pre-roll ad
A pre-roll ad is a promotional video message that plays before the content the user has selected. The video advertisements are often repurposed television ads, sometimes shortened to 10 or 15 seconds because the 30-second standard for ads on television is not suitable for videos, which are themselves frequently only a few minutes long.
A new video format known as TrueView allows users to skip the ad after five seconds. However, according to VideoNuze, a video analysis and news website, almost half of all viewers watch pre-roll ads to the end, even if they have the option to skip them.
Pre-roll ads are the most common form of video advertisement. There are also mid-roll and post-roll ads.