aggregator: Start-time selection FIRST/SET does not work by default
In that mode the start time is set when the first buffer arrives. It would be set as the position of the segment, but only if the position of the segment is -1 or if it is further in the future.
Unfortunately the position of the segment is 0 by default (
gst_segment_init()), so it would not be set at all and 0 would be kept.
With compositor and audiomixer this does not seem to be a problem as those are explicitly setting the position in various places to -1 it seems.