Surely Pink Floyd is the strangest mega-successful group in rock history.

Beginning in the mid-'60s as a R&B-based hard rock band like the Who or Pretty Things, the band - Syd Barrett on guitar and vocals, Roger Waters on bass and vocals, Richard Wright on keyboards, and Nick Mason on drums - mutated quickly into an odd combination of twee pop-British psychedelia ("See Emily Play," "Arnold Layne," "The Gnome," "Bike") and long-form instrumental space rock ("Astonomy Domine," "Interstellar Overdrive," "Set the Controls For the Heart of the Sun," "A Saucerful of Secrets"), guided by Barrett's beguiling lysergic explorations - a Cambridge English garden transported to Mars.

But even Ken Kesey, Timothy Leary and Jerry Garcia will tell you (well, they would if they were alive) daily dosing isn't conducive to functioning in the real world and by 1967 Barrett had officially freaked out on acid.

Guitarist David Gilmour, also from Cambridge, joined the group as insurance against Barrett's volatility in '68, but when Barrett was forced from the group for unreliability, the band's management - in one of the most monumental selections of the wrong horse in music history - dumped Floyd in favor of Barrett solo, and what might have been the end was instead a new beginning for the resilient combo (named after Piedmont blues figures Pink Anderson and Floyd Council). What had been largely Syd's backup band became a democratic foursome sharing writing, singing and leadership duties.

The band headed more deeply into experimental symphonic explorations into the depersonalized sonic chill of space, about as far removed from rock 'n' roll's origins in amped-up American teenage hormones as possible; and implausibly, the farther out they went, the more popular they became.

Which brings us to Live At Pompeii, The Director's Cut, a bizarre amalgam of 1971 concert performance shot in the eerily empty ancient Roman amphitheater at Pompeii, interview footage with the band and director Adrien Maben while the film was being assembled in Paris, footage of the band recording the epochal Dark Side of the Moon in '72, all interspliced with trippy 2001-type space shots, computer generated graphics, and freaky volcanic nature footage from nearby Mt. Vesuvius.