I’m not sure what was going on here but it didn’t look friendly (I did move closer and sort of broke it up but the pursuit just carried on into the air).
Most likely a territorial or mating rights dispute. Have a read of Where Song Began for a bit of insight into to the unusual level of aggressiveness in Australian birds. And magpie-larks are some of the worst!
And a couple of photos taken before I took the video (click for larger versions):