This is a little band called Sneak Thievery playing in Washington Square.
The band has many personel configurations but is most always fronted by trumpet player Jason Prover.
They're really, really, really good!!!.
There's lots of live performance in the Square and also on streets and parks all over the city, and below the streets in the subway stations, and even on the trains themselves.
I once saw five guys put on a very entertaining break dance performance (including back handsprings) on the A Train express between 59th Street and 125th.