1) audio-plugins elements that implement the tempo-iface, will set the
   control-rate according to tempo, other elements set e.g. sampling-rate/10
2) the default control-rate should be -1 (GST_CLOCKTIME_NONE)
3) when going to playing the baseclasses
3.1) check if there is a controller set for the object (self->priv->controller)
3.2) if yes, for audio they check control-rate
4) when playing if self->priv->controller the baseclasses
4.1) call gst_controller_sync_values
4.3) if control-rate!=-1 segment the processing loop