What the Heck is MPEG-4?
by Nels Johnson
MPEG is up to level 4 and the demands for it are high. . .
Just when you thought the various flavors of MPEG were finally sorted out, along comes a new member of the family with a whole truckload of hype and mystery surrounding it: MPEG-4. Part of the hoopla, of course, stems from Apple's QuickTime being selected by the International Standards Organization (ISO) as the official foundation for MPEG-4. Much of the rest is based on high expectations being set by
academics and Web theorists, as opposed to Web media producers working in the trenches.
As you may have noticed while running Adobe Premiere for Windows and scrolling your way to Cinepak or Indeo in the compressor list box, Microsoft already has an MPEG-4 codec available for AVI (soon to be ASF) movies. But wait-isn't MPEG a file format, just like AVI and QuickTime? This column covers the major identity issues surrounding MPEG-4, as well as the far-reaching QuickTime/MPEG-4 connection. For the record, MPEG stands for Moving Picture Experts Group, an ISO-sponsored coalition tasked with developing "international standards for compression, decompression, processing, and coded representation of moving pictures and audio."
The MPEG family tree
First, though, from a multimedia production angle, the current MPEG hall of fame:
MPEG-1: In practical terms, the original standard
for high-quality quarter-screen (and smaller), CD-ROM-based desktop video clips. With DirectShow (a.k.a. ActiveMovie) and QuickTime3, most new Windows machines and Macs can play MPEG-1 clips with good results.
MPEG-2: The current standard for high-quality digital video (generally speaking), both broadcast and DVD-based. Today's Windows machines and Macs need additional hardware to play full-screen MPEG-2 streams with Dolby AC-3 audio.
MPEG-3: An abandoned standard. Originally slated to include HDTV, then folded into MPEG-2.
MPEG-4: A standard for so-called "multimedia applications" targeted for the Internet (covered in detail in this column).
MPEG-7: A "content representation" standard for information searches. Still deep in development.
At times, this can seem like a catalog of the diverse types of Kryptonite (each with its own special powers), depending on which expert or technical marketer you talk to. What's important to understand, especially with MPEG-4, is that MPEG is no longer a quality standard (perceived or otherwise), although all MPEG variants are ultimately just data types that play back with different degrees of success on computer desktops or TV screens.
The MPEG-4/QuickTime connection
According to the MPEG coalition (as of this writing), the MPEG-4 specification still has not been finalized. This makes sense once you consider how ambitious the spec has become.
For example, the technical papers available online talk about multiple video and audio objects (e.g., streams), scalability, and progressive downloading across a whole range of bandwidth conditions (see Figure 1). These documents also state that MPEG-4 combines paradigms and technology from digital television (e.g., MPEG-2), interactive graphics applications, and the World Wide Web (for distribution of and access to content). In fact, in the fall of 1997, roll-out of the MPEG-4 standard was split into two phases-essentially to meet a self-imposed deadline. No wonder there's so much hype and mystery.
And where does QuickTime fit into the equation? Based on the MPEG coalition's documentation, as the underlying file format. Does this mean that all MPEG-4 files are QuickTime movies? Not necessarily. But all QuickTime movies (past, present, and future) are now MPEG-4-ready. According to Mitchell Weinstock, Senior QuickTime Product Manager at Apple, "Developers choosing QuickTime today are assured of MPEG-4 file format compatibility in the future." Is QuickTime 3 up to the task of handling all of the streaming, scaling, and general objectivity published in the existing MPEG-4 spec? Based on performance so far, no problem. Will Apple enjoy royalties from multi-media publishers and other developers whose products are built on MPEG-4?
Good question.
A useful analogy here is the compressor vs. file format issue, well understood by most cross-platform developers (see Figure 2). For instance, while you can successfully
convert from AVI to QuickTime with Premiere or TRMOOV (available from www.downrecs.com/software.asp), the converted file won't play the video track unless the compressor (Cinepak, for instance) is supported by both file formats. Similarly, an MPEG-4 file containing media compressed with an unsupported QuickTime codec will not present that media when played by an application such as the QuickTime MoviePlayer.
Does this mean QuickTime will be assimilated by MPEG-4 over time? Don't bet on it. QuickTime is now one of the glitziest jewels in Apple's software crown, and highly proprietary. By the way, while some politics are always involved, it is simply too cynical to think that QuickTime was chosen over Microsoft's ASF/DirectShow for any other reason than plain old merit.
MPEG-4 production and quality issues
So, can you make an MPEG-4 clip right now? Sure-just make a QuickTime movie. But what about the MPEG-4 compressor available in the Microsoft AVI family of codecs? The short answer seems to be that this codec was pressed into service before QuickTime stole the show, thus making it an orphan (since the codec is apparently not supported by the QuickTime file format). Ironically enough, since DirectShow can play QuickTime movies, it can also play MPEG-4 movies. But don't dwell on such ironies for too long.
As noted above, what really generates confusion are the qua-lity issues raised by the MPEG-4 standard. At the most basic design level, MPEG-4 seeks to marry MPEG-2 digital TV (at 3 to 10 megabits per second) with streaming Web video technology. While this may be fine for T3 connectivity, it's not worth discussing even in an ISDN environment. Yet MPEG-4 officially embraces low-bandwidth multimedia as well, as demonstrated by any 28.8 QuickTime/ Sorenson clip streamed via HTTP.
Of course, outright experimentation is always useful for any working multimedia producer. If you're running Premiere for Windows on Windows 95 or NT with Active-Movie installed, try compressing a clip with Microsoft's MPEG-4 Video High Speed Compressor. Choose a Compression Control setting midway between Smoothness and Crispness, a Data Rate of 33kbps (for 56K modems), 10 frames per second, and key frames every few hundred (at least for starters). Set the audio data rate proportionately low (perhaps using the GSM 6.10 audio codec). See for yourself how the result stacks up against RealVideo and Sorenson clips made with similar constraints.
In the past, at least for multimedia developers, MPEG was synonymous with superior quality. Producers invested thousands of dollars in MPEG-1 capture cards just to lock in that high quality, and the cycle is repeating itself in the current MPEG-2 frenzy with even higher prices for capture and mastering hardware. Is MPEG-4 subverting these quality perceptions? Not really. If you dig deep enough to understand the apparent contradictions and get a clear picture of the complete MPEG-4 spec, you won't be sorry or confused. As usual, plenty of information is available on the Web, with the starting point being drogo.cselt.stet.it.
According to the latest documents (as of this writing), MPEG-4's formal ISO/IEC designation will be ISO/IEC 14496. The final version of the spec is scheduled for release in November '98, and MPEG-4 will be an International Standard in January '99. Maybe by then some good recipes for making MPEG-4 movies with Premiere, AfterEffects, MediaStudio Pro, and MediaCleaner Pro will have surfaced.
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