Electronic Design

Wireless Rolls Out The Red Carpet For MPEG-4

Both wireless and server groups are giving MPEG-4 a big boost, and perhaps these efforts will quell the catcalls to the effect that it's about time. This source-coding technology, which became an ISO/IEC standard in 1999, seems to have taken a long time to deploy. But just recently, the Wireless Multimedia Forum (WMF) initiated efforts to adopt MPEG-4 for the source coding of media content to be transported over wireless networks. At the moment, implementing the entire specification would be overkill for a mobile device. So presently, adoption is confined to a subset of the entire MPEG-4 standard.

Another group is on the move with regard to MPEG-4. The Internet Streaming Media Alliance, consisting of server manufacturers such as Cisco, Sun, Apple, and Philips, has carved out its objective to define the first phase of MPEG-4's deployment for servers, so that they will be interoperable and able to stream MPEG-4 content over networks.

Skeptics may say wait a moment, does the world really need another standard? The answer is that MPEG-4 is more than just another compression scheme. Whereas MPEG-2 primarily targets high-quality video at 4 to 15 Mbits/s, MPEG-4 has error resilience, scalability, and hybrid coding of synthetic and natural data as its key objectives. (There's no MPEG-3. Originally intended for HDTV at higher bit rates, it was merged with MPEG-2.)

But what's so vital for wireless is that MPEG-4 has a low bit rate and exhibits high error resistance. One of MPEG-4's rather novel error-correcting techniques is called reversible variable length codes (RVLCs). Such codes can be decoded in either the forward or the backward direction. If part of a bit stream can't be decoded in the forward direction, due to errors, data can be partially recovered by decoding in the backward direction.

Also, MPEG-4 supports scalable content. Encoding the content just once, it can be played at different rates so quality is commensurate with the communications environment at hand. That's another reason why it's such a good fit for mobile communications running at 10 kbits/s.

Sizing up MPEG-4, John Lynch, CEO of e-Vue Inc. in Iselin, N.J., says, "Its range is vast, and there's a lot of technology in it." A spinoff of Sarnoff Laboratories, e-Vue acquired the company's patents and software and is developing them into image and video encoder and player products. Now that massive deployments of this technology are being planned, the challenge is for e-Vue and others to introduce quality technology components, encoders, and decoders that, in turn, will assist in successful and timely product introductions.

The array of Motion Pictures Experts Group (MPEG) standards deals with audio, video—both 2D and 3D—and interactivity. They're also all standardized, right down to the CODEC level.

Like its MPEG-1 and MPEG-2 predecessors, MPEG-4 specifies only the decoding process. Therefore, encoding processes and any improvements are left to the marketplace.

Quality and security are essential to the successful implementation of MPEG-4. With respect to security, digital rights management (DRM) identifies some crucial issues. These encompass policies, encryption, key management, and watermarking. According to these policies, users can view content without saving it. Or, they can view the content for a limited number of times or for a certain period of time.

For more information, go to the MPEG Web site at www.cselt.stet.it/mpeg/. Or read Video Compression, Demystified by Peter Symes, McGraw-Hill, 2001, or Handbook of Image and Video Processing, edited by Al Bovik, Academic Press, 2000, Section VI, Video Processing.

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