When publishing an individual video, you may want to include a trailer to encourage potential customers to subscribe or purchase the video. The trailer video needs to be uploaded as a video to add it to another video so both the video and the trailer are already uploaded.
Navigate to the video you want to add a trailer for under Content > Videos and click Edit. Under the Appearance tab click Choose Video in the Trailer Video section.
For videos with trailers, the watch trailer button will appear for all potential customers as well as signed in customers.