Well spotted john tullamarine!
While musing over the Capn Bloggs video and the improbability of shutting down engines on a line flight (the crew are in uniform after all), I realized that I recognized one of the voices.
I can now confirm the who/when/why. The video is mis-titled in that the session took place in 1980 or 1981 and was filmed by Rohan Craddock (his father was then a B727 captain; while Rohan was the Ansett visual media man). The pilots are, on the left the then Flight Capt (KP) and on the right the Asst Flight Capt (KW) – the three gold bars are correct for that period. The flight was specifically for filming purposes and was intended as part of a training film, though at the time this never saw the light of day.