IIRC, this is footage from the film "Fighting Black Kings" - atleast that's what it's called in the US. It's a "documentary" of the first Kyokushinkai World Championships that took place the mid-1970s (1975? 1977?) Form what I understand the Kyokushin folks gathered some Muay Thai guys to participate, had them wear karate gis, wrapped brown belts on them and put them on the floor. They did the same with some kung fu guys from Hong Kong (except these folks wore their kung fu outfits) - unfortunately, unlike the Muay Thai guys, these kung fu folks did NOT look like they'd trained extensively (if ever) for full-contact fighting and they made a poor showing. The film's agenda, of course, was to prove the effectiveness & superiority of Kyokushinkai Karate. It features several current high-ranking teachers back when most of them were still under the Kyokushin umbrella - Joko Ninomiya, Shigeru Oyama, Tadashi Nakamura, etc.

The movie focuses on three U.S. competitors (or was it four? been a while since I last saw it) training for and fighting in this competition - all but one of whom happen to be African-Americans (thus the title of the movie!) It screams 70s chop-socky action, but is a cool, classic look at the way things were back then.

OSU the Kings were Sensei William Oliver, Willie "Big Willie" Williams, Charles Martin & Frank Clark. It was also called "The Strongest Karate".