It showed defendants Dritan and Shain Duka visiting the apartment on May 7, 2007. The prosecution alleged they planned to buy four machine guns and three assault rifles.
The brothers appeared nervous, with Dritan Duka asking Omar to close the blinds.
"Just in case," he is heard explaining. "You never know."
The video shows the brothers handling AK-47s and M-16s, discussing how to get them out of Omar's apartment and fretting about sirens heard in the background.
Seconds later, they were arrested.
The video was the first of perhaps 100 recordings the jury is expected to see during the trial.
Five men - all foreign-born Muslims in their 20s - are charged with attempted murder, conspiracy to kill military personnel and weapons offenses. They could be sentenced to life in prison if they are convicted.
The other defendants are a third brother, Eljvir Duka; and two other men, Serdar Tatar and Mohamad Ibrahim Shnewer.
Defense lawyers maintain that there was no sophisticated plot to attack the base and that the government has made innocent activities seem dangerous.
Earlier Tuesday, Col. Ronald Thaxton, the base commander, was called to the stand by prosecutors to outline basic facts about the 30,000-acre Fort Dix, which is currently used to train troops for deployments to Iraq. He said guards at the base's main gate are armed with 9 mm pistols.
Prosecutors say one of the suspects provided a map of the base, and that another conducted surveillance by driving onto the base.
But under cross-examination, Thaxton said civilians can be on base to golf, play or watch soccer matches, visit a museum or even go to a municipal court to contest traffic tickets.
He also acknowledged that maps of the area are available online, but said those maps are not particularly detailed.