An Internet Ad Recession?

It seems odd, in light of the momentum behind Google and Facebook, to even talk about a slowdown/recession in Internet advertising. That is a term I hear quite often from folks deep in the industry. The advertising industry is, without question, shifting more dollars from offline ads to online. However, some trends around ad-blocking, and now Apple adding both auto-play and tracking blocking to Safari, signal trends that will impact some of the more basic Internet advertising techniques and could open the door for others beyond Facebook and Google.