element_get_clock ()

GstClock *          gst_element_get_clock               (GstElement *element);

Gets the currently configured clock of the element. This is the clock as was last set with gst_element_set_clock().

gst_element_provide_clock ()

GstClock *          gst_element_provide_clock           (GstElement *element);

Get the clock provided by the given element.

gst_element_set_state ()

GstStateChangeReturn gst_element_set_state              (GstElement *element,
                                                         GstState state);

Sets the state of the element. This function will try to set the requested state by going through all the intermediary states and calling the class's state change function for each.

This function can return GST_STATE_CHANGE_ASYNC, in which case the element will perform the remainder of the state change asynchronously in another thread. An application can use gst_element_get_state() to wait for the completion of the state change or it can wait for a GST_MESSAGE_ASYNC_DONE or GST_MESSAGE_STATE_CHANGED on the bus.

State changes to GST_STATE_READY or GST_STATE_NULL never return GST_STATE_CHANGE_ASYNC.

gst_element_get_state ()

GstStateChangeReturn gst_element_get_state              (GstElement *element,
                                                         GstState *state,
                                                         GstState *pending,
                                                         GstClockTime timeout);

Gets the state of the element.

For elements that performed an ASYNC state change, as reported by gst_element_set_state(), this function will block up to the specified timeout value for the state change to complete. If the element completes the state change or goes into an error, this function returns immediately with a return value of GST_STATE_CHANGE_SUCCESS or GST_STATE_CHANGE_FAILURE respectively.

For elements that did not return GST_STATE_CHANGE_ASYNC, this function returns the current and pending state immediately.

This function returns GST_STATE_CHANGE_NO_PREROLL if the element successfully changed its state but is not able to provide data yet. This mostly happens for live sources that only produce data in GST_STATE_PLAYING. While the state change return is equivalent to GST_STATE_CHANGE_SUCCESS, it is returned to the application to signal that some sink elements might not be able to complete their state change because an element is not producing data to complete the preroll. When setting the element to playing, the preroll will complete and playback will start.

gst_element_set_locked_state ()

gboolean            gst_element_set_locked_state        (GstElement *element,
                                                         gboolean locked_state);

Locks the state of an element, so state changes of the parent don't affect this element anymore.

MT safe.

gst_element_is_locked_state ()

gboolean            gst_element_is_locked_state         (GstElement *element);

Checks if the state of an element is locked. If the state of an element is locked, state changes of the parent don't affect the element. This way you can leave currently unused elements inside bins. Just lock their state before changing the state from GST_STATE_NULL.

MT safe.

gst_element_abort_state ()

void                gst_element_abort_state             (GstElement *element);

Abort the state change of the element. This function is used by elements that do asynchronous state changes and find out something is wrong.

This function should be called with the STATE_LOCK held.

MT safe.

gst_element_continue_state ()

GstStateChangeReturn gst_element_continue_state         (GstElement *element,
                                                         GstStateChangeReturn ret);

Commit the state change of the element and proceed to the next pending state if any. This function is used by elements that do asynchronous state changes. The core will normally call this method automatically when an element returned GST_STATE_CHANGE_SUCCESS from the state change function.

If after calling this method the element still has not reached the pending state, the next state change is performed.

This method is used internally and should normally not be called by plugins or applications.

gst_element_lost_state ()

void                gst_element_lost_state              (GstElement *element);

Brings the element to the lost state. The current state of the element is copied to the pending state so that any call to gst_element_get_state() will return GST_STATE_CHANGE_ASYNC.

An ASYNC_START message is posted. If the element was PLAYING, it will go to PAUSED. The element will be restored to its PLAYING state by the parent pipeline when it prerolls again.

This is mostly used for elements that lost their preroll buffer in the GST_STATE_PAUSED or GST_STATE_PLAYING state after a flush, they will go to their pending state again when a new preroll buffer is queued. This function can only be called when the element is currently not in error or an async state change.

This function is used internally and should normally not be called from plugins or applications.

gst_element_state_get_name ()

const gchar *       gst_element_state_get_name          (GstState state);

Gets a string representing the given state.

gst_element_state_change_return_get_name ()

const gchar *       gst_element_state_change_return_get_name
                                                        (GstStateChangeReturn state_ret);

Gets a string representing the given state change result.

gst_element_sync_state_with_parent ()

gboolean            gst_element_sync_state_with_parent  (GstElement *element);

Tries to change the state of the element to the same as its parent. If this function returns FALSE, the state of element is undefined.

gst_element_change_state ()

GstStateChangeReturn gst_element_change_state           (GstElement *element,
                                                         GstStateChange transition);

Perform transition on element.

This function must be called with STATE_LOCK held and is mainly used internally.

gst_element_message_full ()

void                gst_element_message_full            (GstElement *element,
                                                         GstMessageType type,
                                                         GQuark domain,
                                                         gint code,
                                                         gchar *text,
                                                         gchar *debug,
                                                         const gchar *file,
                                                         const gchar *function,
                                                         gint line);

Post an error, warning or info message on the bus from inside an element.

type must be of GST_MESSAGE_ERROR, GST_MESSAGE_WARNING or GST_MESSAGE_INFO.

MT safe.

gst_element_post_message ()

gboolean            gst_element_post_message            (GstElement *element,
                                                         GstMessage *message);

Post a message on the element's GstBus. This function takes ownership of the message; if you want to access the message after this call, you should add an additional reference before calling.

gst_element_query ()

gboolean            gst_element_query                   (GstElement *element,
                                                         GstQuery *query);

Performs a query on the given element.

For elements that don't implement a query handler, this function forwards the query to a random srcpad or to the peer of a random linked sinkpad of this element.

Please note that some queries might need a running pipeline to work.

gst_element_query_convert ()

gboolean            gst_element_query_convert           (GstElement *element,
                                                         GstFormat src_format,
                                                         gint64 src_val,
                                                         GstFormat dest_format,
                                                         gint64 *dest_val);

Queries an element to convert src_val in src_format to dest_format.

gst_element_query_position ()

gboolean            gst_element_query_position          (GstElement *element,
                                                         GstFormat format,
                                                         gint64 *cur);

Queries an element (usually top-level pipeline or playbin element) for the stream position in nanoseconds. This will be a value between 0 and the stream duration (if the stream duration is known). This query will usually only work once the pipeline is prerolled (i.e. reached PAUSED or PLAYING state). The application will receive an ASYNC_DONE message on the pipeline bus when that is the case.

If one repeatedly calls this function one can also create a query and reuse it in gst_element_query().

gst_element_query_duration ()

gboolean            gst_element_query_duration          (GstElement *element,
                                                         GstFormat format,
                                                         gint64 *duration);

Queries an element (usually top-level pipeline or playbin element) for the total stream duration in nanoseconds. This query will only work once the pipeline is prerolled (i.e. reached PAUSED or PLAYING state). The application will receive an ASYNC_DONE message on the pipeline bus when that is the case.

If the duration changes for some reason, you will get a DURATION_CHANGED message on the pipeline bus, in which case you should re-query the duration using this function.

gst_element_send_event ()

gboolean            gst_element_send_event              (GstElement *element,
                                                         GstEvent *event);

Sends an event to an element. If the element doesn't implement an event handler, the event will be pushed on a random linked sink pad for upstream events or a random linked source pad for downstream events.

This function takes owership of the provided event so you should gst_event_ref() it if you want to reuse the event after this call.

MT safe.

gst_element_seek_simple ()

gboolean            gst_element_seek_simple             (GstElement *element,
                                                         GstFormat format,
                                                         GstSeekFlags seek_flags,
                                                         gint64 seek_pos);

Simple API to perform a seek on the given element, meaning it just seeks to the given position relative to the start of the stream. For more complex operations like segment seeks (e.g. for looping) or changing the playback rate or seeking relative to the last configured playback segment you should use gst_element_seek().

In a completely prerolled PAUSED or PLAYING pipeline, seeking is always guaranteed to return TRUE on a seekable media type or FALSE when the media type is certainly not seekable (such as a live stream).

Some elements allow for seeking in the READY state, in this case they will store the seek event and execute it when they are put to PAUSED. If the element supports seek in READY, it will always return TRUE when it receives the event in the READY state.

gst_element_seek ()

gboolean            gst_element_seek                    (GstElement *element,
                                                         gdouble rate,
                                                         GstFormat format,
                                                         GstSeekFlags flags,
                                                         GstSeekType start_type,
                                                         gint64 start,
                                                         GstSeekType stop_type,
                                                         gint64 stop);

Sends a seek event to an element. See gst_event_new_seek() for the details of the parameters. The seek event is sent to the element using gst_element_send_event().

MT safe.

The "no-more-pads" signal

void                user_function                      (GstElement *gstelement,
                                                        gpointer    user_data)       : Run Last

This signals that the element will not generate more dynamic pads. Note that this signal will usually be emitted from the context of the streaming thread.

The "pad-added" signal

void                user_function                      (GstElement *gstelement,
                                                        GstPad     *new_pad,
                                                        gpointer    user_data)       : Run Last

a new GstPad has been added to the element. Note that this signal will usually be emitted from the context of the streaming thread. Also keep in mind that if you add new elements to the pipeline in the signal handler you will need to set them to the desired target state with gst_element_set_state() or gst_element_sync_state_with_parent().

The "pad-removed" signal

void                user_function                      (GstElement *gstelement,
                                                        GstPad     *old_pad,
                                                        gpointer    user_data)       : Run Last

a GstPad has been removed from the element