11.3 MPEG-21: multimedia framework

Today multimedia technology is so advanced that access to the vast amount of information and services from almost anywhere at any time, through ubiquitous terminals and networks, is possible. However, no complete picture exists of how different communities can best interact with each other in a complex infrastructure. Examples of these communities are the content providers, financial, communication, computer and consumer electronics sectors and their customers. Developing a common multimedia framework will facilitate cooperation between these sectors and support a more efficient implementation and integration of different models, rules, interests and content formats. This is the task given to the multimedia framework project under the name of MPEG-21. The name is chosen to signify the coincidence of the start of the project with the 21st century.

The chain of multimedia content delivery encompasses content creation, production, delivery and consumption. To support this, the content has to be identified, described, managed and protected. The transport and delivery of content will undoubtedly be over a heterogeneous set of terminals and networks. Reliable delivery of contents, management of personal data, financial transactions and user privacy are some of the issues that the multimedia framework should take into account. In the following sections the seven architectural key elements that the multimedia framework considers instrumental in the realisation of the task are explained.

11.3.1 Digital item declaration

In multimedia communication to facilitate a wide range of actions involving digital items, there is a strong need for a concrete description for defining exactly what constitutes such an item. Clearly, there are many kinds of content, and nearly as many possible ways of describing it. This presents a strong challenge to lay out a powerful and flexible model for a digital item, from which the content can be described more accurately. Such a model is only useful if it yields a format that can be used to represent any digital item defined within the model unambiguously, and communicate it successfully.

Consider a simple web page as a digital item. This web page typically consists of an HTML (hypertext markup language) document with embedded links or dependencies to various image files (e.g. JPEG images) and possibly some layout information (e.g. style sheet). In this simple case, it is a straightforward exercise to inspect the HTML document and deduce that this digital item consists of the HTML document itself plus all the other resources upon which it depends.

Now let us constrain the above example, such that the web page should be viewed with the JavaScript language. The presence of the language logic now raises the question of what constitutes this digital item and how it can be unambiguously determined. The first problem is that addition of the scripting code changes the declaration of the links, since the links can be determined only by running the embedded script on the specific platform. This could still work as a method of deducing the structure of a digital item, assuming that the author intended each translated version of the web page to be a separate and distinct digital item. This assumption creates a second problem, as it is ambiguous whether the author actually intends for each translation of the page to be a standalone digital item, or whether the intention is for the digital item to consist of the page with the language choice left unresolved. If the latter is the case, it makes it impossible to deduce the exact set of resources that this digital item consists of, which leads back to the first problem. In the course of standardisation MPEG-21 aims to come up with a standard way of defining and declaring digital items.

11.3.2 Digital item identification and description

Currently, the majority of content lacks identification and description. Moreover, there is no mechanism to ensure that this identity and description is persistently associated with the content, which hinders any kind of efficient content storage.

However, some identifiers have been successfully implemented and commonly used for several years, but they are defined in a single media type. ISBN, the International Standard Book Number, or URN, Universal Resource Name, are a few examples of how a digital item can be identified. This is just the beginning and in the future we will see more of these.

There are many examples of businesses, which have requirements for the deployment of a unique identification system on a global scale. Proprietary solutions such as labelling and watermarking for insertion, modification and extractions of IDs have emerged in the past. However, no international standard is available today for the deployment of such technologies, and it is the second task of MPEG-21 to identify and describe them.

11.3.3 Content handling and usage

The availability and access of content within networks is exponentially increasing over time. With the goal of MPEG-21 to enable transparent use of this content over a variety of networks and devices, it becomes extremely important that standards should exist to facilitate searching, locating, caching, archiving, routing, distributing and using content. In addition, the content has to be relevant to the customer needs and provide a better return of money for the business.

Thus the goal of the MPEG-21 multimedia framework is to provide interfaces and protocols that enable creation, manipulation, search, access, storage, delivery and use of content, across the content creation and consumption chain. The emphasis should be given to improve an interaction model for users with personalisation and content handling.

11.3.4 Intellectual property and management

MPEG-21 should provide a uniform framework that enables users to express their rights and interests in, and agreements related to, digital items. They should be assured that those rights, interests and agreements will be persistently and reliably managed and protected across a wide range of networks and devices.

11.3.5 Terminal and networks

Accessibility of heterogeneous content is becoming widespread to many network devices. Today we receive a variety of information through set-top boxes for terrestrial/cable/satellite networks, personal digital assistants, mobile phones etc. Additionally, these access devices are used in different locations and environments. This makes it difficult for service providers to ensure that content is available anywhere, anytime and can be used and rendered in a meaningful way.

The goal of MPEG-21 is to enable transparent use of multimedia resources across a wide range of networked devices. This inevitably has an impact on the way network and terminal resources themselves are being dealt with.

Users accessing content should be offered services with a known subjective quality, perhaps at a known or agreed price. They should be shielded from network and terminal installation, management and implementation issues.

From the network point of view, it is desirable that the application serving the user can translate the user requirements into a network quality of service (QOS) contract. This contract, containing a summary of negotiated network parameters, is handled between the user or his agents and the network. It guarantees the delivery of service over the network for a given QOS. However, the actual implementation of network QOS does not fall within the scope of MPEG-21. The intent is to make use of these mechanisms and propose requirements to network QOS functionality extensions to fulfil the overall MPEG-21 QOS demands.

11.3.6 Content representation

Content is the most important element of a multimedia framework. Within the framework, content is coded, identified, described, stored, delivered, protected, transacted, consumed etc.

Although MPEG-21 assumes that content is available in digital form, it should be represented in a form to fulfil some requirements. For example, digital video as a digital item needs to be compressed and converted into a format to be stored more economically. Although there are several standards for efficient compression (representation) of image and video, they have been devised for specific purposes. Throughout the book we have seen that JPEG and JPEG2000 are some of the standards for coding of still images. For video H.261, H.263, H.26L, MPEG-1, MPEG-2 are used for frame-based video and MPEG-4 is for coding of arbitrary shaped objects. But this is not enough for unique and unambiguous representation of digital video items. The same is true for audio.

In fact users are becoming more mobile and have a need to access information on multiple devices in different contexts at different locations. Currently, content providers and authors have to create multiple formats of content and deploy them in a multitude of networks. Also, no satisfactory automated configurable way of delivering and consuming content exists that scales automatically to different network characteristics and device profiles. This is despite the introduction of various scalable coding of video to alleviate some of these problems.

The content representation element of the framework is intended to address the technology needed in order that content is represented in a way adequate for pursuing the general objectives of MPEG-21. In this regard MPEG-21 assumes that content consists of one or a combination of:

content represented by MPEG standards (e.g. MPEG-4 video)
content used by MPEG but not covered by MPEG standards (e.g. plain text, HTML etc.)
content that can be represented by (i) and (ii) but is represented by different standards or proprietary specifications
future standards for other sensory media.

11.3.7 Event reporting

Every interaction is an event and there is a necessity that events should be reported. However, there are a number of difficulties in providing an accurate report about the event. Different observers of the event may have different perspectives, needs and focuses. Currently there exists no standardised means of event reporting.

In a multimedia environment there are many events that need reporting. For example, accurate product cost, consumer cost, channel costs or profitability information. This allows users to understand operational processes and simulate dynamics in order to optimise efficiencies and outputs.

However, every industry reports information about its performance to other users. A number of issues make this difficult for the receiving users to process this information. For example, different reporting formats, different standards from country to country, different currencies, languages etc. make event processing difficult. As the last key architectural element, MPEG-21 intends to standardise event reporting, to eliminate these shortfalls.