To clarify: This post is not about blocking ads when you’re watching YouTube videos. This post is about stopping YouTube from showing ads on your YouTube videos (videos that you yourself uploaded).
It’s not enough to disable monetization of your videos. That will simply not put any money of ads YouTube displays on your videos into your pocket, and put all of it into YouTube’s / Google’s pocket.
What you need to do is go into the Advanced Settings of your YouTube channel.
Then look for “Advertisements” and make sure that “Allow advertisements to be displayed alongside my videos” is disabled (the box next to it needs to be un-checked).
Finally, scroll down and hit the “Save” button.
YouTube will now stop displaying ads in your videos. (Although this doesn’t happen immediately, so don’t be surprised if you still see ads immediately upon making this change).
For a more in-depth tutorial visit http://orgspring.com/turn-off-ads-youtube-videos/