MPEG-4 Videos On Older Computers
Most video enthusiasts are all too aware of the fact that you can only play films in MPEG-4 or Divx format in full-screen mode smoothly by using a powerful PC system. So what’s the point in spending entire days downloading a long-awaited movie from the Internet, only to find you can’t even play it properly? After all, not everyone has a high-speed processor with a high clock speed. To ensure that just about any Divx film can be played back without image dropouts, you should use at least an AMD Athlon with 800 MHz plus or an Intel Pentium III/733. Otherwise, you will very soon encounter image gremlins or errors, particularly if the image content is complex with numerous motion vectors. Videos with action scenes are good examples of this.
The packaging for the decoder board from Sigma Designs.
The first MPEG-4 hardware decoder: PCI card with Realmagic EM8475 chip.
Contents of Sigma Design’s Package
Package from Sigma Designs contains Realmagic Xcard, cables and remote control.
Interested users can acquire the complete decoder package for $99. The package includes the PCI card from Sigma Designs, which is based on the EM8475 decoder chip from Realmagic. The producer has also thrown in a loop cable, which you will need if you intend to play videos on your computer monitor. Otherwise, the card is designed for output on a television set. Numerous cables go to complete what is quite an impressive set of equipment, which also includes an S-VHS to cinch adapter, a cinch extension, an S-VHS to RGB adapter, plus two audio cables with jack and cinch connectors. The software supplied with the CD-ROM essentially consists of the video player along with the drivers. A touch of convenience is provided by the infrared remote control, which boasts high-end equipment features. The transmitter is operated via the serial port of the PC. State-of-the-art boards such as the Abit AT7 with a VIA KT333 chipset no longer have COM ports, meaning that this function is not available for these models.
Numerous cables are included along with the actual hardware decoder.
User-friendly control — the supplied remote control with an infrared transmit module for connection to the serial port.
Comparison of the various chips in the EM84x series from Realmagic.
Optional SCART cable for connecting a video recorder.
Installation: Loop cable for VGA
The decoder board integrated inside a computer system.
It takes about ten minutes to get the decoder board up and running. This requires opening the computer and inserting the board in an available PCI slot. After that, you connect the loop cable, which establishes a direct connection to the graphics card, permitting video output via the computer monitor as well. Now to explain: the VGA output signal from the graphics card is routed through the decoder board. Otherwise, it is only possible for the video signal to be depicted externally on a television set, for example. The solution involving the «loop cable» harkens back to the earlier days of the Voodoo cards from 3Dfx, which does mean, unfortunately, that this technology reduces the display quality, particularly at high resolutions and frame rates. Once the board has been installed in the computer, you install the drivers and software from the supplied CD-ROM or floppy disk (for the remote control).
Slight criticism can, however, be leveled at the operating instructions, which are rather meager and provided on a leaflet: a better-illustrated set of instructions would greatly simplify the installation procedure.
The Decoder Ports — Video And Audio
View of the ports on the decoder board from Sigma Designs.
On the front panel, Sigma Designs has incorporated a VGA input and output for the loop cable, in addition to a TV-out port (S-VHS) and audio outputs (analog and digital). Furthermore, the board also features the following ports: a connector strip for SCART audio/ video; a feature connector (digital video out); an analog audio output port for the internal connection to the sound card and digital inputs/ outputs (SP/DIF) for audio. The solution involving the loop cable seems slightly antiquated, since conventional TV cards use a Conexant chip, which writes the data directly via the PCI bus into the graphics card’s memory. The solution from Sigma Designs does offer one advantage, however — the PCI bus is not overloaded, thus avoiding problems, particularly with older computers. The manufacturer also cuts costs with this solution.
Supported Video Formats: MPEG-1, MPEG-2 and MPEG-4
Error message for video formats that are not supported.
Supplied player software for playing back MPEG video (DVD and video CD).
Although the decoder card is advertised as the «first board for playing MPEG-4,» it is also suitable for playing MPEG-1 and MPEG-2 sequences. DVD films can also be played with relative ease from a corresponding DVD drive.
A distinction should be made regarding the different Divx codecs: only films using version 4.02 or higher of the Divx codec are supported by the Sigma Designs decoder. In our test field, the recently launched Divx 5.02 codec did not present any problems.
The video display window can be scaled variably.
Customization options for the video window.
The video player’s audio menu.
CPU Load — 10% With Duron 650
CPU usage at 10%, in conjunction with an AMD Duron 650 under Windows XP.
The use of the hardware accelerator makes a noticeable difference, especially with older PC systems with less CPU power. The system we used in our tests with an AMD Duron 650 exhibited an average CPU load of 80% — i.e., when using the media player from Microsoft under Windows XP and a special MPEG-4 test sequence. By using the decoder board, the processor load fell to an average of 10% to 12%.
The EM8475 decoder chip’s mode of operation
Schematic diagram of the EM8475 decoder chip.
The graphic illustration above schematically depicts the structure of the MPEG hardware decoder from Sigma Designs: essentially, the board is based on the EM8475 chip from Realmagic — a highly integrated DSP processor for MPEG decoding. The chip also contains the PCI controller and the control unit for the memory interface, the board with 4 MB cache memory being equipped with 7 ns access time. The memory clock speed is 133 MHz.
Test Sequences Via TV And Monitor Display
This picture shows the quality of the TV output. The picture is interference free and razor sharp.
Even the full-screen display on a computer monitor can be quite impressive.
Conclusion: Convenient MPEG-4 Playback For Dated Computers
With its Xcard, Sigma Designs is the first producer to supply a hardware decoder for MPEG-4. This means that older computers with less processor speed especially stand to gain from this solution. Even with an Intel Pentium II/300 it is now possible to play a Divx-MPEG-4 film in full-screen mode smoothly. In addition to playing MPEG-4 films, it also lets you play DVD videos in MPEG-2 format and Video CDs in MPEG-1 format without overloading the CPU. It is even possible to play your favorite film via the TV output, while running an office application at the same time. The Sigma Designs package, which is available for the price of $99, comes with plenty of cables, thus catering to virtually all the needs of the average user. Also worth mentioning is the remote control provided with the board, which communicates with an infrared module via the serial port. The awkward player software is a point of criticism, however — it has no intuitive user controls and it takes a long time to figure out the available functions. The EM8475 chip from Realmagic, which is integrated on the decoder board, is the first module in its class. Accordingly, it remains to be seen as to whether or not some set-top boxes will be equipped with this chip in the near future. All in all, this is a good product that is ideal for users with older PCs.
