Saturday, 22 August 2015

I’m not ready for the 4k future.

Ultra HD is a confusing confection of standards, and is getting in the way of watching amazing 4k TV.

I want a new TV. It’s not that my current TV isn’t any good – the pictures are crisp, and the screen is large enough – it’s just that the new sets are even shinier. And the newest of the new TVs have the next super-duper feature – Ultra High Definition. Not just HD, but ULTRA. Sweet.

The problem is that the UHD future is still very uncertain. There are competing and non-interoperable technology decisions that will impact upon which TV I should choose – and getting the decision wrong could mean that I won’t be able to watch the programmes that I want to.

It’s content that drives behaviour that drives technology. This lesson has been applied with variable conviction through 3D, HD, widescreen, and NICAM stereo. In the UK today, Netflix, YouTube and Amazon Instant Video are already streaming content in 4k. BT has announced BT Sport UHD. The new UHD-capable SkyQ box is strongly rumoured to release before Christmas. Sony provides a 4k media hub – essentially a NAS pre-loaded with Sony 4k movies (and the Playstation original Powers) to provide content for your new Sony 4k TV. Samsung uses the same approach, but without its own movies. So the content is starting to emerge, to push the technology.

The first issue for the early-adopting consumer, is that UHD content will be limited and expensive. Netflix 4k needs a £8.99 per month subscription and the catalogue is limited to some flagship content from Netflix (House of Cards), AMC (Breaking Bad) and Sony back catalogue movies (Jerry Maguire). YouTube has a 4k quality setting and some 4k videos uploaded (beautiful pictures, chillout music, but very jerky and makes my laptop crash). Amazon Instant Video has some Amazon originals 4k content included in the prime subscription, and other back catalogue from Sony available to rent at £6.99 or buy at £18.99. You can bet the subscription hike from BT and Sky for 4k will cause a sharp intake of breath.

Once you’ve committed to spending on 4k, the second issue is that it may not play. To understand fully why, we need to unpick what UHD actually is.

UHD bundles together a whole set of advances in TV technologies. This bundling of advances makes UHD such a significant step forward. But because these are all individual steps, with no mandated correlation, there’s no guarantee that UHD means the same thing to all broadcasters and manufacturers.

First is the resolution: UHD is 3840 x 2160 pixels, which is four times the number of pixels as full HD. (Full 4k cinema is 4096 x 2160, which is slightly wider, as is currently the case.) UHD also allows for faster refresh rates, starting at 24 frames per second (current cinema rate), 25 fps (current TV rate), 30, 50, 60 and 120 fps. This promises a level of detail where the eye would have difficulty in seeing individual pixels, with no motion blur – at a cost of 20x current bandwidth.

Next up are the advances in colour reproduction. All current TVs use a mathematical representation of colour based on red-green-blue described by the standard Rec.709. Though this standard brought worldwide agreement on how colours (and white) should be represented, the range of possible colours is less than the range experienced by the human eye. To get close to human experience, UHD mandates the newer Rec.2020 standard.

To be able to describe colour more accurately, UHD allows for spending more bits to describe colour – 10 or 12 bits per sample rather than the current 8 = 1.5x current bandwidth. These are either sampled twice as frequently for brightness (luminance) than for red, and half again for blue (4:2:0), or twice as frequently for brightness than each of red and blue (4:2:2), or same frequency of samples for all three (4:4:4). 4:4:4 requires 2x the bandwidth as 4:2:0.

Brightness is also described more accurately using High Dynamic Resolution (HDR). HDR doesn’t necessarily increase the number of bits used to describe brightness, but how. Instead of the current mathematical Electro-Optical Transfer Function, a Perceptual Quantisation is preferred. This enables describing a wider dynamic range.

TVs currently go from 0.05 cd/m2 at black to 120 cd/m2 for full brightness.
The best-performing OLED TV goes from 0 cd/m2 to 800 cd/m2. HDR enables video to be described to take advantage of this available dynamic range – and more. The leading contender specification for HDR, Dolby Vision, claims an extra 20% bandwidth would be needed for metadata.

So we see that UHD = resolution + frame rate + colour gamut + sample rate + sub-sampling schema + HDR. Total bandwidth uplift would be 72x current bandwidth! Thankfully, there are new codecs that significantly reduce the bandwidth requirements. Both H.265 (HEVC) and Google VP9 promise 40% over current HD codec H.264, which was 40% improvement over MPEG2 as used in SD DTV broadcast. So use of HEVC or VP9 could reduce bandwidth uplift to 4.5x, but that still means bit rates of over 30Mbit/s.

However, the main reason why your content might not play is DRM. Studios are following the same tired old path of maximising the money they wring out of broadcasters and the public by the implementation restrictive DRM. However, there are a few contenders out there. Netflix and BT mandate Microsoft PlayReady. There are also solutions from Verimatrix and Nagra. Each DRM schema must be implemented in hardware (the current market leader is Broadcom with their Sage system-on-a-chip), so each DRM schema requires a different STB or TV.

The Samsung TV that is capable of playing Netflix 4k may not be capable of playing the UHD content from AcmeFutureTV if the DRM is different. And the studios focus heavily on DRM; there’s no guarantee that each studio will choose the same DRM vendors to approve. So different content may need different DRM and therefore a different STB. (I hope I have enough inputs on my TV.) The equation is now: UHD = DRM + codec + resolution + frame rate + colour gamut + sample rate + sub-sampling schema + HDR.

So before I buy my next TV, I should ask myself: is the TV full 4k or UHD1 resolution? Does it have a Broadcom Sage chip? Is it using the right DRM variant of the chip? Will I be connecting to the TV using HDMI 2.0? Does the output of the for the content STB support HDCP 2.2? Does the TV support Rec.2020 colour space? 10-bit/ 12-bit colour depth? 4:2:2 or 4:4:4 chroma sub-sampling schema? Does it have sufficient dynamic range to reproduce HDR? Does it have a frame refresh rate of 60 fps or even 120 fps? Does the player within your STB or smart TV support the HEVC or Google VP9 codec? And now that I’ve answered these questions for the TV, was the movie that I want to watch encoded with the right combination of PlayReady/ Rec.2020/ 12-bit/ 4:4:4/ 120fps/ HEVC?

Why should I, as a consumer care, when all I want to do is to watch a movie?

With all this variability in what makes up UHD, it’s understandable that some broadcasters are being cautious with their investment. They need to ensure that their network infrastructure can cope with additional bandwidth demand, invest in head ends to process content provider feeds into coherence, and invest in STB because Smart TVs are unlikely to be smart enough to cater for their particular combination that makes up UHD.

This caution allows OTT providers to lead the way with 4k. With no network investment to worry about, Netflix, YouTube, Amazon, Sony et al can focus investment on content and hardware. The approach is different in each case: Netflix has bet its farm on its tie-up with Broadcom, hoping that everyone will put the chip in their TV or STB to get Netflix, and it looks to have been a wise bet. Amazon develops its own STB, Sony its Smart TV and Playstation. YouTube does not have studio content licensed for 4k (though GoPro's Adventure of Life in 4k is arguably commercial content but with a free license) and is agnostic on hardware. 

Future-proofing my next TV purchase will probably be impossible. The panels to support Rec.2020 and Dolby Vision just aren’t made yet. However, 4k is gathering commercial momentum, so realising the full UHD1 spec in a TV will be irrelevant if I actually want to watch 4k content. I think it’ll be enough to have a 4k panel, and have lots of HDMI 2.0/ HDCP 2.2 connectors. However, I think I’ll have a cluster of STB around the base of my TV. It seems there’s no getting away from a rat’s nest of cables behind the TV.

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