These ads are seen from past few years. The ads that appear before your video depends upon what video you are going to watch. Theses Ads are one of the important source for YouTube’s revenue,they forces the viewers to watch them.
You can see Two Types of Ads on Youtube:
Steps To Skip These Annoying Ads on Youtube:
1.Ad-Block Plus[Highly Recommended]:
This is available for various browsers especially Google Chrome and Mozilla Firefox.
This Extension not only blocks youtube ads but also block ads on all the websites.