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Multimedia Content Adaptation in MPEG-21

operations tools network capabilities

Definition: MPEG-21 enables the use of multimedia resources across a wide range of networks and devices, and provides multiple adaptation operations such as transcoding, video summarization, replacement, and synthesis.

Content adaptation aims to make content universally accessible (Universal Multimedia Access) depending on terminal capabilities, network, usage and natural environment characteristics. Different networks and terminals imply different quality of service, bit rate, computing and presentation capabilities. MPEG-7, MPEG-21 and a number of adaptation operations aid the development of mechanisms for providing universal multimedia access. While MPEG-7 concentrates on the description of multimedia content and enables quick and efficient searching, identification, processing and filtering of multimedia material, MPEG-21 enables the use of multimedia resources across a wide range of networks and devices. According to their functionality and use for Digital Item Adaptation, the Digital Item Adaptation tools are clustered into three major categories: (i) Usage Environment Description Tools, Digital Item Resource Adaptation Tools and (iii) Digital Item Declaration Adaptation Tools.

The adaptation space comprises of multiple adaptation operations such as transcoding, video summarization, replacement, and synthesis. Similarly, the resource and utility spaces comprise of multiple adaptation operations; the former with transmission, display capabilities, processor speed, power, and memory and the latter with quality or users’ satisfaction of the video content, e.g. PSNR, subjective scores, comprehension level. Adapting content for universal access requires selection of either a single or a combination of operations from all three spaces in order to have the generated content, both best optimized for the network and the target device’ capabilities and for the user. During adaptation the objective is to find a set of adaptation operations that will maximize the utility of the presentation whilst satisfying various constrains, such as terminal and network limitations, always subject to the user’s diversity of preferences.

Using MPEG-21, a user can specify the relative order of each conversion of an original modality and the numeric weight of each conversion. The weights of conversions may help the selection process to determine when conversion should be made. A set MPEG-21 tools namely Terminal and Network QoS describe the relationship between QoS constraints (e.g. on network bandwidth or a terminal’s computational capabilities), feasible adaptation operations that may satisfy these constraints and associated media resource qualities that result from adaptation. The Adaptation QoS descriptor provides the means to trade-off these parameters with respect to quality so that an adaptation strategy can be formulated and optimal adaptation decisions can be made in constrained environments.

Multimedia Content Adaption [next] [back] Multimedia Conferencing

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