The debate over MPEG-4's future is heating up. Its specifications have been available for some time, the MPEG-4 Industry Forum (M4IF) just welcomed its 100th member and the Internet Streaming Media Alliance (ISMA) last month released its open specification for Internet streaming based on MPEG-4. On top of all this, the MPEG-4 community is anxiously awaiting news from patent holders about MPEG-4 licensing, slated to start in January 2002.
MPEG-4 is the first open, comprehensive multimedia content representation standard that will support many multimedia industries, in much the same way that MPEG-2 supports the DVD and television industries. The object-based MPEG-4 standard is both state-of-the art and future-proof; it can easily incorporate improvements in technology if and when they materialize. In fact, a joint ITU-T / MPEG team is adding a new video coding part during the next year, capturing the cutting edge of video-coding technology. In addition, this part will be a standard of the International Telecommunication Union (ITU-T).
Meantime, the Moving Picture Experts Group has not sat still after getting MPEG-4 ready for prime time. Recently, it finalized the first version of the International MPEG-7 Standard for Content Description, to be published by ISO within the next few months. MPEG-7 will complement MPEG-4, not replace it. MPEG-4 defines how to represent content; MPEG-7 specifies how to describe it. And on the horizon there is yet another ISO MPEG standard, MPEG-21, which aims to provide a truly interoperable multimedia framework. The essence of all MPEG efforts is interoperability-interoperability for the consumer. Interoperability means that consumers can use the content and not be bugged by incompatible formats, codecs, metadata and so forth.
MPEG-1 and MPEG-2 provide interoperable ways of representing audiovisual content, commonly used on digital media and on the air. MPEG-4 extends this to many more application areas through features like its extended bit-rate range, its scalability, its error resilience, its seamless integration of different types of 'objects' in the same scene, its interfaces to digital-rights management systems and its powerful ways to build interactivity into content. MPEG-7 defines an interoperable framework for content descriptions way beyond the traditional 'metadata'. MPEG-7 has descriptive elements that range from very 'low-level' signal features like colors, shapes and sound characteristics, to high-level structural information about content collections. MPEG-7 offers unique tools for structuring information about content. MPEG-7 and MPEG-4 form a great couple, especially when MPEG-4 objects are used. With MPEG-7, it is now possible to exchange information about multimedia content in interoperable ways, making it easier to find content and identify just what you wanted to use. MPEG-7 information will be added to broadcasts; personal video recorders and search engines can use it; and it greatly facilitates managing multimedia content in often large content repositories. Audiovisual archives are currently hard to search from outside the organizations that own them, because they all employ their own metadata schemes. MPEG-7 will eliminate that barrier.
All this interoperability sounds promising, but whatever is achieved may be almost completely undone by efforts to protect the digital assets. As digital multimedia spreads to many different platforms, transmission speeds increase and storage costs fall, digital rights management (DRM) becomes necessary to protect the value of content. In its current form, DRM could appear to be working against the very goal of interoperability, as it locks up the 'standardized content' using nonstandardized protection mechanisms. This development is actually not even recent: Many proprietary conditional access (CA) systems make standard MPEG-2 TV content inaccessible to people who happen to own the wrong set-top box-even when they can receive the signal and are willing to pay the associated content fees.
More steps needed
Very early on, MPEG understood that more interoperability in DRM is crucial to the success of an open multimedia infrastructure. While recently a very popular topic in almost every digital forum, five years ago representatives from rights owners, technology providers and CA/DRM providers had already sat down together to discuss the issue in the context of MPEG-4. This gave us the 'hooks': a set of standard interfaces to proprietary Intellectual Property Management and Protection (IPMP) systems, deeply embedded in MPEG-4 Systems. These were a step in the right direction: If you want to play content you 'only' need to plug in the right IPMP system, and where to obtain it can be signaled in the bit stream.
But all this was not enough. A portable music player cannot download an IPMP system-interoperability is lost. (IPMP is MPEG-speak for digital-rights management.) In the summer of 2000 MPEG began work on a more-interoperable IPMP for MPEG-4. This work is now at committee draft stage and will be finalized in May 2002.
Interoperability in digital-rights management is a very hard question. It requires standardized trust. Content owners must, for instance, be able to trust all the players that consume the content. This type of trust is difficult to standardize; the trust infrastructure is not readily available. But, building on its five-year experience with often difficult IPMP discussions, MPEG is perhaps the only forum where the issue can be technically addressed.
This brings us to the MPEG-21 Multimedia Framework. To achieve true end-to-end interoperability takes more than the interoperable IPMP terminal architecture mentioned above. According to its Technical Report (an almost-final version is here), MPEG-21's goal is to describe a "big picture" of how different elements build an infrastructure for the delivery and consumption of related multimedia content-whether existing or under development. In setting the vision and starting the work, MPEG-21 has drawn new blood to MPEG, including representatives from major music labels, the film industry and technology providers.
The MPEG-21 world consists of users that interact with digital items. A digital item can be anything from an elemental piece of content (a single picture, a sound track) to a complete collection of audiovisual works. A user can be anyone who deals with a digital item, from producers to vendors to end users. Interestingly, all users are equal in MPEG-21, in the sense that they all have their rights and interests in digital items, and they all need to be able to express those. For example, usage information is valuable content in itself; an end user will want control over its utilization.
A driving force behind MPEG-21 is the notion that the digital revolution gives every consumer the chance to play new roles in the multimedia food chain. There are 6 billion potential MPEG-21 users out there: producers, packagers, resellers, distributors and so forth. MPEG-21 seeks to use existing standards where possible, to facilitate their integration and to fill in gaps. It does so together with appropriate other standards. Highly laudable and rather abstract, yes, but MPEG is currently drafting a number of very interesting, concrete and commercially relevant parts of the MPEG-21 standard. Counting the MPEG-21 Technical Report as part number one, the second part of MPEG-21 will be ready in the summer of 2002. This is the digital item declaration, a concise and powerful XML-based schema for declaring digital items.
Arguably more ambitious is MPEG-21's third part: the digital item identification and description. This work solves the problem of uniquely identifying digital content in a global way, and giving a resolution mechanism along with the unique identification. Imagine you found a piece of content-got it from a friend, stumbled across it on the Web, received it on a CD-and you want to "consume" it. The content is protected, but the digital item identification tells you where to go to find information about its rights.
The rights information is coded using the two further MPEG-21 parts, the Rights Expression Language (REL) and the Rights Data Dictionary (RDD). These two parts together allow the expression of rights in an interchangeable form, using a standardized syntax (REL, part 5) and standardized terms (RDD, part 6).
The call for proposals for these parts is out. Proposals are due at the end of November; the standards will be ready early in 2003. Probably the Rights Expression Language will be based on XML, but equally likely is that it will also have a compact, binary representation to be used under bandwidth-constrained, real-time conditions. Between parts 3 and 5, the work on more interoperable IPMP in MPEG-4 was recently added to MPEG-21 as its fourth element, because it applies to MPEG-7, -2 and -1 just as well.
The seventh framework element will be a unified description of environments in which content is being used. This covers networks, terminals and access conditions. The goal is to achieve universal multimedia access, where content can adapt itself seamlessly to dynamic-consumption circumstances.
MPEG-21 is developed using a staggered approach, the various parts following each other in time. Future MPEG-21 work items will likely include content representation (how the media resources are represented beyond the existing MPEG standards); content handling and usage (interfaces for managing content); and event reporting.
MPEG-4 is proving its viability in the market as an open standard for multimedia. The ecosystem is coming to life: Players, servers, hardware and software, testing systems, IP cores and authoring tools are all being readied. It will mean a major step toward more interoperability in multimedia. MPEG-7 will help manage the growing abundance of content, and MPEG-21 will make trusted interaction with content more transparent, creating a level playing field for all participants in the multimedia food chain.