Google recently changed their policy and every YouTube channel will display video ads from other companies by default.
If your YouTube Channel has enough video plays, you can change the ad settings on your channel.
Note these instructions only block future uploads. See Section B below for how to block ads on single videos.
(A) Block Ads from Future Videos you Upload
1. Click on your Logo - Studio
2. Click on Settings
4. Uncheck the Type of Ads you Want to Stop
This example we've blocked all ads from appearing before, during, after and over the top of the videos on your channel.
(B) Block Ads from Appearing on Videos You've Already Uploaded
In Google Studio: