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GstAggregator — manages a set of pads with the purpose of aggregating their buffers.


gint64 latency Read / Write
guint64 start-time Read / Write
GstAggregatorStartTimeSelection start-time-selection Read / Write

Types and Values

Object Hierarchy

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


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

  • Base class for mixers and muxers. Subclasses should at least implement the GstAggregatorClass.aggregate() virtual method.

  • When data is queued on all pads, tha aggregate vmethod is called.

  • One can peek at the data on any given GstAggregatorPad with the gst_aggregator_pad_get_buffer() method, and take ownership of it with the gst_aggregator_pad_steal_buffer() method. When a buffer has been taken with steal_buffer(), a new buffer can be queued on that pad.

  • If the subclass wishes to push a buffer downstream in its aggregate implementation, it should do so through the gst_aggregator_finish_buffer() method. This method will take care of sending and ordering mandatory events such as stream start, caps and segment.

  • Same goes for EOS events, which should not be pushed directly by the subclass, it should instead return GST_FLOW_EOS in its aggregate implementation.

  • Note that the aggregator logic regarding gap event handling is to turn these into gap buffers with matching PTS and duration. It will also flag these buffers with GST_BUFFER_FLAG_GAP and GST_BUFFER_FLAG_DROPPABLE to ease their identification and subsequent processing.


gst_aggregator_finish_buffer ()

gst_aggregator_finish_buffer (GstAggregator *self,
                              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.

[transfer full]

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_iterate_sinkpads ()

gst_aggregator_iterate_sinkpads (GstAggregator *self,
                                 GstAggregatorPadForeachFunc func,
                                 gpointer user_data);

Iterate the sinkpads of aggregator to call a function on them.

This method guarantees that func will be called only once for each sink pad.



The GstAggregator



The function to call.

[scope call]


The data to pass to func .


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

Types and Values

struct GstAggregator

struct GstAggregator;

Aggregator base class object structure.


struct GstAggregatorClass

struct GstAggregatorClass {
  GstElementClass   parent_class;

  GType             sinkpads_type;

  GstFlowReturn     (*flush)          (GstAggregator    *  aggregator);

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

  /* 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);

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 basic implementation will override aggregate , and call _finish_buffer from inside that function.


GType sinkpads_type;

Optional. The type of the pads that should be created when GstElement.request_new_pad is called.


flush ()

Optional. Called after a succesful 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.


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 ()


Property Details

The “latency” property

  “latency”                  gint64

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

Flags: Read / Write

Allowed values: >= 0

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.

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