San Jose, Calif. -- Video has hit an impasse on the road to the digital home. This summer, separate groups of engineers will finish work on two incompatible display interfaces--DisplayPort and the Unified Display Interface--vying to become the standard for a secure digital link in consumer systems and computers. The pair will compete against two digital interfaces already in use--DVI and HDMI.

Thus far, no formal talks are scheduled among advocates of the new interfaces, and no one knows just how the competition will shake out. The confusion reflects unresolved conflicts among security, interoperability, ease of use and low cost at a time when the transition from analog to digital media is still in its formative stage.

"We've ended up with a nightmare scenario of multiple standards. It's a frightening mess," said Bob O'Don- nell, vice president of clients and displays at International Data Corp. (Framingham, Mass.). "The notion of a converged display interface may just go away."

But "this is a transition period," said Michael Ep- stein, a manager of technology and standards for Philips Intellectual Property and Standards, so "everything may not be neat and clean." Epstein is finishing a content protection approach for DisplayPort that has the latest security features content owners want, but it will not work with the scheme used in today's Digital Visual Interface (DVI) and High Definition Multimedia Interface (HDMI). "It's not clear there's an immediate need for interoperability," said Epstein, given that shipments of DVI and HDMI are still relatively low and the transition to digital still young.

The Unified Display Interface (UDI) uses the same form of content protection found in DVI and HDMI. But it lacks features, such as longer encryption keys and proximity restrictions, that content owners want to see in next-generation systems.

"Everyone would agree having two [new] standards is not desirable. Before products become integrated [into chip sets in two or three years], we expect to resolve this--but I don't know how," said Simon Ellis, UDI program manager at Intel Corp.

All sides agree on the underlying need to shave costs and broaden interoperability. Thus they want a single, royalty-free technology that could replace low-voltage differential signaling (LVDS) inside notebooks, supplant VGA in computers and displays, and link to digital TVs, set-top boxes and other consumer gear. Content owners fear those older, unsecured interfaces will put their movies and TV shows at risk of illegal copying, so digital security to plug this "analog hole" is a key motivation,.

"Analog VGA has been the PC standard for 20 years, but now we are seeing some pressure for all content to be protected, and we can't do that on an analog interface," said Bob Myers, who co-chairs the DisplayPort effort and manages a display technology group at Hewlett-Packard Co. "At some point, we will have dates by which we need to support copy protection."

According to In-Stat Inc., DVI shipped in more than 60 million systems, mainly PCs and peripherals, last year, while HDMI went into fewer than 20 million systems, mainly digital TVs and set-top boxes. But the two are expected to hit parity this year as DVI, which dates back to 1998, peaks and HDMI--created in 2002--surges.

As early as 2003, a group of PC makers, including Dell and HP, were chafing at HDMI's technical limits and royalty structure. The charge is roughly 4 cents per system, plus a membership fee that typically runs $15,000 a year. They developed DisplayPort as a royalty-free option designed to leapfrog HDMI and DVI on several fronts.

DisplayPort taps the electrical layer of today's 2.5-Gbit/s PCI Express bus and rides its coattails to bandwidth of up to 10.8 Gbits/s over four channels. It also delivers a new and improved copy protection scheme. DisplayPort uses a 128-bit encryption key along with AES, rather than the 40-bit key used in the high-bandwidth digital content protection (HDCP) spec. It adds support for checking the proximity of the transmitter and receiver, a new technique to ensure users aren't fooling a system to send content out to distant, unauthorized users.

The copy protection scheme will not hit a 1.0 draft until later this summer. Then it must go through approval processes at various content organizations, such as the Advanced Access Content System, which oversees content protection for next-generation DVDs.