MPEG Encoding and Decoding Solutions

Products that take the mystery out of MPEG

Moving Pictures Experts Group (MPEG) is the International Standards Organization’s (ISO’s) committee that developed the MPEG-1 and MPEG-2 video-compression methods. The high-quality resolution and significant compression ratios of the MPEG-2 format make it the chosen video compression method for DVD media and satellite broadcasts. Recording (i.e., encoding) and decoding MPEG-2 streams is the resource-intensive task of dedicated hardware. For this month's concluding review of multimedia technology, I tested Sigma Designs’ REALmagic Hollywood Plus MPEG-2 PCI decoder card and REALmagic NetStream 2 MPEG-2 PCI decoder card. I also reviewed FutureTel’s PrimeView NS Model 325 MPEG-2 encoder card. Before I dive into these reviews, I’ll give you a brief overview of the MPEG format.

The MPEG format. The MPEG committee created the MPEG standard to provide a format for compressed digital video on a standard compact disc, which has a maximum data transfer rate of only 1.416Mbps. The MPEG-1 standard offers a resolution of 352 × 240 pixels at 30 frames per second for the NTSC standard, and 352 × 288 pixels at 25 frames per second for the PAL standard. Several software applications, such as Microsoft’s Media Player, decode MPEG-1 content, and any MPEG-2 device can decode MPEG-1 content, because MPEG-1 is a subset of MPEG-2.

The MPEG committee developed MPEG-2 to satisfy the needs of the broadcast television industry’s cable and satellite networks, which aren’t limited to the data throughput of a compact disc. A single-speed DVD runs about seven or eight times faster than a compact disc; thus, the MPEG committee developed MPEG-2 and eliminated the speed barrier to MPEG content on the DVD medium. The MPEG-2 format offers a resolution of 704 × 480 pixels in 24-bit (i.e., 16.8 million) color at 30 frames per second for the NTSC standard, and 704 × 576 pixels at 25 frames per second for the PAL standard.

MPEG compression works by encoding only the information that changes between successive video frames, rather than encoding all the information in each frame. For example, in a video of a beach scene that shows sand in the foreground, blue sky in the background, and a boat moving across the horizon, the sand and sky don’t change—only the position of the boat with respect to the frame’s edges changes. In each successive frame, MPEG uses a cached background from a previous frame and records only the changed portions of the frame (the boat in this example) to compile a complete image.

An MPEG stream contains two layers. The compression layer includes compressed audio and video streams, and the system layer includes timing and synchronization information for audio and video streams.

Motherboard manufacturers are considering embedding MPEG-2 decoding application-specific integrated circuits (ASICs) in their future products. This development isn’t surprising if you consider the effort involved in decoding an MPEG-2 stream at 30 frames per second. However, MPEG technology is readily available today, as this month’s product reviews show.

REALmagic Hollywood Plus and REALmagic NetStream 2
Sigma Designs’ REALmagic Hollywood Plus offers MPEG-2 decoding for DVD-ROM-based content, and REALmagic NetStream 2 provides MPEG-2 decoding for network content. MPEG-2 decoding is a processor-intensive task, so hardware devices such as these are the norm for decoding MPEG-2 content.

Vendors often bundle their DVD-ROM drives with an MPEG-2 decoding card because DVD-ROM drives alone do little more than read the content of densely packed DVD media. Decoding cards, such as Hollywood Plus, decompress MPEG-2 content and assemble it into streams for viewing in a process called demultiplexing.

Unlike the Hollywood Plus card, the NetStream 2 PCI card doesn’t need a DVD-ROM drive to operate. The NetStream 2 card is a standalone product that works in networked video environments. As far as I know, NetStream 2 is the only card of its kind.

Sigma Designs bundles these cards with Windows 98 drivers. To install either card, you need to go to the Sigma Designs Web site and download the Windows NT drivers. I encountered no difficulties installing the NetStream 2 card on a dual 400MHz Xeon Pentium II Dell Precision WorkStation 610, 500MHz Pentium III IBM IntelliStation, dual 333MHz Pentium II Intergraph TDZ-2000, 300MHz Pentium II Digital PC 3000, and 166MHz Pentium MMX with 64MB of RAM. However, I had trouble loading the Hollywood Plus decoder card drivers in all those systems, in addition to a dual 450MHz Xeon Pentium II Compaq Professional Workstation SP700. The only system the Hollywood Plus card ran in is a 400MHz Celeron Compaq DeskPro EN. My installation troubles led me to the Hardware Compatibility List (HCL) on Sigma Designs’ Web site. Most of the systems I tried to install the card in have high-end graphics cards that the Hollywood Plus card doesn’t support. I also learned that the card doesn’t support dual-processor systems. A Sigma Designs’ representative told me that the company is working on a multiprocessor driver, which it will post on its Web site when available.

To start working with either card, you need to plug the card into a PCI slot and connect a video overlay cable from the card to your graphics adapter. Your monitor plugs into the Sigma Designs cards. Sigma Designs provides both cards with a short audio cable you can use to connect from a jack on the cards to the external audio input on a system with a sound card or integrated sound functionality. After you install the Hollywood Plus or NetStream software, you have to calibrate your display to work with the software. Using the Auto Calibrate option in the Configuration menu lets you calibrate your display in less than 10 seconds.

After I installed the Hollywood Plus card on the DeskPro EN, it worked flawlessly. I read MPEG-2 files from a Panasonic DVD-ROM and viewed them from a file on my hard disk. In addition to the normal play, rewind, fast forward, pause, and stop options, the software offered aspect-ratio control, password-protected content ratings (i.e., G, PG, PG-13, NC-17, and R), and about 100 language choices that ranged from Abkhazian to Zulu. A feature unique to this product is the ability to create a playlist that contains numerous MPEG files for viewing a sequence of material, whether the material is on a DVD disc or a hard disk file. The Hollywood Plus card doesn’t offer an option to play a file across a network.

Sigma Designs created the NetStream 2 card specifically for network use. The card supports Microsoft DirectShow, Microsoft ActiveMovie, media control interface (MCI) APIs and streaming, DVD-ROM, VGA and TV playback in 24-bit (16.8 million) color, .wav files, .rmi files, .mid files, audio compact discs, and .avi files. This card doesn't have the hardware compatibility troubles of the Hollywood Plus—it ran in all five previously mentioned machines I installed it in. However, the card didn’t run well in the dual-processor systems. In these machines, the MPEG stream became distorted; the sound periodically dropped out; and occasionally the system froze, which forced me to perform a cold boot. Therefore, I don’t recommend running the NetStream 2 in dual-boot processor systems until Sigma Designs optimizes the card for multiprocessor systems.

After I installed the NetStream 2 in a single-processor system, I played a 40MB MPEG-2 file (i.e., 1 minute of recording time) across a 10Mbps Ethernet network connection. This presentation used only 30 percent of the 166MHz Pentium processor’s resources and produced a fluid video presentation. If you want to use the NetStream 2 as part of a Video on Demand (VoD) solution for your network, the card supports numerous solutions, including Microsoft NetShow Theater Server, Oracle’s Video Server, Silicon Graphics’ Media Base, InfoValue’s QuickVideo, First Virtual’s VCache and VCaster, and Vsoft’s VideoClick.

Sigma Designs created MPEG-2 decoding cards to let you decode DVD-ROM based content and network content. If you install these cards on systems that support each card’s hardware recommendations, you can take advantage of the many features they have to offer.

PrimeView NS Model 325
On the other end of the MPEG-2 spectrum are products that can encode MPEG-2 content. Last year, products in this exclusive market cost roughly $20,000—and that price included only an MPEG-2 encoding card. FutureTel’s PrimeView NS Model 325 MPEG-2 encoder card offers this costly technology at a significantly lower price.

The PrimeView NS card supports multiple MPEG-2 encoding cards in one system, MPEG-1 and MPEG-2 encoding, and the ability to use a DirectShow-compliant reader to simultaneously decode and encode. However, if you want to encode a full-screen MPEG-2 stream and preview your work on the same system, you must install an MPEG-2 decoder, because the PrimeView NS Model 325 can’t decode an MPEG-2 stream.

Installation of the product’s hardware and software is painless. You pop the card into an open PCI slot and perform a normal software installation. On the back of the card are two audio RCA jacks, one RCA video jack, and an S-video input jack. I attached a video cable to the card and a VCR, and two cables to the encoding source for stereo sound. If the source from which you’ll be encoding has only a mono output jack, use a splitter to create two audio feeds from the mono jack to the PrimeView NS card. Although the splitter won’t give you stereo sound, by splitting the mono source into two feeds, you can take advantage of the codecs for stereo sound. These codecs are more advanced than the codecs for mono sound.

To encode MPEG-2 streams, I put a movie into the VCR and pressed play. A 1-minute MPEG-2 clip uses about 40MB of hard disk space, and the PrimeView NS Model 325 card can encode 1.8 Mbps to 15Mbps with constant or variable bit rates.

The product’s Recorder interface is straightforward and lists three available channels for encoding, which you can see in the bottom right corner of Screen 1. Each channel has a preview, record, play, and stop button. The toolbar has only File, Setup, and Help menus. The settings you need ―the Recorder and Parameters options―are in the Setup menu.

The Recorder option lets you Record to file, Record with preview, and select a software (i.e., MPEG-1) DirectShow decoder or hardware decoder. As I stated, if you don’t have an MPEG-2 decoder installed in your system, you can't access the last two options. The Recorder option also offers a Setup Parameters button, which takes you to the same window that the Setup menu’s Parameters option takes you—the Encoder Properties window.

In the Encoder Properties window, you can adjust the bit rate at which you want to encode material, and you can choose between creating MPEG-1 or MPEG-2 content. If you don’t need the full MPEG encoding capability, you can choose audio only content, video only content, or both. In addition, you can determine the reference distance for Group of Pictures (GOPs) parameters, determine the size of GOPs, you can enable automatic-scene change detection, and you can enable the creation of a new GOP if the software detects a scene change. In this window, you choose your input source and the horizontal resolution for which the product optimizes your encoded output. You can also find controls for modifying color, brightness, contrast, saturation, hue, and audio settings.

In addition to creating MPEG-2 content for DVD-ROMs, the PrimeView NS card is compatible with numerous network video distribution platforms, including Cisco’s IP/TV, IBM’s VideoCharger, InfoValue's QVS, FVC.Com’s Icast, and PictureTel’s StarCast. The product’s many options require a minimal learning curve, and the PrimeView NS Model 325 card doesn’t support multiprocessor systems. However, its easy installation, ready compatibility, and reasonable pricing structure make this product an attractive MPEG-encoding solution.