Since GST_AGGREGATOR_FLOW_NEED_DATA == GST_FLOW_CUSTOM_ERROR == -100, in order to print the right debug message, we have to check that condition first before comparing ret with GST_FLOW_OK. Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/7663>
Base classes ------------ GstBaseSink FIXME: not much point making it operate in pull mode as a generic base class I guess...