Video on demand (VOD) are systems as well as services which allow users to find, select and then watch or listen to favorite audio or video content.
This content is available to users anytime, i.e. when they choose and they don’t have to adapt and watch at a specific broadcast time.
Users can use personal computers or TV sets to receive video on demand when IPTV technology is used. This is often used scenario. In case of television VOD systems VOD content is streamed directly through a set-top box, PC or other device which allows viewing in real time. VOD content can be also downloaded to a VOD compatible device (e.g. computer).
There are several modes of VOD distributions [2] which are briefly described below.
Transactional video on demand
When customers/consumers pay for each particular piece of video on demand content we talk about a distribution model referred as Transactional video on demand (TVOD) or as well as Pay-Per-View VOD or standard VOD. iTunes and Google Play are examples of TVOD services.
Catch up TV
A lot of TV stations in the world (and this number still grows) offer Catch up TV service which allow users to watch TV shows and series through their VOD service for a couple of days after their original broadcasting.
Subscription video on demand
Subscription VOD (SVOD) services are based on a subscription business model. Users don’t pay per view of particular video content (movies, shows, etc.) but they are charged a monthly fee to access unlimited programs. Amazon Video, Hulu Plus, Netflix and HBO Go are examples of SVOD services.
Near video on demand
TV broadcasters who provide multiple channels can use high bandwidth distribution mechanisms (e.g. satellite or cable television) to offer a special pay-per-view video model referred as near video on demand (NVOD). In this type of VOD service a TV program is broadcasted in multiple copies at short time intervals (typically 10–20 minutes). This concept helps viewers to watch program because they don’t have to accommodate for regular scheduled time of program broadcast.
Advertising video on demand
Advertising (or Ad-based) video on demand (AVOD) is a model that is free for the users. Users don’t pay for the content in return for spending time watching ads. An example of AVOD is YouTube.