Blackmore responds by saying the girl's parents lied to him, telling him she was 16.
The footage presented by the prosecution shows Blackmore expressing fears about incriminating himself because his lawyer isn't present, but he does not deny practicing polygamy.
Many people would be jealous of a family like his, Blackmore tells the officer.
"I am who I am. I've never denied that," he is heard saying in the video.
The polygamy trial began a week ago, hearing from an expert on the history of the Mormon church, who explained how the Utah-based Fundamentalist Church of Jesus Christ of Latter-Day Saints broke away from mainstream Mormonism at the turn of the 20th century.
The Salt Lake City-based Church of Jesus Christ of Latter-day Saints officially abandoned polygamy in 1890 and excommunicates members found practicing it.
Both Blackmore and Oler served as bishops for the Bountiful congregation of the so-called FLDS.
The court also heard last week from a Texas Ranger involved in seizing hundreds of boxes of documents from a ranch owned by the FLDS in 2008.
Dozens of marriage and birth certificates have been entered into evidence at the trial.
The criminal trial has been more than 25 years in the making, with Royal Canadian Mounted Police first investigating allegations that residents of the isolated, religious community were practicing plural or "celestial'' marriage in the early 1990s.
The trial is being heard by a judge alone and is expected to last at least two weeks. Norma Jean Blackmore, who is Blackmore's first wife and Oler's sister, is expected to testify on Tuesday.