Why put "sync-message"-ed messages into the async queue of bus?
Is it redundant to put the message that has been processed by the
callback of signal "sync-message" into the async queue of a bus? There
isn't a way to set the value of variable `replay` (inside
`gst_bus_post`) to `GST_BUS_DROP` if the message has already been dealt
with in "sync-message" callback.
What is the purpose of it to let each message be (possibly) processed
twice, once in "sync-message" callback, once in whatever function that
takes the message away from the async queue?