Ads during your video If your video is longer than 8 minutes, you can have ads play in the middle of your video. You can choose to have ads placed automatically for you: Watch the video in the mid-rolls editor and check the placement of ads – do they work with the flow of your video? If placing ads manually: Watch your video before and note down at what time there are scene changes …
https://support.google.com/youtube/answer/12929256?hl=en&co=YOUTUBE._YTVideoType%3Dvideo

