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Why low complexity video encoding is the answer to the success of UHD television


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Since the start of regular BBC television broadcasting from my hometown of London on the 26the August 1936, the broadcasting industry and the technology ecosystem around it are continually striving to improve and make it more beautiful. However, in recent years, we have failed to upgrade traditional terrestrial broadcasting to ultra-high definition (UHD), with the result that most people who have bought UHD TVs have never watched. of real UHD TV content on it!

Rick clucas

The main reason that UHD TVs have been such a big hit for TV manufacturers is that they have the ability to sell premium products that, for the same screen size, actually cost them. less to manufacture as a Full HD panel. This is because the display output yield for UHD is higher than for Full HD, because there are four times as many pixels for the same screen size, which means that the allowed percentage of non-pixel pixels. defective is much easier to reach.

Unfortunately, from 2021 onwards, UHD remained impractical for broadcasters, as current video codecs consume too much valuable spectrum. In particular, it does not make economic sense to broadcast in UHD, because

  • the bandwidth requirements of UHD channels are too high, and
  • Moreover, they should always stream a Full HD version separately for the large number of viewers who do not have UHD TVs.

Another dimension is that the lack of UHD content has made it easier to enter the market for new OTT services with higher quality content, putting additional pressure on the revenue streams of traditional broadcasters.

Modern digital video codecs have been designed around single-channel transmission. The industry developed High Efficiency Video Coding (HEVC) in 2012 to reduce bandwidth requirements, but HEVC could only be used to transmit services intended for new devices, as existing receiving devices would not be in service. able to decode them.

If we look at the history of television, we once faced a similar challenge with the introduction of color television into the analog world, where spectrum was even more scarce than it is in our world of. current digital transmission. It would have been impractical to broadcast new color channels incompatible with traditional receivers, as there would not have been enough spectrum to broadcast them with the existing black and white channels.

As an industry, we came up with a few tools to solve this problem: one was to downsample color information, and the other – what I would call the “great” solution – was that we didn’t ‘planes to send the additional information required for color (Chroma) with a backward compatible black and white (Luma) channel. This meant that all viewers with old receivers could continue to watch black-and-white channels, while customers with newer TVs could watch color TV instead.

In 2018, MPEG recognized that in addition to working on whole new codecs, which require the creation and deployment of new ecosystems before being used, it made sense to have a low complexity enhancement codec that could be applied to any existing or future codec. to allow the delivery of a conventional video stream to everyone (similar to the old black and white) with a small amount of additional enhancement data allowing improved image quality at higher resolution for people who have receivers compatible with the new enhancement codec.

The above approach is made even more impactful by the fact that:

  • the overall bandwidth requirement of an enhanced channel (that is, the “base” stream plus enhancement data) is lower than that of a full resolution channel encoded with the codec of base used alone, and
  • many existing receivers can be retrofitted via software to be compatible with the enhancement codec.

One approach proposed as a starting point to meet this requirement used V-Nova technology. As a result, after hard work by many industry organizations, the ISO / IEC 23094-2 Low Complexity Enhancement Video Codec MPEG-5 Part 2 (LCEVC) standard has finally been completed.

LCEVC-encoder-decode-block block diagram
LCEVC is an enrichment codec, that is to say that it is not satisfied with well oversampling: it will also encode the residual information necessary for a true fidelity to the source and compress it (transform it, quantify it and encode it). LCEVC can also produce mathematically lossless reconstructions, which means that all information can be encoded and transmitted and the image perfectly reconstructed. Creator’s intent, small text, logos, advertisements and unpredictable details in high resolution are preserved with LCEVC. (Source: V-Nova)

The LCEVC also brings an interesting “psychological” challenge to an industry accustomed to manufacturing and selling new equipment to each new standard. LCEVC is “low complexity”, which means that while it can be implemented in hardware (and probably will be in the future), it can also do what no other video codec has done before: be implemented using existing hardware blocks through a new device driver. In addition, these same blocks that we use to implement in current generation chips also exist in older chips, providing the unique opportunity to modernize the LCEVC on a large number of existing TVs and set-top boxes (STBs) via an upgrade. up to date live. , allowing UHD television to reach terrestrial television today, without having to wait until everyone has bought new equipment.

With LCEVC, a UHD channel would have 1080p “base” video – so any device that is not LCEVC compliant would still get 1080p video. LCEVC data typically adds 10-20% to lower resolution base video, so the new combined channel (base and enhancement data) is significantly smaller than a full resolution channel broadcast without LCEVC. Most importantly, for streaming services, you don’t need to stream two channels at the same time.

I think – somewhat paradoxically – being retrofitable on many existing devices and backward compatible on the rest will lead to increased sales of new UHD equipment, thanks to greater availability of high-quality UHD content. By making the delivery of UHD content commercially viable for terrestrial television, LCEVC achieves what any new codec may find impossible to achieve: that is, reducing the bit rate enough that broadcasters can afford to send all new UHD channels on top of their full legacy. those in HD.

Finally, one of the great advantages of LCEVC is that it is not offered as an alternative to future codecs at all, as it improves them as well: using VVC or AV1 with LCEVC produces better quality than using of VVC (versatile video encoding) or AV1 (AOM video 1) video encoding schemes by themselves and save a lot of energy for encoding and decoding. In fact, combining LCEVC with AV1 has already been shown to reduce transcoding processing requirements by up to 70% and even make AV1 delivery to mobile devices more viable, due to the fact that enhanced AV1 LCEVC can run on many more devices and extends battery life by up to 50% compared to using AV1 alone.

Rick Clucas is SVP Innovation and Technology at V-Nova.


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