Checks if the pad currently has a buffer queued that is going to be used
for the current output frame.
This must only be called from the #GstVideoAggregatorClass::aggregate_frames virtual method,
or from the #GstVideoAggregatorPadClass::prepare_frame virtual method of the aggregator pads.
Checks if the pad currently has a buffer queued that is going to be used for the current output frame.
This must only be called from the #GstVideoAggregatorClass::aggregate_frames virtual method, or from the #GstVideoAggregatorPadClass::prepare_frame virtual method of the aggregator pads.