This image was taken a couple of months ago of a species called the Whirring Treefrog, Litoria revelata, from the mid-north coast, where it's relatively abundant in some areas, though it's not a commonly encountered frog in general.
This photo shows, of course, the hold called 'amplexus' where the male (the little yellow fellow in this case) grasps the female in preparation for oviposition. The poor female then has to drag the male around to the spawning site(s) she chooses. Amplexus is either axillary (the male grasps the female in the armpits) as in this species, or inguinal (around the waist).
Male Litoria, at least in my experience, often seem to take on yellow colouration when they're trying to find mates. A classic example is of course the ground dwelling species L. lesueuri and similar. I wonder if it's some sort of advertisement?
Litoria revelata has a high-pitched whirring call, sort of like a sped-up version of the closely related L. verreauxii. At the site where these two were photographed, they can occur in huge numbers, and it's absolutely ear-splitting when the frogs are really going for it. It also seems as if the other species that occur at the site just give up - and shut up - rather than try to compete over the din.