"We the defence regard this video footage as having political motivation in nature to disguise the truth of the nature of the event," Kar Savuth, the co-defence lawyer, said.
Prosecutors, however, argued that seeing the film was essential, partly because it confirmed that children were held at the jail as well as men and women.
"It is an absolute must for this trial chamber to have all available evidence,"Robert Petit, the co-prosecutor, told the tribunal, adding that he wanted to call the Vietnamese cameraman and other witnesses related to the video.
More than 14,000 people, including many children, are thought to have passed through the S-21 interrogation centre during the four years the Khmer Rouge were in power.
Only a handful survived – most having been taken for execution at sites that later became known as the 'killing fields'.
Duch, who ran the centre, admits atrocities were carried out, but has said he was only acting on the orders of more senior Khmer Rouge leaders.
The seven-minute, black-and-white film shows horrific scenes inside the abandoned prison, a former high school, including several bloated corpses strapped to iron bed frames where they had apparently been tortured.
It also shows five children who survived the retreat of the Khmer Rouge.
Duch, a former maths teacher who converted to Christianity before his arrest, is the first of five former Khmer Rouge leaders to face the much-delayed joint Cambodian-UN tribunal.
|Duch is the first former Khmer
Rouge leader to face trial [EPA]
He is charged with crimes against humanity, war crimes, torture and premeditated murder, and faces life in jail if convicted. Cambodia does not have the death penalty.
Pol Pot, the Khmer Rouge's leader and so-called 'Brother Number One', died in a jungle hideout in 1998.
An estimated 1.7 million people – about a fifth of Cambodia's then population – died during the Khmer Rouge's rule over Cambodia between 1975 and 1979.
Most were executed or died of starvation and overwork.
During the opening session of Duch's trial, lawyers for both sides presented lists of witnesses whose admissibility is now being considered by the court.
Full hearings with testimony from witnesses are not expected to begin until late March at the earliest.