NEW YORK -- Questlove responded with incredulous disbelief when he was first told about the footage.

A landmark 1969 Harlem concert series that he hadn't heard of? With Stevie Wonder? With Nina Simone? With Sly and the Family Stone, B.B. King and the Staples Singers?

鈥淚 was like, `Yeah, right.' I know everything that musically happened during that time period and I've never heard of this in my life. `Get out of here,鈥' Ahmir 鈥淨uestlove鈥 Thompson recalled in an interview. 鈥淭hen they came back and showed me the footage and I was just jaw-dropped.鈥

That was the beginning of what would become 鈥淪ummer of Soul (...or When the Revolution Could Not Be Televised),鈥 a concert-film time-capsule of a historic but largely forgotten festival. Known as 鈥淏lack Woodstock,鈥 the festival occurred during the same summer as Woodstock - and just 100 miles away - but received far less attention.

鈥淪ummer of Soul,鈥 Questlove's directorial debut, finally unearths a little-seen landmark musical event. It debuted Thursday night at the Sundance Film Festival where it spawned immediate acclaim and countless at-home dance parties for virtual festivalgoers - a party Questlove extended with a live-streamed after-party DJ set.

As the Roots drummer, the 鈥淭onight鈥 show bandleader, an in-demand producer and a self-declared 鈥渕usic nerd,鈥 Questlove's ubiquitous presence in music has often bled into film projects. But 鈥淪ummer of Soul鈥 is his first time directing - his first 鈥渏awn,鈥 as he labels it, using Philadelphia slang - even if he never sought it out.

鈥淵ou're asking if this was on my bucket-list bingo card?鈥 says Questlove smiling over Zoom.

鈥淚n my head, I was thinking in a more seasoned director's hands, this could change someone's life,鈥 he says. 鈥淚 knew I was watching something special. But I got over my fear. I often will go through impostor syndrome. I realized now it's my chance to change someone's life and tell a story that was almost erased.鈥

Over six Sundays in 1969, more than 300,000 gathered in Harlem's Mt. Morris Park for a celebration of soul, gospel, funk and, most of all of Black identity at a pivotal point in African American culture. The festival - 鈥渓ike a rose coming through the concrete鈥 one attendee remembers - came a year after Martin Luther King Jr.'s assassination. Rev. Jesse Jackson is seen speaking passionately from the stage: 鈥淲hen we're more concerned about the moon than men, somebody better wake up.鈥

The concerts were filmed by the television veteran Hal Tulchin, but he found that no networks or Hollywood producers were interested in his 40 hours of footage. Tulchin kept trying to find the footage a home before his death in 2017.

鈥淟iterally, had we let a few months more go by, a lot of this footage would have been discarded in the trash,鈥 says Questlove. 鈥淗al Tulchin had been trying to sell this footage for years and years and decades and decades. Nobody would take the bait. His wife was like: I know some of his stuff is in the basement but I'm about to clear the basement and get rid of it. Who knew that you could get Stevie Wonder for so cheap, or Sly and the Family Stone?鈥

The material is indeed jaw-dropping. Simone, perhaps for the first time, performs 鈥淭o Be Young, Gifted and Black.鈥 Sly and the Family Stone, the only act to play both Woodstock and Harlem in 1969, plays 鈥淚 Want to Take You Higher.鈥 Hugh Masekela does 鈥淕razing in the Grass.鈥 Mahalia Jackson and Mavis Staples sing an astonishing gospel duet.

鈥淭he more I watched it, especially with the gospel performances, that's just some of the prime, documented, raw gospel performances I've ever seen in my lifetime,鈥 says Questlove. 鈥淚 was just like: Yo, is it that easy just to erase our history? Is it that easy, in a snap? Could it just be lost? That one scene, alone, with Mahalia Jackson and Mavis Staples, that almost was in the trash. That was the number one thing in my mind: How easy is it for history to be erased? And why does this mainly always happen to Black people?鈥

Questlove had set out initially to focus purely on the music. His first cut was 3 hours and 25 minutes. 鈥淎mateur hour,鈥 jokes Questlove, whose final cut runs 117 minutes. But as he worked on the film through Black Lives Matter protests, through the pandemic and through the reckoning that followed the death of George Floyd, the scope of 鈥淪ummer of Soul鈥 kept enlarging.

鈥淭he purpose of this festival was to keep people's minds occupied and give them something to look forward to in the summer of 1969. To see that happening in real-time in 2019, I realized that we had to dig deeper into the role of the artist,鈥 says Questlove. 鈥淎s time went on, I started seeing this movie in a whole other way. Had the events of 2020 not occurred, this film wouldn't be the film that it is now. The parallels were too much to ignore.鈥