dvdemux date stamp tag only emitted on pad add
A dv stream has date stamps per frame, this data is useful to split a dv by section date.
Currently the date is only retrieved on pad addition.
Date stamp retrieval is done by the function gst_dvdemux_create_global_tag_event
and is only called in gst_dvdemux_add_pad
.
I don't know whether tag events should be sent each frame, when the value changes, or whether this data should not use the event system.