It offers a wide variety of user-generated and corporate media videos. Available content includes video clips , TV show clips, music videos , short and documentary films, audio recordings, movie trailers , live streams , and other content such as video blogging , short original videos, and educational videos. Unregistered users can only watch videos on the site, while registered users are permitted to upload an unlimited number of videos and add comments to videos. Videos deemed potentially inappropriate are available only to registered users affirming themselves to be at least 18 years old. YouTube earns advertising revenue from Google AdSense , a program which targets ads according to site content and audience.