TrueView in-stream ads can appear on:
- YouTube Mastheads
- the Google Play Store
- Google search results and YouTube watch pages
- YouTube watch pages
or
the Google Play Store
YouTube mastheads
Google search results and YouTube watch pages
YouTube watch pages and mobile video mastheads
Explanation:
TrueView in-stream video ads can appear on YouTube watch pages and on videos on partner sites and apps in the Display Network.
Read more here: https://support.google.com/adwords/answer/2375464?hl=en