"The directed camera is a massively complicated piece of software just in and of itself. It looks for damage taken by heroes, spells that are cast, item activations, threat determination that seems to tie into how its AI would play out a scenario, nearness to action, what happens in the next 5 seconds, and probably even where players are currently looking.

You won't find any real details anywhere, though."

                This is answer from Decency from same question like yours. Hope it will help.. :)