Roadblock by Janis Joplin/Big Brother and the Holding Company.
Cool... but that song wasn't part of the Cheap Thrills album shown in the preview. Monterey Pop is a must-see if you like Janis, another film by D A Pennebaker, who made several truly excellent music documentaries during the 60's.

Did you know that Janis Joplin and "Pig Pen" from the Grateful Dead were a thing for awhile? There are some great recordings of her coming up on stage and joining in during Dead concerts. Found these with a quick search, there are probably more.

Grateful Dead Live at Fillmore West on 1969-06-07 : Free Borrow & Streaming : Internet Archive
Set 1 Dire Wolf, Dupree's Diamond Blues, Mountains Of The Moon,Dark Star-> Saint Stephen-> The Eleven-> Sitting On Top Of The World-> Cold Rain & Snow-> Doin'...
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