| Insider's Guide to MPEG-2 Encoders
- Unedited manuscript for an article published in the October '98 Insiders Guide of the print edition of NewMedia Magazine
- This article covers MPEG (Motion Picture Expert Group) video encoders available at the time of publication (June 1998)...
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- Models & Features
- Open a new window with a table listing available products...revised May2001
Product
MPEG-2 video encoders began as large, dedicated boxes that only service bureaus could afford. Since then, improvements in both software and circuit integration have brought encoder costs down to a level where non-real-time MPEG-2 compression in software can cost as little as $250; real-time hardware solutions now start at around $5k. The current market for MPEG-2 encoders accomodates a wide range of products at varying price/performance levels. So which encoder is right for you? Here's what you should know:
Audience
MPEG-2 is the video format of choice for DVD and Digital TV, and is making its way into intranet-based corporate applications like distance learning.
If you're involved in DVD-Video, you need the level of integration found only on the bigger-ticket items from companies like Sonic Solutions, Minerva and Spruce Technologies. These turnkey packages feature serial digital inputs (SDI) like those found on high-end VTRs, deep adjustability of instantaneous bit rate and GOP structure, advanced motion estimation, and tight integration with a DVD authoring environment. Also characteristic are convenience features such as integrated work flow, real-time preview and serial machine control. Support and service for high-end tools usually scale up along with price.
For DVD-ROM, almost anything works but support for elementary streams and AVI input is desirable. Another bonus is batch processing, which eases the burden of crunching the seemingly endless collection of files needed for game titles.
If you want to deliver MPEG-2 over a network, the ability to encode for lower resolutions and frame rates is essential to accomodate your audience's low bandwidths. Low-cost encoders from companies like Wired and Darim Vision will do the job, and require a minimal investment.
Key Buying Criteria
Of course, since the encoder market evolves very quickly, it's important to invest in a product which can and will be easily upgraded by the manufacturer. Your time budget is also critical. Current software and less-evolved hardware encoders both require non-real-time operation to complete their tasks, especially for VBR encoding. What may seem to be the most important single factor, image quality, really depends on the target audience. Usually, only major motion picture studios are willing to adopt an encoder based on its visual prowess. For the majority of sources, most any VBR encoder will suffice as the bit rate can be momentarily raised to handle the toughest scenes.
For those rare cases where the encoder cannot handle the input without producing visible artifacts, prefiltering will usually save the day. Prefiltering, which softens or blurs the image, reduces the pixel by pixel variation and makes it easier to compress. Most encoders can provide the 4:2:0 MP@ML, though only a handful can deliver the studio production interchange standard 4:2:2 P@ML. MP@ML is limited to 15 Mbps, but not all encoders can deliver that rate. For DVD-Video work, the maximum rate of 9.8 Mbps is available from all of the middle- to high-end offerings. Not surprisingly, the least expensive products support the smaller rates (less than 1 Mbps) necessary for their target audience's low bandwidths. For analog sources, built-in control over active video and sync parameters is convenient, as they determine stability, color balance and dynamic range of the finished image. Some vendors can provide preprocessing, usually as an option, which includes analog controls, filtering and noise reduction.
what about resolution support? Resolution support is another feature that requires consideration of your target audience. Small raster sizes, like low bit rates, allows a restricted bandwidth pipe to carry sufficient data for the application. Support for halfsize horizontal resolution (HHR or 352 pixels) allows deployment to laptop Wintel PCs and halfs the bandwidth required to push those streams over a network. For those forward thinking shoppers eyeing high resolution DTV and DVD-2 delivery, the ability to accept and encode material beyond Main Level will lessen future shock.
Many packages provide integrated audio compression and multiplexing capabilities along with the video, saving time and money for those on a budget. For top notch facilities, a separate audio station yields higher fidelity and more control over the critical end-user listening experience. Splitting the audio and visual work flows can also benefit both productivity and final quality.
The Market
How bright is the future of MPEG 2 video? According to market research firm Strategic Analytics, nearly 23 million homes worldwide will be watching MPEG 2-based digital television by the end of 1998. By 2005, that number will reach 262 million. Sales of DTV set-top boxes (MPEG 2 decoders) are expected to reach 11.4 million units by the end of this year, and will reach 53 million units annually by 2005.
Future Trends
Improvements in circuit integration from CCube and IBM, and a better understanding of the implementation of the MPEG-2 standard will benefit both hardware and software encoders, resulting in increased speed with reduced cost and shrinking form factor. Also, as more consumer products support the variety of high-definition DTV formats (see The Lowdown On HDTV, in the June 2 Media Circus), lower-cost encoders will become available that work beyond MP@ML.
Encoding software will become smarter, taking much of the drudge work off of the operator's plate. Advanced segment reencoding as well as rulesbased preprocessing and bit rate control features will find their way into next-generation products.
Finally, as the industry gains more experience with this segment, expect to see standards develop for the exchange of metadata documenting critical production decisions. This audit trail will improve compression efficiency as video streams will know what specific compression criteria to use for a given scene, instead of forcing the encoder to analyze the segment first.
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by Oliver Masciarotte
- Bio - Oliver Masciarotte is the head honcho at Seneschal where he helps folks become more productive through consulting and training services.
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