GStreamer Bad Plugins 1.0 Library Reference Manual: GstAggregator

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

## Functions

GstFlowReturn | gst_aggregator_finish_buffer ()
void | gst_aggregator_set_src_caps ()
gboolean | gst_aggregator_iterate_sinkpads ()

## Types and Values

struct | GstAggregator
struct | GstAggregatorClass

## Object Hierarchy

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

## Description

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. Implementers should at least implement the `aggregate()` vmethod.

- 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.

## Functions

### gst_aggregator_finish_buffer ()

    GstFlowReturn
    gst_aggregator_finish_buffer (GstAggregator *agg,
                                  GstBuffer *buffer);

This method will take care of sending mandatory events before pushing the provided buffer.

#### Parameters

self | The GstAggregator |
buffer | the GstBuffer to push. |

### gst_aggregator_set_src_caps ()

    void
    gst_aggregator_set_src_caps (GstAggregator *agg,
                                 GstCaps *caps);

Sets the caps to be used on the src pad.

#### Parameters

self | The GstAggregator |
caps | The GstCaps to set later on the src pad. |

### gst_aggregator_iterate_sinkpads ()

    gboolean
    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.

#### Parameters

self | The GstAggregator |
func | The function to call. |
user_data | The data to pass to `func` . |

## Types and Values

### struct GstAggregator

    struct GstAggregator;

Collectpads object.

#### Members

### struct GstAggregatorClass

    struct GstAggregatorClass {
      GstElementClass   parent_class;

      GType             sinkpads_type;

      GstFlowReturn     (*flush)          (GstAggregator    *  aggregator);

      GstFlowReturn     (*clip)           (GstAggregator    *  agg,
                                           GstAggregatorPad *  bpad,
                                           GstBuffer        *  buf,
                                           GstBuffer        ** outbuf);

      /* sinkpads virtual methods */
      gboolean          (*sink_event)     (GstAggregator    *  aggregate,
                                           GstAggregatorPad *  bpad,
                                           GstEvent         *  event);

      gboolean          (*sink_query)     (GstAggregator    *  aggregate,
                                           GstAggregatorPad *  bpad,
                                           GstQuery         *  query);

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

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

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

      GstFlowReturn     (*aggregate)      (GstAggregator    *  aggregator);

      gboolean          (*stop)           (GstAggregator    *  aggregator);

      gboolean          (*start)          (GstAggregator    *  aggregator);
    };

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.

#### Members

GstElementClass `parent_class`; |  |
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. Should be linked up first. Called when the element goes from PAUSED to READY. The subclass should free all resources and reset its state. |
`start` () | Optional. Should be linked up first. Called when the element goes from READY to PAUSED. The subclass should get ready to process aggregated buffers. |

## See Also

gstcollectpads for historical reasons.