After the second friendly-fire cop death this year, NYPD Commissioner James O’Neill said a lesson “can be learned” — but police sources said Tuesday that lesson amounted to a refresher course.

A training video distributed to cops after the February death of Det. Brian Simonsen — cut down by NYPD bullets while responding to a Queens cell-phone store robbery — rehashed established tactics, sources said.

“It’s all about officer safety,” said one source of the video. “Knowing where your partner is, knowing where other officers are. But you can’t always know.”

A second, long-tenured source agreed that the video didn’t offer any new ideas, but still felt it could help green officers with less field experience.

“It would definitely be very beneficial for young cops,” said the insider.

“The Training Bureau has a comprehensive training program in place for recruits during the 6 months they are at the academy, which includes gun-disarming, weapon retention and ground tactics. In addition, the recruits spend three full weeks at the Firearms and Tactics Section located at Rodman’s Neck, where they learn about the safety and fundamentals of firearms proficiency,” the NYPD said in a statement.

Officer Brian Mulkeen was killed by friendly fire early Sunday while wrestling an ex-con at a Bronx housing project for control of his service weapon.