How I can be sure if a youtube link is an ads?

[jfb]

If the content is coming from the same domain as the ads, you will get the ads as well as the video. This is common with YouTube. There is a very long running thread on YouTube videos:

How do I block ads on YouTube?

Update 2020-10-24 It's not likely that you'll be able to block in-video ads with Pi-hole. For that, you'll need something like uBlock origin for desktop, or vanced for android (Now defunct), This thread has been closed as there is not much more discussion to be had around the topic. Update 2018-11-14 User's have had good success here: I'm updating this top-level post as of 2018-10-16 since a lot of people land here. Blocking ads on YouTube is hit or miss with Pi-hole. The reason for th…