Video on demand are systems which allow users to select and watch/listen to video or audio content such as movies and TV shows when they choose to, rather than having to watch at a specific broadcast time, which was the prevalent approach with over-the-air broadcasting during much of the 20th century. IPTV technology is often used to bring VOD to televisions and personal computers. Television VOD systems can either "stream" content through a set-top box, a computer or other device, allowing viewing in real time, or download it to a device such as a computer, digital video recorder (also called a personal video recorder) or portable media player for viewing at any time.
The majority of cable- and telephone company-based television providers offer both VOD streaming, free content, whereby a user buys or selects a movie or television program and it begins to play on the television set almost instantaneously, or downloading to a digital video recorder (DVR) rented or purchased from the provider, or downloaded onto a PC or to a portable device, for viewing in the future. Internet television, using the Internet, is an increasingly popular form of video on demand. VOD can also be accessed via desktop client applications such as the Apple iTunes online content store. Some video on demand services, such as Netflix, use a subscription model that requires users to pay a monthly fee to access a bundled set of content, which is mainly movies and TV shows. Other services use an advertising-based model, where access is free. Some airlines offer VOD as in-flight entertainment to passengers through individually controlled video screens embedded in seatback so or armrests or offered via portable media players.