The video begins by showing Taliban fighters walking on a mountain path. They appear relaxed and comfortable, walking through the area armed but unchallenged. They are heard chatting calmly on their radios.
"Relax, brother," says one.
"Everything is fine in my area," says another.
The night before the attack, they stop to pray. Then, as dawn breaks, the assault begins with a hail of gunfire.
According to an exclusive interview with Taliban commander Maulvi Manibullah, who claims to have organized the operation, the attack involved 150 Taliban fighters dispersed into 30 groups of five. They confronted a few dozen U.S. and Afghan soldiers.
"Residents tipped us off about the base before it opened," Manibullah claimed, "so we took positions in the area. We attacked from four sides."
Gunfire and rocket-propelled grenades set the outpost on fire. U.S. troops are pinned down around their Humvee. In the video, tracers mark their return fire.
But despite withering fire, Taliban fighters move closer, eventually right inside the camp.
"Initially, about 30 fedayeen armed with AK-47s and other weapons forced their entry into the camp and opened fire," Manibullah said. "The foreign soldiers didn't know whether the firing was coming from the inside or from outside the camp."
When the fighting finally ended that day, nine Americans were dead.
Today, say U.S. commanders, the Taliban are showing their strength across the country, from a similar deadly ambush on Camp Keating near the Pakistani border in early October, to the raid on a U.N. compound in downtown Kabul later last month.
Increasingly, the Taliban are establishing a presence even around the capital, Kabul.
Just 30 miles from the city, in Wardak province, Taliban fighters patrol the roads.
"I want all the foreigners to get out of our country," 23-year-old Mawlavi Kiramat, a Taliban fighter, told ABC News.
The Taliban have a ready supply of thousands of recruits -- some fed up with U.S. strikes -- motivated for a holy war against the U.S. military.
"That Kalashnikov [assault rifle] and that label of holy warrior, they are very powerful," said Michael Semple of Harvard University. "They really convey a status that you have little other chance of obtaining."
Back in Nuristan two days after the attack, the outpost was abandoned, along with other small bases. Also in the exclusive video, Taliban fighters are seen making their way inside one of them, examining every inch.
"They have vegetables," said one of them as he walked through the camp. "This is a clinic. And here is where they fired their mortars."
As part of Gen. McChrystal's strategy review, the U.S. is now considering moving away from guarding unpopulated areas, in part because of deadly attacks like the one in Wanat, Nuristan.