Usually all Gouramis (sans Kissing and the Giant Gourami gourami) build a bubble nest prior to breeding and mate in water that is slow moving. The male will build a bubble nest and then entice the female to join him and spawn. It's a rather delicate "dance" and aggression is not that common. In the case of your 2 fish, you'll notice, early on in the video, that the fish being chased is holding his body straight and more of a fending off position than a breeding position. You'll also notice that the aggressor was grabbing a fin to hold onto the other fish which also is not a breeding position. Considering that there are other gouramis present in the tank and possibly female, I would surmise that they are fighting possibly for breeding rights to those females.
Below is a utube video of breeding Pearl Gouramis so you can see what real breeding behavior looks like