Abstract
The diffusion of network appliances such as cellular phones, personal digital assistants (PDAs), and handheld computers creates a new challenge for multimedia content delivery: how to adapt the media transmission to various device capabilities, network characteristics, and user preferences. Each device is characterized by certain display capabilities and processing power. Moreover, such appliances are connected through different types of networks with diverse bandwidths. Finally, users with different preferences access the same multimedia content. To cope with the challenge of delivering content to such a variety of conditions while maximizing user satisfaction, multimedia content needs to be adapted to the needs of the specific application, to the capabilities of the connected terminal and network, and to the preferences of the user (Mohan, Smith, & Li, 1999a; Van Beek, Smith, Ebrahimi, Suzuki, & Askelof, 2003). This adaptation enabling seamless access to multimedia content anywhere and anytime is known as universal multimedia access (UMA). The UMA framework is depicted in Figure 1. Three main strategies for adaptive multimedia content delivery have been proposed, namely, the info pyramid, scalable coding, and transcoding. These strategies, emerging trends in UMA and standardization activities, are discussed in the following sections.