The Harlem Cultural Festival comprised six concerts that took place between June 29 and August 24, 1969, in Marcus Garvey Park (at the time, Mount Morris Park), and attracted a combined in-person audience of 300,000.
What you hear in the concert sequences is the original audio from the Festival. The quality of the filming meant that nothing really needed to be restored.
The opening credits refer to this film as "A Questlove Jawn." As Questlove explains, a "jawn" is Philadelphia slang for any person, place, or thing.
A huge amount of the footage used in the film was found by accident in a basement where it had sat for 50 years.
Questlove managed to get the 40 hours edited down to two hours by first breaking the footage down to 24 hours. After sitting with that cut for several months, he was then able to whittle it down to three and a half hours before finally excising the last hour and a half. This whole process took a total of five months.