From Live at Robert Wyatt's Meltdown (2001), this is the ending of the first part of Shine On You Crazy Diamond, which began with a Gilmour solo on an acoustic. PS: the next song that he starts playing at the the of the video is Terrapin off Syd Barret's The Madcap Laughs. I stopped it just right there so that you'd now rush off to listen to that. Jaw-dropping.
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