Yesterday the Blu-ray Disc Association formally completed the Ultra HD Blu-ray specification. The specification has been under development for some time, with the first information about it being released in September of last year. The new specification allows for higher resolutions, a greater range of colors, and larger capacity disks in order to store a new generation of Ultra HD content.

The biggest point of the new Ultra HD Blu-ray specification lies in its name. Ultra HD Blu-ray will support the 3840x2160 Ultra HD resolution that has become standard across so called "4K" or Ultra HD televisions. That being said, an increase in resolution is not the only important part of the Ultra HD Blu-ray spec. The Ultra HD content standard, more accurately known as BT.2020, defines various aspects that go beyond resolution, including color gamut, color bit depth, and frame rate.

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In my view, the most important aspect of the BT. 2020 standard is the use of the Rec. 2020 color gamut. The color gamut that has been used for basically all picture and video content for quite some time now is called Rec. 709 or sRGB. sRGB is actually quite a narrow gamut, and has an lower overall number of colors than even the NTSC (1953) gamut that was used for video content before it. The Ultra HD specification uses the much larger Rec. 2020 color gamut, which will allow for colors of greater saturation to be reproduced. You can see this in the image above, with sRGB being the smaller triangle, and Rec. 2020 being the larger triangle that surrounds it.

In order to support the larger Rec. 2020 color gamut without introducing color banding, a higher bit depth is required. This is because a greater number of discrete colors will be required to display gradations that span a greater range of saturations. Ultra HD Blu-ray supports 10bit per channel color depth for content that uses Rec. 2020 for its color encoding. This moves the number of possible colors that can be displayed from approximately 16.7 million to 1.07 billion. I think it would have been better to use 10bit color for sRGB content and 12bit color for Rec. 2020 content, as current 8bit sRGB content can already experience noticeable color banding, but it looks like the additional space and hardware support required have not been deemed worth it.

While the new Ultra HD Blu-ray standard supports the existing 50GB capacity for Blu-ray disks, there will be disks of greater capacity for content that requires higher bitrates. 50GB disks will have video encoded at up to 82Mbps, while 66GB disks can support up to 108Mbps, and 100GB disks support 128Mbps. In order to encode videos with these high resolutions, bitrates, and greater color depth, Ultra HD Blu-ray will make use of HEVC video encoding.

While the appeal of physical media such as Blu-ray is in decline due to the rise of streaming media, it's still the go-to for users who care about having the highest possible visual quality. It will definitely take time for Ultra HD Blu-ray to be adopted in the market, and possibly longer for Ultra HD TVs that actually support the Rec. 2020 color space. It will be interesting to see where the market for movies and TV shows moves in the future, and what position physical media will be in at that time.

Source: Blu-ray Association (via Tech Report)



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  • nathanddrews - Thursday, May 14, 2015 - link

    Audio won't improve much more than it currently has. We already have access to the lossless (and sometimes uncompressed) audio sources used in the theater. Current Blu-ray discs already come with Dolby Atmos - you just need a newer AVR that can process the flags, otherwise you just hear the "normal" 5.1/7.1 stream.

    Probably my favorite part about these new object-based audio mixes (specifically DTSX) is the ability to control object volume instead of channel volume. So if you want to increase the volume of the score and turn down everything else, you can. If you want to turn up the dialog so you can hear it over 'splosions, you can. Of course, it's unlikely that we'll be given too much freedom over that since sound engineers usually take great pride in their mixes.
  • phoenix_rizzen - Thursday, May 14, 2015 - link

    Being able to turn up the dialog and/or turn down the rest would be a welcome improvement to many movies out there. Too many times I find myself holding the remote and cranking up the audio to hear dialog, cranking down the audio during action, rinse and repeat.

    If that works well, it would be worth investing in a new audio setup.
  • Murloc - Thursday, May 14, 2015 - link

    that's because you're not doing reference listening like the technicians meant you to.
    If you want the cinema experience, you will get cinema volume dynamic range.
    You're not meant to crank it down when there are explosions.

    Anyway current AVRs can already do dynamic compression if you want to listen at low volumes, it has different names depending on the brand.
  • DanNeely - Saturday, May 16, 2015 - link

    Room shaking explosions might be fun in the cinema itself (YMMMV); but if you're trying to watch a movie at home while someone else is sleeping, or in an apartment building with poor sound proofing standard linear volume controls are inadequate. Doubly so if one of the people watching is hard of hearing and needs to turn the volume up above normal levels to hear the dialog at all. Reply
  • DanNeely - Wednesday, May 13, 2015 - link

    For anyone curious how rec 2020 compares with the Adobe RGB standard that's been common on wide gamut monitors over the last few years, Rec 2020 is about as large of an increase over it as aRBG was over sRGB.
  • Laststop311 - Wednesday, May 13, 2015 - link

    So all these early 4k adopters cant even display all the colors no rec 2020 support on current 4k tv's. I'm glad I got a 1080 lg oled instead of 4k. Need 10bit lcd screens with wide color gamut backlight or 10 bit oled that can support wide gamut before its worth buying a 4k tv. Reply
  • npz - Thursday, May 14, 2015 - link

    10-bit encoding helps prevent banding issues even on 8-bit displays. That's why you see enthusiasts use it even for things like anime, which has a lot less total colors and shades than live action, but stronger, higher contrast gradients. This is the tech white paper why:

    Unfortunately hardware manufacturers for fixed function decoders have completely ignored that. They also don't implement on the complete spec either. Current hardware support for HEVC such as in the latest Intel Broadwell CPUs don't support 10-bit profiles either, so 10-bit h.265 encodes still need to be decoded in software. I really hope that will change soon given the Ultra HD support for it.
  • Xenonite - Thursday, May 14, 2015 - link

    The above is true, however I don't mind using software decoding (I actually use it for all video decoding tasks as fixed function decoders are infamously prone to not outputting a bit-perfect decoded stream; i.e. they throw away even more data that "normal consumers with bad eyesight won't even notice" so that your desktop saves another 1 or 2 watts of power).

    I was also really excited that they would finally be implementing Rec.2020, however (as Brandon pointed out) they stupidly decided not to force 12-bit per pixel colour support (which would not really inflate video sizes that much as it just gives the HEVC encoder a bit more quantisation granularity to work with). It's also quite unbelievable that this next gen standard still defaults to 4:2:0 chroma subsampeling (which brings no benefits to modern digital video encoding and transmission; in fact, it actually further constrains the freedom that the encoder has with regards to intra-frame chroma/luma image quality optimisations).

    So the tl;dr version is basically that they had the opportunity to greatly increase both the subjective and objective video quality, while also, finally, getting rid of some ugly analog-era video encoding and transmission hacks.
    In stead, they only decided to bump up the maximum allowed bit rate a bit and to extend the saturation of colours that can be encoded without actually improving the quality with which the chroma planes get handled.
  • AnnonymousCoward - Friday, May 22, 2015 - link

    Why couldn't you be on the council? Reply
  • Rishi100 - Wednesday, May 13, 2015 - link

    It's great. I hope now, contents should be moved to 500gb usb 3 hard disk with all the additional material and appropriate copy protection for ultra HD. Reply

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