Video-on-demand: the home video store?

Are videocassettes doomed to follow the path laid by vinyl and Beta? If the many companies now developing video-on-demand (VOD) systems have a say in the matter, the answer is a resounding yes. But not quite yet. The technology behind video-on-demand systems will need to improve in cost and efficiency - before a normal family can simply turn on the TV at will and choose from a Blockbuster-sized selection of film titles, fast forwarding through the dull parts or pausing to answer the phone. This scenario ought to become a reality eventually, but, in the words of Michael Smith, vp of Video-on-Demand at Concurrent Computers, "Only the cable companies are in a position to make this happen any time soon."

Much of the VOD technology is so new that standards are still evolving. Companies large and small - IBM, SunSystems, Celerity - are developing workable systems, some of which can accommodate more than 1,000 simultaneous digital video data streams and have considerable storage space. Bell Atlantic and British Telecom have conducted extensive (and expensive) video-on-demand trials. Cable giant Time Warner continues to develop a real-time, two-way, digital entertainment set-top unit called the Pegasus Set-Top Terminal.

But in many of its basic forms, video-on-demand is already a part of the daily television landscape. Basic VOD service includes the pay-per-view that runs over cable systems (with help from the standard - and relatively slow - telephone line), as well as the entertainment options on certain airline flights (a feature that is sometimes referred to as quasi-video-on-demand). As such, the future of VOD encompasses more than the mere creation of a home video store; it also involves interactive news reporting, learning facilities and banking.

With video-on-demand, pre-recorded videos are digitally stored in a video server. When a video is ordered, it is transmitted in a coded, compressed format and is then decoded and decompressed by a set-top converter in the home. MPEG is the standard, defining the bit-stream representation for synchronised digital video and audio designed to fit a particular bandwith size. The more recently established MPEG-2 offers higher quality and supports a wider range of picture formats (including the current TV picture size and HDTV). With the capacities of hard disks doubling almost every year at a virtually constant cost, the useful compression ratio for video continues to increase. Transmission bandwith will continue to expand upstream and video-on-demand will eventually become less expensive and more viable in homes.

The differences in video-on-demand systems are rooted primarily in the capabilities and limitations of the technology being used. Pay-per-view is considered to be near video-on-demand (NVOD). By definition, NVOD offers viewers access to audiovisual information but provides services at fixed times defined by the service provider. In contrast, true video-on-demand represents an advance, offering access to audio and video information without delay. Yet VOD is incapable of interactive control such as stopping, rewinding or fast-forwarding. Basic systems like pay-per-view or quasi-VOD only require the local controller (or set-top box) to filter multiple channels.

At its most developed, video-on-demand offers expansive options and is entirely interactive. Distinguished by its amount of content storage and the method of delivering the video to the user, interactive video-on-demand (IVOD) remains the high-growth segment of the worldwide multimedia market. Whereas VOD requires only a bidirectional signal from the user to a centralized controller, home IVOD systems need a video server to store and provide access to programs, a data delivery network to connect the subscriber to the system and a set-top box to act as an interface between the home equipment and the VOD service.

An IVOD set-top box has its work cut out for it. The ordinary cable box is a simple decoder. In an IVOD system, the set-top box must control great quantities of information, not only serving as the medium between the television set and the video subscriber network, but also decompressing video and converting it into a standard transmission format. The remote control must provide VCR functions (rewind, fast-forward, etc.) by sending user commands upstream via the channel. The video server, the network equipment that stores the video program material offered to customers, has many functions, including admission control, data retrieval and stream transmission. A server must be able to hold hundreds of megabytes of digital information and offer simultaneous real-time access to thousands of subscribers on a variety of bandwidths. The server must also assess the relative usage and level of interactivity and convert programs into different media (such as magnetic tape and hard disks). A backbone network is also necessary, to connect servers to national or specialized information.

The complexity of IVOD settop boxes and servers is entirely dependent on the venue. As Concurrent's Smith explains, "Systems differ in the amount of content storage used and the approach used to deliver the video to the user." The uses of a video server such as Concurrent's MediaHawk, which offers scalable, high-performance multiprocessor systems, illustrate the different applications of the IVOD system. Airplanes and hotels, for example, require less content storage, thanks to economic and physical constraints. In-flight movies offer a distribution challenge: the server cannot interfere with the plane's navigation functions or take up too much space, and it must have a degree of "reliability" (i.e., not be susceptible to vibration or turbulence). Both hotel and airplane servers, however, usually require only a modest selection of hit movies, whereas a home system's needs are considerably more expansive.

Smith thinks that IVOD will need more muscle before it can enter into mainstream use, and he also believes that costs will have to come down. A MediaHawk server now offers 100 video streams for roughly $25,000 - a prohibitive cost, especially when compared with that of the pay-per-view systems now used in homes. Though the jury. is still out on the industry front-runner, Time Warner's Pegasus Set-Top terminal, its very existence is evidence of a significant cable commitment. And Smith is confident: "I predict that VCRs will slowly phase out to a minimum level over the next five to seven years."