In the two hours of unreleased, never-before-seen concert footage that are part of the 40th anniversary DVD edition of Woodstock, the Who come out on stage to perform “My Generation,” which Pete Townshend introduces by saying that it’s “kind of our hymn.” He says, “It’s a song about you and me,” and then, with a sheepish smirk, he adds, “It’s getting’ a bit old now.”

That’s a startling admission to make, given that the song is the rebel yell of someone who would rather die than get old. He’s right, though: The ragged, not-very-angry rendition of “My Generation” that follows sounds like a relic. It doesn’t fit in with the festival’s shiny happy utopian druggie mood, or with the endless, noodling white blues jams that — as these extras make clear — were a far bigger part of Woodstock than the original film indicated. You can see why Michael Wadleigh, the film’s director, decided not to include this performance. “My Generation” is an anthem of defiance, but as the Who thrash it out one more time against the backdrop of a gorgeous sapphire-blue dusk, the images of the blissed-out, placid crowd tell a different story. The audience gathered at Woodstock had already triumphed — over “authority,” and over defiance itself. They didn’t need to fight anymore. They’d won.

To prepare for Woodstock’s big birthday (the festival kicked off 40 years ago this Saturday), I’ve been immersing myself in endless fascinating footage. I’ve seen those newly released concert outtakes (loved Joe Cocker and Johnny Winter; nearly committed hara-kiri during the Grateful Dead’s interminable ramble of “Turn on Your Love Light”). I’ve watched Barbara Kopple’s terrific, lovingly detailed documentary Woodstock: Now & Then, which I could hardly recommend more highly; it will by shown on VH1 this Friday and the History Channel on Monday (it was a co-production of both). I’ve also seen Ang Lee’s light-hearted drama Taking Woodstock, which I’ll review when it comes out in a couple of weeks.

Mostly, though, I went back and saw the original movie, and I marveled, as I always do, at what a singular, pure, earthy, enveloping, anthropologically transporting, altogether miraculous experience it is. It’s the lens, of course, through which just about everyone “remembers” Woodstock, and the lens, if anything, now looms much larger than the original event. Perhaps the most remarkable aspect of Woodstock as a movie is that, although it chronicles a grand and muddy three-day happening that seemed sealed inside an end-of-the-’60s amber of peace-and-love nostalgia from virtually the moment it occurred, the movie doesn’t age. Watch any documentary from the late ’60s through the mid-’70s (like, say, Monterey Pop or Grey Gardens), and it’s almost sure to bear the visual-atmospheric stamps of its time: the shaky vérité camerawork, the distinctive sensual grain of 16mm. But Woodstock has none of that scrappiness. It’s as majestically shot and framed, as air-bubble timeless, as a Stanley Kubrick film.

There’s a reason for that. Michael Wadleigh, now an erudite and charming long-white-haired chap who more or less retired from the movie business after Woodstock, is interviewed at length on one of the DVD extras, and he tells eye-opening stories of how he planned and executed the filming of the festival. Wadleigh and his crew were hired at the last minute, and they had to keep helicoptering in the raw film stock, day after day, if they wanted to keep shooting. It was all very frantic. Yet Wadleigh insisted that special platforms be built into the front of the stage, so that he could get up extremely close to the performers while keeping the cameras relatively stationary. He achieved an on-stage intimacy that’s virtually never been matched.

Then, of course, there are those split-screen images, which may look youth-movie psychedelic but have the paradoxical effect of being the opposite of trippy. What they add up to is a kind of sweepingly “objective,” God’s-eye view — one that immerses us, with a kaleidoscopic perspective worthy of Robert Altman, in the festival’s joy and tumult yet also invites us to contemplate it at a meditative middle distance. Woodstock is the great movie about the ’60s because it takes you totally inside an event that the movie itself, in its promiscuous shifting gaze, remains outside of.

Barbara Kopple gets terrific stories in Woodstock: Now & Then — from Michael Lang, the cagey hippie capitalist who was able to put the festival together because he could talk the language of both generations; from ordinary folks who were there, like a sweet old couple who reveal, touchingly, that they were the pair embracing under a pink blanket on the album’s famous cover shot; and from a variety of musicians who recall what it was like to be up there on that stage. We hear about how Carlos Santana was so high on mescaline during his performance of “Soul Sacrifice” that he thought the neck of his guitar was turning into a snake, and about how Country Joe McDonald had to dash on stage to fill dead air, which is how he ended up performing “I-Feel-Like-I’m-Fixin’-to-Die Rag.” When Jimi Henrdix came on, early on a bedraggled Monday morning, almost the entire massive crowd had already left. He performed “The Star-Spangled Banner” to 40,000 scattered people and piles of trash.

Those blues jams on the extras (Mountain, Canned Heat) are telling. Most of them are done in the indulgent, how long can we play? spirit of Ten Years After’s rendition of “I’m Going Home,” which did make the film’s final cut. (That’s the performance in which Alvin Lee more or less invented “guitar face” — just watch those squints.) But with a few exceptions, notably Hendrix and, of course, Sly & the Family Stone, who seemed so utterly, funkily from-outer-space incongruous at the time (though, in fact, Sly was laying down the groove of the future), the music at Woodstock was very, very white, and looks that way more than ever now. I mean, let’s be honest: It’s not as if the ’60s wasn’t an era of soul music. I would have traded Aretha or Marvin Gaye for three quarters of these acts.

But that’s all part of the genteel yet courageous orgy of boomery middle-classness that was Woodstock. It would be easy, and dismissive, to say that these kids were slumming, but the truth is that camping out for three days with half a million other people was probably no picnic. After all the endless chatter about their generation, they had earned the right to try and go back to the garden. Woodstock was the climax of the ’60s, the mellow orgasm it was seeking, but that’s also why it was the era’s swan song. For a few days, it seemed as if the whole youth culture had melted into one huge mass. But then it was time for everyone to go home, to leave that great big muddy sandbox and become who they really were again.