It mentions “Inside the block callback nothing is flowing between element1
and element2 and nothing will flow until (element1 src) unblocked.”
In element1 srcpad’s block callback pad_probe_cb(), the probe is removed
(unblocked?) first, an event probe is installed on element2’s source pad,
and then EOS is pushed to element2’s sink pad.
Does removing the block probe is to unblock element1 srcpad? If element1
srcpad is unblocked, data continues to flow from element1 to element2. Will
data be lost before element2’s event_probe_cb() is called, in which element2
is removed and element4 is added?