Content Adaptation in Distributed Multimedia Systems
Berhe, Girma, Brunie, Lionel, Pierson, Jean-Marc, Journal of Digital Information Management
Abstract: New developments in computing and communication technology facilitate mobile data access to multimedia application systems such as healthcare, tourism and emergency. In these applications, users can access information with variety of devices having heterogeneous capabilities. One of the requirements in these applications is to adapt the content to the user's preferences, device capabilities and network conditions. In this paper we present a distributed content adaptation approach for distributed multimedia systems. In this approach content adaptation is performed in several steps and the adaptation tools are implemented by external services, we call them adaptation services. In order to determine the type and sequence of the adaptation services, we develop an adaptation graph based on client profile, network conditions, content profile (meta-data) and available adaptation services. Different quality criteria are used to optimize the adaptation graph.
Categories and Subject Descriptors
H.5 [Information Interfaces and Presentation]: Network communications; H.2 [Multimedia Information Systems]; E.I[Data Structures]
Graphs and networks
Keywords: Distributed multimedia systems, content adaptation
Distributed multimedia systems (DMSs) provide access to different media objects such as text, image, video and audio. By extending DMSs with wireless communication components, many new applications become feasible (Gecsei 1997), for example delivering critical information to people in the move (eg patient information to a doctor or nurse, location information to a tourist etc.). Wireless network environment and mobile devices create many challenges that have not been adequately addressed in traditional distributed multimedia systems (Jayaputera et al. 2003). One of the issues is quality of services (QoS) that depends on network conditions (delay, throughput etc.), user's preferences and device capabilities. With many mobile devices being introduced to the market (such as PDAs, Palmtop, Smart-phones, etc) and many of which are unable to display high-resolution graphics, transferring high-resolution images to those mobile devices is not feasible. Moreover, mobile data access results change of user interest with respect to used device and context (time, place etc.).
These conditions lead to create systems that provide content adaptation facilities. By content adaptation we meant that the software is able to scale the content being delivered to the target devices based on the QoS of the wireless network, devices' capability and user's preferences. The idea is, when the network is not good then there is no need to send big data. Some devices are unable to display high-resolution images due to their internal hardware capabilities such as supported color depth, buffer size, etc., in this case low-resolution image can be sent.
The process of content adaptation also referred as transformation is usually applied to the multimedia content in order to satisfy the device and network constraints and user's preferences. Content adaptation includes but not limited to: format conversion (e.g. XML to WML, JPEG to WBMP), scaling of images as well as video and audio streams, media conversion (e.g. text-to-speech), omission or substitution of document parts (e.g. substitution of an image by a textual representation), document fragmentation, language translation, etc (Lei et Georganas 2001).
Content adaptation has been actively explored by many research groups. In general these works can be categorized into two main approaches: static and dynamic (Chang et al. 2002; Lum et al. 2002). In static adaptation, contents in formats specific for each terminal or class of terminals are created and stored by the content provider. This approach has several advantages in terms of delivery performance, specificity to particular device, and full control of the content by the server; however it lacks consideration of dynamic variations of terminal's hardware or software components. …