The Susi Air pilot was taken hostage on February 7 after landing in the remote region of Nduga.
In the video, which was sent to RNZ Pacific, Mehrtens was instructed to read a statement saying "no foreign pilots are to work and fly" into Highland Papua until Papua is independent.
He made another demand for West Papua independence from Indonesia later in the statement.
Mehrtens was surrounded by more than a dozen people, some of them armed with weapons.
RNZ Pacific has chosen not to publish the video.