Sorting the Standards
HD over coax is a catch-all for four technologies that enable the transmission of HD video signals over coaxial cable. These are: high-definition serial data interface (HD-SDI); HD composite video interface (HDCVI); HD transport video interface (HD-TVI); and analog HD (AHD). All are currently in use for video surveillance equipment and while some are more popular than others, there is no indication that one or more will emerge as an overarching, industry-wide HDoC standard.
The granddaddy of these is HD-SDI, which has fallen behind other standards in recent years.
“HD-SDI is an old standard that has been used by broadcasters for a long time. It’s actually one of my favorite standards because the picture is as good as anything,” says Hanwha Techwin America’s Robert Wegner. “Some companies, including us, tried to make products for the security industry but not very successfully because the products were too expensive. That’s when they looked to other standards.”
However, all of the standards are fairly solid, he adds.
“They all have advantages and disadvantages, but there’s very little difference. I would say if you put three monitors next to each other and one is running AHD, another is running CVI, and another is running TVI — and they’re all playing on the same field, say, 1080p at 30 frames a second — you’re probably not going to be able to see a difference,” Wegner says. “On paper, of course, they have differences, but they’re pretty good — they’re very similar.”
The decision of which of the standards to employ relies largely on what the manufacturer has decided to use in its products. And the capabilities of those products is as important as, if not more important than, the chosen standard itself, Wegner says.
“It’s really a preference. It’s a choice and it’s more about what comes before the standard that is connected to coax. I think that’s more important than the actual standard,” he says. ”We can already do four megapixel on AHD, and soon you’re going to see 4K on AHD. It’s coming, and it’s already out there.”
In many ways, manufacturers’ standard(s) of choice come down to licensing cost and complexity.
“To me, this goes to the ownership of the standards. I think that what we refer to as HD-Analog (AHD) is the least restrictive in terms of limiting use via the cost of licensing,” says Digital Watchdog’s Mark Espenschied. “The specs of the standards are similar and people seem to argue for their favorite. There is a little difference in the length of the run, but again, similar. I think what used to be a significant issue is now a generic issue with people expecting all three standards to be supported by the camera or DVR.”
At present, there are two standards that have risen to the top, believes North American Cable’s Aaron Starr.