HD and Beyond: An Introduction to HDMI 2.0
By David Meyer, Kordz.
Each time a new version of HDMI is announced, there follows a buzz of new features and formats, but also a groa...
By David Meyer, Kordz.
Each time a new version of HDMI is announced, there follows a buzz of new features and formats, but also a groan from the custom installation community as to what the implications may be. HDMI 2.0 paves the way for some fantastic new video and audio capabilities, but there's no need to panic - the changes may not run as deep as you might think. Ultimately HDMI 2.0 will settle into a place of normality, as has happened with every iteration before it.
So what does HDMI 2.0 offer, how is it different, and what are the headline features that you need to know about? Let's take a look.
Development of HDMI 2.0
HDMI 2.0 is the first major HDMI specification release since version 1.4 back in 2009, so it's fair to say that a lot has changed, and it needs to. There are now two HDMI organisations:
• HDMI Licensing LLC with its seven founder companies. Developers and managers of the HDMI 1.x generations, and now also appointed as the licensing, marketing and compliance managers of HDMI 2.0.
• HDMI Forum Inc. a non-profit corporation founded in 2011, with more than 80 member companies for broader market development of future versions of HDMI.
An important point to note is that HDMI 1.4b remains as an ongoing specification, with HDMI 2.0 running concurrently with its subset of additional optional features and enhancements. Existing HDMI Adopters do not automatically get an upgrade; they must sign an addendum and be accepted before they can become adopters of HDMI 2.0.
Key Features of HDMI 2.0
The following is a summary of some of the key new features of HDMI 2.0:
[caption id="attachment_4516" align="aligncenter" width="600"] Summary of some of the key new features of HDMI 2.0.[/caption]
In this article we'll focus on 2160p, and touch on anamorphic. We'll be coming back to explore audio next month.
Emerging Trends - 4K TV Firmware Upgrade to HDMI 2.0
The first key new feature of HDMI 2.0 out of the gate is the upgrade of 2160p (4K) to 60 frames per second within the existing defined HDMI bandwidth, where previously under HDMI 1.4 it was limited to 30fps. Both Sony and Panasonic have recently announced firmware updates for their existing 4K TVs to enable this feature, indicating that there is no new hardware (aka 'speed') required. As an aside, they tend to tout this upgrade as 'HDMI 2.0', but that's a non-compliant practice as it is actually just one of a multitude of new features of HDMI 2.0 that they're talking about. What they really mean is that the firmware just adds newly-defined support of 2160p/60, 8-bit 4:2:0... assuming the existence of content.
So how is it possible to double the frame rate without doubling the bandwidth? The answer lies in the '8-bit 4:2:0' reference; save on colour data, give back in frame rate.
Chroma Subsampling and Pixel Data Packing
Chroma subsampling is a process of compressing, or rather stripping out colour data to reduce file size and/or video transmission bandwidth load. The premise is that the human eye is far less sensitive to colour than it is to brightness and greyscale - by a factor of 20, in fact. As such, the amount of colour information in video can potentially be reduced without us really noticing... or that's the plan.
The trick is to leave the resolution and greyscale untouched, which is why it is only applicable to component video (YCbCr) signalling, where the separate luminance (Y) channel can be left intact. The most common chroma subsampling methodologies are 4:2:2 with half colour data when compared to 4:4:4 original, and then there's 4:2:0, as used with DVD and Blu-ray, with just one quarter of the original colour data.
The sampling commonly occurs over a 2x2 pixel array, where each pixel comprises a luminance channel (Y) and two chrominance channels (Cb and Cr). Figure 1 below shows a simplified depiction of the uncompressed array before any subsampling, called 4:4:4.
Figure 2 shows how HDMI 1.4 (and prior) handles YCbCr, where everything from 8-bit 4:2:0 to 12-bit 4:2:2 produces precisely the same bandwidth at a constant 96 bits per array (the same as 8-bit 4:4:4). Figure 3 depicts 4:2:0 as it really should be, being how HDMI 2.0 handles it; with 8 bits of 'Y' per pixel, and just one of each 8-bit colour component Cb and Cr across the whole 2x2 array.
[caption id="attachment_4520" align="aligncenter" width="600"] Representation of 8-bit 4:4:4 sampling (Fig 1); 8/10/12-bit 4:2:0 and 4:2:2 sampling under HDMI 1.4 (Fig 2); and 8-bit 4:2:0 sampling under HDMI 2.0 (Fig 3)[/caption]
What they've done with HDMI 2.0 is recognise that 8-bit 4:2:0 natively nets 48 bits per sample array, and they've actually passed on the savings. That is, they halve the bandwidth, which enables them to then double it again with frame rate. Voila - 30fps goes to 60fps in the same bandwidth as before. Note that this is ONLY applicable to 8-bit 4:2:0. This is not where HDMI 2.0 stops - there are even better formats on the horizon.
HDMI 2.0 Need for Speed
There are several formats of 2160p (4K) that are included in the HDMI 1.4 specification, all of which run at 8.91Gbps, the specification then capping out at 10.2Gbps. HDMI 2.0 introduces some more at this legacy level, and several superior combinations at double this rate, being 17.82Gbps (rounded to 18Gbps, 6Gbps/ch). This is well beyond the limits of HDMI 1.4, and defines the top end of HDMI 2.0. The range above 10.2Gbps is referred to as 'HDMI 2.0 mode', whereby the TMDS (Transition Minimised Differential Signalling) clock is slowed to 1/40th of the data rate to counter the effects of EMI (ElectroMagnetic Interference) at such high speeds. Other techniques such as data scrambling are also employed to improve stability.
HDMI 2.0 Cables
Right off the bat - THERE IS NO SUCH THING! If anyone offers you so-called 'HDMI 2.0 cables', turn and run. It will be either a marketing tactic, or expression of ignorance. Either way it is non-compliant. When the HDMI 2.0 specification was first announced, it was accompanied by this statement;
[caption id="attachment_4515" align="aligncenter" width="600"] Excerpt from HDMI Licensing, LLC, Press Release, 4 Sep 2013.[/caption]
There is no new speed, no new cable. Does it make sense that a cable rated to 10.2Gbps can then carry up to 18Gbps? Logically no, but they have some tricks up their sleeve. 2.0 introduces a parametric-like new sink EQ system which is supposed to make a 10.2Gbps-tested cable perform up to 18Gbps. It can't however, fully compensate for the collapsing effect of cable length, and will be expected to cap out at around 3m with a decent cable. Beyond that, it's all bets off and there is no new cable speed specification or directive. My prediction: HDMI cables will have to turn active, as some already have.
Another fantastic feature of HDMI 2.0 is its ability to support different pixel aspect ratios, namely 4:3 - which is nothing to do with 4:3 TV, by the way. For example, a 1080p image comprises 1920 pixels wide and 1080 pixels high. Every pixel is square, so content is fed to each pixel in 1:1 ratio. The array of 1:1 pixels then determines overall image aspect ratio, being 1.78:1, or 16:9.
What HDMI 2.0 has introduced is the ability for content to be formatted using 4:3 pixel ratio. Every pixel in a supporting display could potentially be fed 4:3 anamorphic content, even though the pixel is still 1:1 square. In practice, a projector with a matching anamorphic lens will horizontally stretch the image by 1/3 (4:3). The result is 2.37:1 picture aspect ratio (1.78/3)x4 = 2.37.
No more encoded black bars. It means we can look forward to maximising image resolution for cinemascope 2.37:1 in a standardised format.
HDMI 2.0 brings many benefits and some exciting new features, paving the way for a level of AV immersion the likes of which we have never seen. Yes, it means new hardware, but that points to opportunity for the custom AV dealer/installer. HDMI speeds are ever-increasing, and that means more demand on quality infrastructure to ensure everything works as planned.
Imagine a premium 2160p/60 2.37:1 aspect home cinema projection system with brilliant 12-bit 4:2:2 colour and 10.2 audio system. How about dual-view gaming with two players, each experiencing their own full-screen 1080p image on the same TV, with separate audio tracks being fed to their headphones. Or to really make your head spin, imagine an IMAX Private Theatre with 30.2 channel 3D digital sound. Phwoah!
David Meyer is the Founder and Managing Director of Kordz, specialist in reliable long-reach HDMI. Following the launch of HDMI 2.0 at IFA in Berlin in September 2013, Kordz became the first approved HDMI 2.0 Adopter in the world, outside of the HDMI Forum.
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