GstAggregator — Base class for mixers and muxers, manages a set of input pads and aggregates their streams



guint64 latency Read / Write
guint64 start-time Read / Write
GstAggregatorStartTimeSelection start-time-selection Read / Write

Types and Values

Object Hierarchy

    ╰── GInitiallyUnowned
        ╰── GstObject
            ╰── GstElement
                ╰── GstAggregator


#include <gst/base/base.h>


Manages a set of pads with the purpose of aggregating their buffers. Control is given to the subclass when all pads have data.

This class used to live in gst-plugins-bad and was moved to core.


gst_aggregator_finish_buffer ()

gst_aggregator_finish_buffer (GstAggregator *aggregator,
                              GstBuffer *buffer);

This method will push the provided output buffer downstream. If needed, mandatory events such as stream-start, caps, and segment events will be sent before pushing the buffer.



The GstAggregator



the GstBuffer to push.

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gst_aggregator_set_src_caps ()

gst_aggregator_set_src_caps (GstAggregator *self,
                             GstCaps *caps);

Sets the caps to be used on the src pad.



The GstAggregator



The GstCaps to set on the src pad.


gst_aggregator_get_latency ()

gst_aggregator_get_latency (GstAggregator *self);

Retrieves the latency values reported by self in response to the latency query, or GST_CLOCK_TIME_NONE if there is not live source connected and the element will not wait for the clock.

Typically only called by subclasses.



a GstAggregator



The latency or GST_CLOCK_TIME_NONE if the element does not sync

gst_aggregator_get_buffer_pool ()

GstBufferPool *
gst_aggregator_get_buffer_pool (GstAggregator *self);



a GstAggregator



the instance of the GstBufferPool used by trans ; free it after use it.

[transfer full]

gst_aggregator_get_allocator ()

gst_aggregator_get_allocator (GstAggregator *self,
                              GstAllocator **allocator,
                              GstAllocationParams *params);

Lets GstAggregator sub-classes get the memory allocator acquired by the base class and its params .

Unref the allocator after use it.



a GstAggregator



the GstAllocator used.

[out][allow-none][transfer full]


the GstAllocationParams of allocator .

[out][allow-none][transfer full]

Types and Values

struct GstAggregator

struct GstAggregator;

Aggregator base class object structure.


struct GstAggregatorClass

struct GstAggregatorClass {
  GstElementClass   parent_class;

  GstFlowReturn     (*flush)          (GstAggregator    *  aggregator);

  GstBuffer *       (*clip)           (GstAggregator    *  aggregator,
                                       GstAggregatorPad *  aggregator_pad,
                                       GstBuffer        *  buf);

  GstFlowReturn     (*finish_buffer)  (GstAggregator    * aggregator,
                                       GstBuffer        * buffer);

  /* sinkpads virtual methods */
  gboolean          (*sink_event)     (GstAggregator    *  aggregator,
                                       GstAggregatorPad *  aggregator_pad,
                                       GstEvent         *  event);

  gboolean          (*sink_query)     (GstAggregator    *  aggregator,
                                       GstAggregatorPad *  aggregator_pad,
                                       GstQuery         *  query);

  /* srcpad virtual methods */
  gboolean          (*src_event)      (GstAggregator    *  aggregator,
                                       GstEvent         *  event);

  gboolean          (*src_query)      (GstAggregator    *  aggregator,
                                       GstQuery         *  query);

  gboolean          (*src_activate)   (GstAggregator    *  aggregator,
                                       GstPadMode          mode,
                                       gboolean            active);

  GstFlowReturn     (*aggregate)      (GstAggregator    *  aggregator,
                                       gboolean            timeout);

  gboolean          (*stop)           (GstAggregator    *  aggregator);

  gboolean          (*start)          (GstAggregator    *  aggregator);

  GstClockTime      (*get_next_time)  (GstAggregator    *  aggregator);

  GstAggregatorPad * (*create_new_pad) (GstAggregator  * self,
                                        GstPadTemplate * templ,
                                        const gchar    * req_name,
                                        const GstCaps  * caps);
  GstFlowReturn     (*update_src_caps) (GstAggregator *  self,
                                        GstCaps       *  caps,
                                        GstCaps       ** ret);
  GstCaps *         (*fixate_src_caps) (GstAggregator *  self,
                                        GstCaps       *  caps);
  gboolean          (*negotiated_src_caps) (GstAggregator *  self,
                                            GstCaps      *  caps);
  gboolean          (*decide_allocation) (GstAggregator * self,
                                          GstQuery * query);
  gboolean          (*propose_allocation) (GstAggregator * self,
                                           GstAggregatorPad * pad,
                                           GstQuery * decide_query,
                                           GstQuery * query);

The aggregator base class will handle in a thread-safe way all manners of concurrent flushes, seeks, pad additions and removals, leaving to the subclass the responsibility of clipping buffers, and aggregating buffers in the way the implementor sees fit.

It will also take care of event ordering (stream-start, segment, eos).

Basically, a simple implementation will override aggregate , and call _finish_buffer from inside that function.


flush ()

Optional. Called after a successful flushing seek, once all the flush stops have been received. Flush pad-specific data in GstAggregatorPad->flush.


clip ()

Optional. Called when a buffer is received on a sink pad, the task of clipping it and translating it to the current segment falls on the subclass. The function should use the segment of data and the negotiated media type on the pad to perform clipping of input buffer. This function takes ownership of buf and should output a buffer or return NULL in if the buffer should be dropped.


finish_buffer ()

Optional. Called when a subclass calls gst_aggregator_finish_buffer() from their aggregate function to push out a buffer. Subclasses can override this to modify or decorate buffers before they get pushed out. This function takes ownership of the buffer passed. Subclasses that override this method should always chain up to the parent class virtual method.


sink_event ()

Optional. Called when an event is received on a sink pad, the subclass should always chain up.


sink_query ()

Optional. Called when a query is received on a sink pad, the subclass should always chain up.


src_event ()

Optional. Called when an event is received on the src pad, the subclass should always chain up.


src_query ()

Optional. Called when a query is received on the src pad, the subclass should always chain up.


src_activate ()

Optional. Called when the src pad is activated, it will start/stop its pad task right after that call.


aggregate ()

Mandatory. Called when buffers are queued on all sinkpads. Classes should iterate the GstElement->sinkpads and peek or steal buffers from the GstAggregatorPads. If the subclass returns GST_FLOW_EOS, sending of the eos event will be taken care of. Once / if a buffer has been constructed from the aggregated buffers, the subclass should call _finish_buffer.


stop ()

Optional. Called when the element goes from PAUSED to READY. The subclass should free all resources and reset its state.


start ()

Optional. Called when the element goes from READY to PAUSED. The subclass should get ready to process aggregated buffers.


get_next_time ()

Optional. Called when the element needs to know the running time of the next rendered buffer for live pipelines. This causes deadline based aggregation to occur. Defaults to returning GST_CLOCK_TIME_NONE causing the element to wait for buffers on all sink pads before aggregating.


create_new_pad ()


update_src_caps ()

Lets subclasses update the GstCaps representing the src pad caps before usage. The result should end up in ret . Return GST_AGGREGATOR_FLOW_NEED_DATA to indicate that the element needs more information (caps, a buffer, etc) to choose the correct caps. Should return ANY caps if the stream has not caps at all.


fixate_src_caps ()

Optional. Fixate and return the src pad caps provided. The function takes ownership of caps and returns a fixated version of caps . caps is not guaranteed to be writable.


negotiated_src_caps ()

Optional. Notifies subclasses what caps format has been negotiated


decide_allocation ()

Optional. Allows the subclass to influence the allocation choices. Setup the allocation parameters for allocating output buffers. The passed in query contains the result of the downstream allocation query.


propose_allocation ()


Property Details

The “latency” property

  “latency”                  guint64

Additional latency in live mode to allow upstream to take longer to produce buffers for the current position (in nanoseconds).

Flags: Read / Write

Default value: 0

The “start-time” property

  “start-time”               guint64

Start time to use if start-time-selection=set.

Flags: Read / Write

Default value: 18446744073709551615

The “start-time-selection” property

  “start-time-selection”     GstAggregatorStartTimeSelection

Decides which start time is output.

Flags: Read / Write

Default value: Start at 0 running time (default)

See Also

gstcollectpads for historical reasons.