Video encoder slims down for spring
-- EDN, January 18, 2001
With the New Year, many of you may have resolved to "lose a few pounds." Vweb has similar ambitions but with slender silicon rather than slender bodies in mind. Even though digital-video-recorder pioneer ReplayTVmight be now undergoing financial struggles, industrywide trends suggest there's a healthy market for various digital-video-capture, distribution, and time-shifting applications. Vweb hopes to be at the heart of systems targeting those applications.
The company's $30 (10,000) VW2000, now in production, encodes to D1 resolutions at a 2- to 15-Mbps constant bit rate, 500 kbps for SIF (source-input format) resolutions, and as low as 128 kbps for QSIF (quarter-source input format) (Picture). High-resolution encoding targets closed-box archiving—that is, digital VCR—and high-speed intranet-distribution applications, whereas lower resolution bit rates are more appropriate for Internet delivery. Vweb touts its part's 500,000-gate logic, which the company claims is one-half to one-fourth the size of competitive offerings. Key to the low gate count is Vweb's proprietary motion-estimation algorithm, whose hierarchical search techniques also promise better matches at a faster search. The product's firm-ware needs less than 15 kbytes of memory, which the company asserts is 10% the size that other vendors' products need. The VW2000 also requires only 4 Mbytes of external buffer memory, for which it embeds a 32-bit, 166-MHz SDRAM controller.
The VW2000's rate-control algorithm tracks 60 parameters, resulting in a more consistent group-of-pictures size and fewer disruptive I-pictures. For those who prefer to let Vweb do some of the system work for you, two production-ready board designs are available. The PCI-based, $800 (1000) VW2KWIN1 includes a separate MPEG audio encoder and relies on a PC-host CPU running Windows 98 or 2000 for control, whereas the stand-alone $1000 (1000) VW2KEMB1 includes a MIPS control CPU and serializer. Both boards accept composite or S-Video and dual-channel analog audio. Both cards output MPEG-2 elementary and packetized elementary streams; the VW2KEMB1 adds support for MPEG-2 transport streams.
Vweb's chip is low-cost, particularly when you consider the low-density and low-cost external-DRAM requirements, at least until 16-Mbit DRAMs become rare chips. However, it is a video-only, encode-only architecture. Other companies targeting MPEG-2 applications include Stream Machine, GlobeSpan, Equator Technologies, and C-Cube (www.streammachine.com, www.globespan.net, www.equator.com, www.c-cube.com). Stream Machine's SM2201 can both encode and decode video, but not simultaneously (see "Get maximum pics with minimum bits," EDN, Dec 23, 1999, pg 16), whereas iCompression's iTVC15, now marketed by acquiring company Globespan, simultaneously encodes and decodes both audio and video (see "Audio and video, decoding and encoding...," EDN, May 11, 2000, pg 28). Vweb's upcoming VW2010, due to become available for sampling in the second quarter, will offer similar capabilities, and future chips will target MPEG-4.
C-Cube's similarly priced DVxcel is also a video-only chip, but it simultaneously encodes and decodes (see "Cost-compressed codec targets VCRs," EDN, Feb 3, 2000, pg 26). C-Cube's $29 published price, however, requires a significantly larger order quantity than does Vweb. Media processors, such as Equator Technologies' MAPCA-2000 claim, at least in their controlled-environment demos, to be able to tackle encoding, decoding, and system-control functions in a single chip (see "Compression puts images on a diet," EDN, June 18, 1998, pg 71). Media processors can also support nonstandard codecs, such as wavelets (see "Wavelets both implode and explode images," EDN, Dec 21, 2000, pg 55), but you may not need or be willing to pay for that flexibility.
Vweb, 1-408-615-1888, www.vwebcorp.com.
—by Brian Dipert
