Russ Lockwood
When designing multimedia PCs, systems engineers face a number of factors that conspire to make digital-video-capable PCs pricey while limiting their digital-video playback to quite unexciting, often postage-stamp-size movies. The price problem is due to a duplication of components in which PCs have two RAMDACs; two frame buffers; and two controllers, one each for video and graphics. The small-size movies and dropped frames are caused by architectures that can't transfer video at a fast enough rate.
Two coalitions offer new graphics standards to speed digital video across the desktop. The first, VESA (Video Electronics Standards Association), offers two solutions: VAFC (VESA Advanced Feature Connector) and VMC (VESA Media Channel). The other coalition, an Intel-ATI
pairing, offers SFBI (Shared Frame Buffer Interconnect).
All three standards will require new graphics board designs and associated drivers to implement their promised speed boost. These new boards will plug into ISA, EISA, VL-Bus, PCI (Peripheral Component Interconnect), or Micro Channel slots. The first boards for VL-Bus and PCI are expected to be announced by the time you read this.
VAFC is a 32-bit replacement for the old and sadly out-of-date 8-bit VGA connector. While the old VGA feature connector supported a video in a window with a resolution of only 640 by 480 pixels and 8-bit color, VAFC supports video at much higher resolutions and in better color (up to 1024 by 768 pixels at 256 colors with a 75-Hz refresh rate).
VMC, like VAFC, offers a 32-bit data path. But VMC supports up to 15 video streams simultaneously and offers a more long-term solution for video computing than VAFC. One developer described VMC as "a video superhighway that bypasses the already-crowded system bus." S
ince VMC is a dedicated channel for real-time video, peripherals can communicate independently and without slowing the system CPU. VMC decouples the memory subsystem from the video transfer specification, allowing graphics board manufacturers to offer a variety of boards with differing types of graphics memory--DRAM, VRAM (video RAM), synchronous DRAM, RAMBUS, and other future memory standards.
Hossein Yassaie, vice president of engineering for VideoLogic, says that adding VMC capabilities to a system increases the cost to the consumer by $10 to $30. He adds that the cost to add videoconferencing hardware to a VMC-equipped system would be about $600, compared to the $3000 or so that the hardware costs today.
Intel-ATI's SFBI combines frame buffers and memory used by each multimedia subsystem into a single, shared memory pool of up to 8 MB, with a protocol for arbitrating among devices attempting to tap into that memory. The design goal is to keep all components on one board while reducing board
cost by eliminating duplicated memory among multiple devices. However, unlike VMC, SFBI currently mandates using either VRAM or DRAM.
SFBI is faster than VAFC and VMC, offering a top-end transfer rate of 200 MBps, but that rate is for a 64-bit data-path implementation. In 32-bit mode, SFBI offers closer to 100-MBps data transfer. To tweak the speed further, SFBI includes SynchroLink, a channel that coordinates video and sound sources without accessing the host processor.
Although the SFBI scheme provides no external feature connector, you can connect an SFBI card to another SFBI card over the host bus or, if you have an interface on the SFBI card that can connect to a VMC or VAFC card, you can connect the two cards that way. Indeed, Don Fraser, ATI product manager of video components, contends SFBI complements, rather than competes with, VAFC and VMC.
At press time, three companies had announced boards that are based on one of the new standards and illustrate the benefits of these new vid
eo architectures. For example, Matrox's $649 MGA Ultima-VAFC for PCI allows video playback at resolutions of 1280 by 1024 pixels at 30 frames per second. Matrox (514) 685-2630) plans to introduce the MGA Video-Pro, a PAL and NTSC video-encoding board with a VAFC connector, in the second quarter of this year.
ATI's Video-It video-capture board offers real-time compression of video from a camcorder or a VCR, as well as live video in a window display at any resolution. ATI ((905) 882-2600) says it will release Video-It in mid-April for $499.
VideoLogic's 928Movie (from $349), a multimedia accelerator board developed jointly with IBM, combines graphics acceleration with VideoLogic's custom ASIC PowerPlay Digital Movie Accelerator. VMC add-ins from VideoLogic ((617) 494-0530) for MPEG video capture and playback are scheduled for release in the second quarter of this year.
Other vendors are sure to release board products throughout the year.
Video Fast-Lane Lineup
VE
SA Advanced Feature Connector
A short-term solution for video overlay in high-resolution graphics modes
150-MBps transfer rate
Eliminates RAMDAC duplication
No shared frame buffer
N/A
VESA Media Channel
A separate channel that merges graphics and video
Maximum 132 MBps in 32-bit mode
Eliminates RAMDAC, frame-buffer duplication
Designed for current and future RAM technologies
Supports any codec
Frame Buffer Interconnnect
Predominantly a single-card solution; merges graphics and video
Up to 200 MBps in 64-bit configuration
Eliminates RAMDAC, frame-buffer duplication
RAM and DRAM only
Currently supports Indeo codec only
Illustration: A feature connector lets peripherals such as graphics and video cards communicate and share information over cables.
Video Acceleration in the Fast Lane
