This is a part of... Well I guess "African American Vernacular English" in general. Basically the English spoken in the ghetto, hood, or racially segregated areas.
Because so many black Americans grew up in these areas and then became big time rappers, AAVE has become, at least in the music industry, a stylish, trendy symbol of 'effortless' richness and coolness (gangster). So, you can find many examples of people, who would never actually speak like that, doing so to achieve its cultural ties. Again, pretty much entirely a top-down thing, that is, only people who were raised in a community that uses that dialect actually speak it, but many young people who don't speak that way still listen to music that does.

AAVE has various qualities:
>uses ain't

>Double negatives work more like they do in Russian
I don't see nobody.

>Less verb conjugation (as seen in the video)

>drops contracted words (only if they can be contracted)
She is working >>> She's working >>> She workin'.
I have got no money >>> I've got no money >>> I got money.

>the habitual 'be'
"She (is) angry." versus "She be angry."
The first is used to refer to a current state, the second is used to refer to a habitual state (She always be angry)

>When spoken for real, it uses slightly different pronunciations, but people imitating the dialect, such as musicians, will often not adopt the pronunciations (because apparently THAT would just be too much to handle) fully and just adopt the grammar.
An artist might only choose to adopt some of the qualities in order to portray just the right amount of "too cool to care about grammar" attitude.

"Ain't nobody got time for that"