MPEG-21 Digital Item Adaptation
MPEG-21 Digital Item Adaptation specifies the syntax and
semantics of tools that may be used to assist the adaptation of Digital Items,
i.e., the Digital Item Declaration and resources referenced by the declaration.
The tools could be used to satisfy transmission, storage and consumption
constraints, as well as Quality of Service management by the various Users.
It is important to emphasize that the adaptation engines themselves are
non-normative tools of this part of MPEG-21.
The goal of the Terminals and Networks element described in
ISO/IEC 21000-1 is to achieve interoperable transparent access to (distributed)
advanced multimedia content by shielding Users from network and terminal
installation, management and implementation issues. To achieve this goal, the
adaptation of Digital Items is required. This concept is illustrated in
As shown in this conceptual architecture, a Digital Item is subject to a resource
adaptation engine, as well as a description adaptation engine, which together produce
the adapted Digital Item.
Figure 1 — Illustration of Digital Item Adaptation.
(*** click on figure to enlarge ***)
The Digital Item Adaptation tools in this specification are
clustered into eight major categories as illustrated in
Figure 2 — Overview and organization of Digital Item Adaptation tools.
(*** click on figure to enlarge ***)
- The categories are clustered according to their functionality and use for Digital
Item Adaptation around the Schema Tools and Low-Level Data Types. The schema tools
provide uniform root elements for all DIA descriptions as well as some low-level and
basic datatypes which can be used by several DIA tools independently.
- The first major category is the Usage Environment Description Tools, which include
User characteristics, terminal capabilities, network characteristics and natural
environment characteristics. These tools provide descriptive information about the
various properties of the usage environment, which originate from Users, to accommodate,
for example, the adaptation of Digital Items for transmission, storage and consumption.
- The second category is referred to as BSDLink which provides the facilities to create
a rich variety of adaptation architectures based on tools specified within this part of
MPEG-21, MPEG-21 DID, and MPEG-7 MDS among others.
- Bitstream Syntax Description tools comprise the third major category of Digital Item
Adaptation tools. A BSD describes the syntax — in most cases, the high level structure —
of a binary media resource. Using such a description, a Digital Item resource adaptation
engine can transform the bitstream and the corresponding description using editing-style
operations such as data truncation and simple modifications.
- The fourth category of tools is referred to as Terminal and Network Quality of Service.
The tools specified in this category describe the relationship between QoS constraints
(e.g., on network bandwidth or a terminal’s computational capabilities), feasible adaptation
operations satisfying these constraints and associated media resource qualities that result
from adaptation. This set of tools therefore 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.
- The Universal Constraints Description Tools form the fifth category of tools which enables
the possibility to describe limitation and optimisation constraints on adaptations.
- The sixth category is referred to as Metadata Adaptability. This tool specifies hint
information that can be used to reduce the complexity of adapting the metadata contained in
a Digital Item. On the one hand, they are used for filtering and scaling, and on the other
hand, for integrating XML instances.
- For Session Mobility, the seventh category of tools, the configuration state information
that pertains to the consumption of a Digital Item on one device is transferred to a second
device. This enables the Digital Item to be consumed on the second device in an adapted way.
- Finally, the eighth category of tools is referred to as DIA Configuration Tools, which provides
information required for the configuration of a Digital Item Adaptation Engine.
- ISO/IEC 21000-7:2004, Information technology — Multimedia framework (MPEG-21) — Part 7: Digital Item Adaptation