Last week, I attended a webinar hosted by CEDIA (Custom Electronics Design and Installation Association) called "HDMI 2.0: A Look Into the Standard." The presenters were Steve Venuti, President of HDMI LLC; Jeff Park, Technical Specification Manager of HDMI, LLC; and Michael Heiss, CE industry consultant and jolly-good CEDIA Fellow as well as chair of the CEDIA Technology Council.I didn't learn much that I don't already know, but it was a good reminder that the version number doesn't mean much other than a list of possible features that manufacturers might or might not implement. That's why HDMI Licensing wants companies to indicate what HDMI features they have included in their products rather than simply touting "HDMI 2.0." That number refers only to the specification that defines what features are supported, not what must be implemented.HDMI 2.0 ups the maximum bandwidth from 10.2 gigabits per second to 18 Gbps, which can be carried on existing high-speed HDMI-certified cables. However, extenders, boosters, and any other electronics in the HDMI signal chain—including Redmere booster chips and HDBaseT—probably can't support that bitrate without a hardware upgrade.The increase in bandwidth is made possible by a new, more efficient signaling method. Even better, the interface uses the previous signaling method for traffic below 10.2 Gbps, then kicks in the new signaling above that, which means it's completely backward compatible with HDMI 1.4 devices.New features supported by HDMI 2.0 include the ability to transmit 4K video at 50 and 60 frames per second (with some limitations, which I'll get to in a moment) and up to 32 channels of audio with a sample rate up to 1536 kHz. Also, new commands have been added to CEC (Consumer Electronics Control, the ability to control multiple connected devices from one remote), and all commands must be implemented rather than being optional as in previous versions—a welcome requirement even if it flies in the face of HDMI's otherwise feature-optional paradigm. Other features include support for the Rec.2020 color space, dual viewing (two programs displayed on the same TV and isolated for each viewer with glasses, much like 3D), multi-stream audio, dynamic auto lip-sync, and the 21:9 aspect ratio.As I said earlier, HDMI 2.0 can handle 4K/UHD at 50 and 60 frames per second, but there are some limitations—in particular, in the bit depth and level of color subsampling it can convey. For those who are unfamiliar with color subsampling, it's a type of data compression in which some color pixels are discarded from a component-video signal and reconstructed by the display. It's specified as a series of three numbers—the most common schemes are 4:4:4, 4:2:2, and 4:2:0. Because color subsampling applies to component-video signals, the first number refers to the black-and-white pixels, while the second and third numbers refer to the color-difference pixels.With 4:4:4, no color pixels are discarded, while 4:2:2 discards half the color pixels, and 4:2:0 discards 75% of the color pixels, which reduces storage and transmission-bandwidth requirements. However, the less color subsampling that is used, the better the image quality, especially in terms of clean transitions between colors. Amazingly, Blu-ray uses 4:2:0 and still manages to achieve great picture quality.Using 4:2:0 color subsampling, HDMI 2.0 can convey 4K/UHD at 50/60 fps with up to 16 bits of resolution per color. This provides tremendous dynamic range—far more than the current HD system, which uses 8-bit resolution. If the color subsampling is 4:2:2, HDMI 2.0 can accommodate up to 12 bits of resolution for 4K/UHD at 50/60 fps. And at 4:4:4, HDMI 2.0 is limited to 8 bits for 4K/UHD at 50/60 fps. This presents a conundrum for video-content creators and consumers, who want the best possible specs all around.I suspect—hope, actually—that the UHD system will settle on 4:2:2 at 12-bit resolution, but that is far from certain at this point. A resolution greater than 8 bits is critical to support a higher dynamic range without visible banding, which is even more important than the increased number of pixels in my opinion. And less-aggressive color subsampling will yield sharper transitions between colors.HDMI 2.0 also supports the Rec.2020 specification, which includes a much wider color gamut than the current Rec.709. This allows content and displays to accurately reproduce many more colors than today's Blu-rays and HDTVs.Many people ask me about alternatives to HDMI—in particular, DisplayPort. As you can see in the following table, DisplayPort 1.2 does offer a somewhat higher overall bandwidth than HDMI 2.0, and much higher Ethernet bandwidth. It also transmits some power and USB communications. DisplayPort is common in the world of computers, but HDMI is so entrenched in the consumer-electronics industry that I doubt it will ever be replaced by DisplayPort. HDBaseT also carries power and USB along with HDMI signals, but its overall bandwidth is the same as HDMI 1.4 until its hardware is upgraded.The bottom line is that the term "HDMI 2.0" means next to nothing when trying to figure out the specific capabilities of a particular piece of gear. It's up to consumers to discover which features a manufacturer has included in its products, which can be added in a firmware update, and which will never be implemented. Hopefully, manufacturers will start explicitly listing the features they include in each product, making it easier for consumers to select the gear that's right for them.