MPEG - 4: Cable's new hope for streaming media?

Mon, 07/31/2000 - 8:00pm
Dana Mendell, Executive Editor

As the consumer's hunger for ever more bandwidth and new applications such as broadband multimedia over the Internet grows, cable operators are compelled to keep up with demand by finding more bandwidth-efficient solutions and even more creative ways to deliver content. One technology that's currently piquing the interest of cable operators and manufacturers alike is the MPEG-4 standard, often referred to as the standard for multimedia on the Web (see sidebar, below). What's particularly intriguing about MPEG-4 is that it could offer previously unknown levels of creativity and interactivity for both authors of content and the users of that content. But perhaps of more immediate interest to the cable industry is MPEG-4's ability to function as a standard for streaming media, in the midst of a number of proprietary formats, as well as its ability to handle low-bit-rate applications.

One manifestation of that wellspring of interest is the industry confab that CableLabs held at the end of June, bringing together companies and laboratories conducting research in MPEG-4 technology, including the likes of Philips' Research Lab, Motorola, Microsoft, and Cisco Systems, with interested member companies such as AT&T, Charter, Comcast, Cox, MediaOne, Rogers and Time Warner, for a discussion on the status of the technology.

Richard Green

CableLabs is trying to gather enough data so that the industry can decide if it's wise to go down the MPEG-4 path. "If we're going to use MPEG-4 in the cable industry, and we haven't made that decision yet, but if we were, what would be our profile, what tools would we select," elaborates CableLabs President and CEO Richard Green.

The research organization is taking a close look at MPEG-4 because of the bandwidth savings it could potentially offer the cable industry. "The main reason we are interested in it, is that it provides a step more in terms of bitrate reduction," says Green.

Ultimate in manipulation

Some industry manufacturers see MPEG-4 offering a range of possibilities, from stunning ways to manipulate content, to the benefits of being a true standard.

"In Philips' view, MPEG-4 is a standard multimedia delivery format that's designed for Internet or IP delivery," explains Ahmad Ouri, vice president and general manager of MP4Net at Philips. Ouri also points to the standard's ability to do object-based encoding as an advantage that opens a world of possibilities, including new freedom in content creation and interactivity.

"For content creation with MPEG-4 using object-based coding, you can have several pre-encoded objects in distinct streams that combine together to assemble the desired image at the client side. So instead of creating content in the conventional way (using a lot of sophisticated equipment), you could code an announcer by himself or herself as one object; you could code graphics as separate objects; you could code two different languages of audio as two different objects; and then you can create a scene by assembling all of these different objects and treating them as separate streams. The final stream is assembled based on the production decisions that have been made, and also based on viewer preference," says Ouri.

Figure 1 explains the way in which an audiovisual scene in MPEG-4 is described as composed of individual objects. The figure contains compound media objects that group primitive media objects together. Primitive media objects correspond to leaves in the descriptive tree, while compound media objects encompass entire sub-trees. As an example: The visual object corresponding to the talking person and the corresponding voice are tied together to form a new compound media object, containing both the aural and visual components of that talking person.

Yet another benefit of object-based coding, says Ouri, is the possibilities of interactivity it provides. "If you have separate objects on the screen, you could ideally also attach various URLs or various hyperlinks to different Web sites that are relevant to the displayed objects. If you code a man as one separate object, you could also encode his shirt, or something he is wearing, as a separate object as well, and to that, you can attach a hyperlink. This can be done whether the content is being viewed on a PC or a set-top box. And so, you can enhance the viewer's content viewing experience by enabling e-commerce possibilities," says Ouri.

MPEG-4 could also offer hope for cable operators and set-top manufacturers alike, who are dismayed at the prospect of having to support multiple streaming media software players in advanced digital set-tops. "Because set-tops typically don't have hard disk drives in them, and in relationship to PCs, have a relatively small amount of memory to work with, they have a problem with generalized Web content, where you might see streaming video on the Web that's using RealPlayer at one place, and maybe using one of the other formats somewhere else," says Bill Wall, technical director, subscriber networks, for Scientific-Atlanta.

"Right now, we are in the position that we have to support the decoders for all of those in the set-top. And with the limited software resources, a limited amount of memory within the set-top, it's difficult to do that. Having a single standard in place for streaming content would allow you to be more efficient in the set-top."

Looking a bit farther down the road, S-A's Wall says that MPEG-4's ability to decompose video into separate objects could be a significant advantage.

In the case of video games, "You could be running an MPEG video as background, and have characters in the foreground (graphics characters as part of the game), and you could manipulate them, or others could manipulate them. It allows you to compose scenes, sort of on the fly, with the information that's being transmitted."

Outside of content creation and manipulation, MPEG-4 has the potential to offer other benefits. "Deploying new services like VOD (is) where MPEG-4 becomes a nice conduit," says Ouri. "Number one: It's a standard, and that will prove essential when streaming content to non-PC devices such as set-tops in the short-term, and mobile devices in the future. Number two: It performs very favorably at high bit rates, but also at mid-range bit rates."

If the cable industry does decide to go the MPEG-4 route, one large, looming question is which of the many profiles, or "tools," included in the standard should be embraced by the industry as the most useful.

"There are so many profiles that are defined in MPEG-4, it's going to be difficult for any MPEG-4 decoder to support all of those," says Wall, "so I think the industry is going to have to carefully choose which profiles it really wants to support, which functionality it really wants."

"Right now, it looks like there are about three of those that are important," he adds. "The streaming video profile, the ability to treat video as objects using the object formats, and then the ability to add objects into the video. There are a lot of other things that have gone on in MPEG-4 that may at some point be useful, but probably are not as important today."

One thing is clear: given the rapid pace of technological obsolescence, the goal of achieving better quality and advanced functionality will continue to be a moving target, as the next big thing appears on the horizon tomorrow.

'All my MPEGs . . .'

Established in 1988, the Moving Picture Experts Group (MPEG) is a working group of the International Standards Organization (ISO)/International Electro-technical Commission (IEC). MPEG is a committee within ISO/IEC that's open to experts who are "duly accredited by an appropriate National Standards Body," according to the group's home page ( ).

While MPEG-4 is one of the latest standards birthed by the group, MPEG-1 is the standard on which products such as Video CD and MP3 are based. MPEG-2, essentially developed for the compression and transmission of digital TV signals, is the standard on which products like digital TV set-tops and DVD are based. And what of MPEG-3? Targeted at HDTV (high definition television), it was folded into the MPEG-2 standard.

MPEG-4, formally referred to as the "Coding of Audiovisual Objects," is the standard for multimedia on the Web. In 1993, MPEG-4 started out as "Very Low Bitrate Audiovisual Coding.

"While MPEG-1 and MPEG-2 deal with frame-based video and audio, the MPEG-4 standard describes digital AV scenes as "AV objects" that have certain relations in space and time. Because it's based on objects, MPEG-4 is a powerful standard that offers a new kind of interactivity (with each AV object, and at the levels of coding, decoding or object composition). It also allows for the integration of objects of different natures (e.g. natural video, graphics and text), according to the group.

The group says that targeted applications for the standard include: Internet multimedia, interactive video games, interpersonal communications (videoconferencing, videophone); interactive storage media (optical disks); multimedia mailing; networked database services (via ATM, etc.); remote emergency systems; remote video surveillance; wireless multimedia; and broadcasting.

In terms of specific functionality, MPEG-4 provides a standardized way to describe a scene. For example, it allows the technology user "to place media objects anywhere in a given coordinate system; apply transforms to change the geometrical or acoustical appearance of a media object; group primitive media objects in order to form compound media objects; apply streamed data to media objects, in order to modify their attributes (e.g. a sound, a moving texture belonging to an object; animation parameters driving a synthetic face); and change, interactively, the user's viewing and listening points anywhere in the scene," according to "Overview of the MPEG-4 Standard/Executive Overview," edited by Rob Koenen. (See figure 1, or original chart in Web overview.)

Of course, MPEG-4 is not the MPEG to end all MPEGs. Work on MPEG-21, "Multimedia Framework," began this past June, and current efforts are focused on MPEG-7, "Multimedia Content Description Interface."



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