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Trevor's View

Movies On The Internet
Will MPEG-4 Do For Movies What MP3 Did For Audio?

By Trevor Marshall

May 29, 2000

The technology for sending movies over the Internet has arrived.

Technically, it is called MPEG-4, but I will call it MP4. It will change the way we think about computers and entertainment. And just as happened in the early days of MP3, it has spawned an underground network of software developers. Sites like (at least it is honest about its intentions) link to dozens of MP4 players and encoders. But I don't want to focus on the piracy issue. I do believe it's a real issue, but not the one I want to explore now. Rather, let's look at HOW this technology works and the impact it will ultimately have on our industry.

Microsoft Is Again The Villain
Last month, we looked at digital video, particularly the plethora of standards that have driven the television industry over the past four decades. Recall that each country has developed its own way of encoding color TV (NTSC, PAL, etc.), and that the video industry has been reluctant to nurture trans-national standards in its desire to control the distribution and marketing of its products. I quoted Nathan Myrhvold, at that time chief technology officer of Microsoft, saying the following to TV executives in 1993:

"In the last 10 years, we have created an entire industry, and in the next 10 we will create another, whether you help us or not."

Nathan's words were prophetic, for it is Microsoft itself that has opened the Pandora's Box to video piracy.

There is some indication that Microsoft had not fully thought through the implications of what it was really doing when it developed its MPEG-4 video codec. Apparently, Microsoft was initially focusing on the use of the MPEG-4 codec at very low data rates, and was surprised to find that at higher data rates, around 1 megabit per second, its encoder was quite capable of producing TV-quality content.

The initial (beta) builds of the codec (builds 2700 and 3688) functioned perfectly well when used with any audio-visual software, but starting at build 3845, Microsoft started to lock MPG4C32.DLL so that it could only be used with Microsoft's ASF encoding tools, and could not be used to produce an AVI file of pirated content. This is akin to shutting the barn door after the horse has bolted.

Even The Name, DivX, Is Pirated
And in the ultimate twist of irony, the developers are calling the most common pirated MP4 technology DivX (much the same name as Circuit City's abandoned effort to produce self-destructing DVDs). Copies of the hacked and beta versions of the Microsoft codecs are scattered over the Web. While I was researching this article, I came across a site in France that had a copy of the hacked Microsoft codec on its Web pages, but since it also had pirated copies of movie trailers, including the rare "out-takes" of A Bug's Life, I suspect that this site will be taken down soon. There is also an informational page on DivX at the UltimateResourceSite.

MPEG-4 is being developed by the Motion Picture Expert Group as a streaming media (Internet) standard that takes the best of the MPEG-1 and MPEG-2 audio and video technologies, and adds object oriented content (somewhat similar to Flash).

You can get details on all these standards from the MPEG home page, but, in a nutshell, MP4 compresses video in much the same way that MP3 compresses audio. MP3 (MPEG-1 Layer 3) compresses audio based on a knowledge of what we can hear and what we can't. It discards all information in the audio datastream that we probably will not be able to hear, and obtains compression ratios over standard PCM (CD audio) of about a 10-to-1 ratio.

MPEG-2, The Current Digital Video Standard
MPEG-2 is the compression standard that was developed for the television industry, and it is the encoding technology used for DVD disks and DV Camcorders. MPEG-2 does not bother to keep full copies of every frame of a video, but only the details of frames that are changing. Further, a great deal of mathematical prediction is used to estimate what data can be thrown away without the eye being able to notice the changes. While DV consists only of "I" frames, each of which can be displayed on its own, DVD also uses "B" and "P" frames, which contain Predictive and Delta information.

DV Camcorders use a data rate of 25 megabits per second. A one-hour program uses 14 gigabytes of storage. Because of their more advanced IBP encoding, the data rate used for DVD disks is lowered to 10-Mbits per second. Transferring DV or DVD data over today's Internet is just not practical, even when using fast connections. The DVD data rate is still about 100 times greater than that of an MP3 data stream.

Ian Xie, the president of Medio Systems, which licenses some of the best OEM DV and MPEG-2 software codecs, said that Medio's MPEG codecs were now capable of achieving good quality at even lower data rates than DVD. He estimated that a 1,500-kilobit MPEG-2 encoder could deliver about 200 lines of vertical resolution, and that a VHS VCR-quality picture could be obtained with data rates around 2,500 Kbits. He also pointed out that creating content in PAL instead of NTSC gave measurably better results when the video is converted to MPEG, and I will discuss this issue in a future column.

Downloading Video From The Internet
Anybody with a cable or DSL modem knows that it is an easy task to download MP3 music files. The download rate is typically faster than the playing rate, and some programs, like Napster (Beta 6), lets files be played while they are downloading.

Streaming video presents a dilemma, however. In order to get any sort of decent (TV-quality) picture, the data rates have to go up much higher than even a cable modem can handle. In the past, the quality of the video has been reduced in order to fit the available bandwidth. But even a 120-Kbit stream can, at most, deliver a 320 x 240 "thumbnail," hardly a pleasant viewing experience.

MP4 takes the alternative approach. The video is presented as an AVI file for download, and it cannot be streamed. Typical file sizes range from 350 to 800 megabytes for each hour of video content. This gives reasonable quality, full-screen video playback using the Windows Media Player at video data rates between 750 and 1,600 Kbits per second. For legacy compatibility reasons, MP4 encoders typically use MP3 for the audio stream, although the MPEG-4 audio standard will probably supplant MP3 audio in this application.

Video On Standard CD-ROMs
If the MP4 data is being burned onto CD ROMs, excellent quality, at full NTSC resolution (720 x 480), can be achieved with about one hour of video content on each CD. This is considerably better resolution than the 352 x 240 video CDs that have been selling so successfully throughout Asia.

To give you some idea of the results that can be obtained when using MP4, I have converted a DV video clip into MP4 at data rates of 750 Kbits and 1,500 Kbits.

You can download these clips without any worries about piracy, because they are sequences I filmed at my daughter's school play. Of course, you will still need to install a DivX (hacked Microsoft) codec so that Windows Media player can play the clips.

You will also need a reasonably good PC to display the MP4 data stream. I found a 400-MHz Celeron with an AGP ATI graphics card and 32 megs of 66-MHz SDRAM memory is probably about the bare minimum for acceptable real-time decoding performance.

There are two files. The first is an 8-Mbyte download, and contains 90 seconds of video compressed with the DivX encoder at a 600-Kbit rate together with an audio channel of 96-Kbit MP3 stereo. The second is a 15-Mbyte download, and has been encoded at a 1,500-Kbit data rate.

Unzip the files to karen1.avi and karen2.avi, and play them with your Windows Media Player. You will notice that a number of chunky video artifacts are visible in the lower data rate (karen1, 600-Kbit) clip. Luckily, just as MP3 audio quality improves in leaps and bounds as you increase the data rate from 96 to 128 to 160 Kbits, so a doubling of the MP4 video data rate to 1,200 Kbits brings a big improvement in the picture quality.

MP4 is here to stay. Based on my initial observations, Microsoft's MPEG-4 software codec seems to give good picture quality at data rates two to five times lower than the MPEG-2 video solutions I have tried. I will keep an eye on the growth of the Internet-video phenomenon, and report on any new developments. Next month, I will look at some of the tools I used to prepare my sample MP4 videos, and examine the status of MPEG players and encoders for Linux.

Trevor Marshall is an engineering management consultant, with interests ranging from RF and Hardware design to Linux internals, Internet infrastructure, MPEG, and Digital Video. He started his career in the '70s, designing the Maplin Electronic Music Synthesizers. When the Microcomputer came along, he got sidetracked into computer software, programming the 2650, 8080, Z80, Z8000, 8048, 8306, 6805, 80x86, and Power PC families. Along the way, he also picked up a little expertise in RF system design, biomedical engineering, and the printing industry. His web site is

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