Chained compositors causes racy not-negotiated error
This pipeline fails with a not-negotiated error about 75% of the time, but succeeds randomly:
gst-launch-1.0 videotestsrc ! compositor ! video/x-raw,width=1920,height=1080 ! timeoverlay ! compositor name=overlay ! fakesink
Removing either compositor, or the timeoverlay, makes it work reliably. The negotiation error is related to trying to output GstVideoOverlayComposition meta through the capsfilter that disallows it.