Video: The New Video Codec Landscape – VVC, EVC, HEVC, LC-EVC, AV1 and more

The codec arena is a lot more complex than before. Gone is the world of 5 years ago with AVC doing nearly everything. Whilst AVC is still a major force, we now have AV1 and VP9 being used globally with billions of uses a year, HEVC is not the force majeure it was once expected to be, but is now seeing significant use on iPhones and overall adoption continues to grow. And now, in 2020 we see three new codecs on the scene, VVC, EVC and LCEVC.

To help us make sense of this SMPTE has invited Walt Husak and Sean McCarthy to take us through what the current codecs are, what makes them different, how well they work, how to compare them and what the future roadmaps hold.

Sean starts by explaining which codecs are maintained by which bodies, with the IEC, ITU and MPEG being involved, not to mention the corporate codecs (VP8, and VP9 from Google) and the Chinese AVS series of codecs. Sean explains that these share major common elements and are each evolutions of each other. But why are all these codecs needed? Next, we see the use-cases that have brought these codecs into existence. Granted, AVC and HEVC entered the scene to reduce bit rate in an effort to make HD and UHD practical, respectively, but EVC and LC-EVC have different aims.

Sean gives a brief overview of the basics of encoding starting with partitioning the image, predicting parts of it, applying transformations, refining it (also known as applying ‘loop filters) and finishing with entropy codings. All of these blocks are briefly explained and exist in all the codecs covered in this talk. The evolutions which make the newer codecs better are therefore evolutions of each of these elements. For instance, explains Sean, splitting the image into different sections, known as partitioning, has become more sophisticated in recent codecs allowing for larger sections to be considered at once but, at the same time, smaller partitions created within each.

All codecs have profiles whereby the tools in use, or the complexity of their implementation, is standardised for certain types of video: 8-bit, 10-bit, HDR etc. This allows hardware implementers to understand the upper bounds of computation so they don’t end up over-provisioning hardware resources and increasing the cost. Sean looks at how VVC uses the same tools throughout all of its four profiles with only a few exceptions. Screen content sees two extra tools come for 4:2:2 formats and above. AV1 has the same tools throughout all the profiles but, deliberately, EVC doesn’t. Essential Video Coding has a royalty-free base layer which uses techniques that are not subject to any use payments. Using this layer gives you AVC-quality encoding, approximately. Using the main profile, however, gets you similar to HEVC encoding albeit with royalty payments.

The next part of the talk examines two main reasons for the increase in compression over recent codec generation, block size and partitioning, before highlighting some new tools in VVC and AV1. Block size refers to the size of the blocks that an image is split up into for processing. By using a larger block, the algorithms can spot patterns more efficiently so the continued increase from 16×16 in AVC to 128×128 now in VVC drives an increase in computation but also in compression. Once you have your block, splitting it up following the features of the images is the next stage. Called partitioning, we see the number of ways that the codecs can mathematically split a block has grown significantly. VVC can also partition chroma separately to luma. VVC and AV1 also include 64 and 16 ways, respectively, to diagonally partition rather than the typical vertical and horizontal partitioning modes.

Screen content coding tools are increasingly important, pandemics aside, there has long been growth in the amount of computer-generated content being shared online whether that’s through esports, video conference screen sharing or elsewhere. Truth be told, HEVC has support for screen-content encoding but it’s not in the main profile so many implementations don’t support it. VVC not only evolves the screen-content tools, but it also makes it present as default. AV1, also, was designed to work well with screen content. Sean takes some time to look at the IBC tool, intra-block copy, which allows the encoder to relate parts of the current frame to other sections. Working at the prediction stage, with screen content which contains, for instance, lots of text, parts of that text will look similar and to a first approximation, one part of the image can be duplicated in another. This is similar to motion compensation where a macroblock is ‘copied’ to another frame in a different position, but all the work is done on the present frame for Intra BC. Palette mode is another screen content tool which allows the colour of a section of the image to be described as a palette of colours rather than using the full RGB value for each and every pixel.

Sean covers the scaled prediction between resolutions in VVC and super-resolution in AV1, VVC’s 360-degree video optimisations and luma mapping before handing over to Walt Husak who goes into more detail on how the newer codecs work, starting with LCEVC.

LCEVC is a codec which improves the performance of already-deployed codecs, typically used to enhance the spatial resolution. If you wanted to encode HD, the codec would downsample the HD to an SD resolution and encode that with AVC, HEVC or another codec. At the same time, it would upsample that encoded video again and generate to correction layers which correct for artefacts and add sharpness. This information is added into to the base codec and sent to the decoder. This can allow a software-only enhancement to a hardware deployment fully utilising the hardware which has already been deployed. Walt notes that the enhancement layers are much the same technology as has already been standardised by SMPTE as VC6 (ST 2117). LCEVC has been found to be computationally efficient allowing it to address markets such as embedded devices where hardware restrictions would otherwise prohibit use of higher resolutions than for which it was originally designed. Very low bitrate performance is also very good.

Sean introduces us to his “Dos and Don’ts” of codec comparisons. The theme running through them is to take care that you are comparing like for like. Codecs can be set to run ‘fast’ or ‘slow’ each of which holds its own compromises in terms of encoding time and resulting quality. Similarly, there are some implementations which are made simply to implement the standard as rigorously as possible which is an invaluable tool when developing the codec or an implementation. Such a reference implementation for codec X, clearly, shouldn’t be compared to production implementations of a codec Y as the times are guaranteed to be very different and you will not learn anything from the process. Similarly, there are different tools which give codecs much more time to optimise known as single- and double-pass which shouldn’t be cross-compared.

The talk draws to a close with a look at codec performance. Sean shows a number of graphs showing how VVC performs against HEVC. Interestingly the metrics clearly show a 40% increase in efficiency of VVC over HEVC, but when seen in subjective tests, the ratings show a 50% improvement. VVC’s encoder is approximately 10x as complex as HEVC’s.

HEVC and AV1 perform similarly for the same bit rate. Overall, Sean says, AV1 is a little blurrier in regions of spatial detail and can have some temporal flickering. HEVC is more likely to have blocking and ringing artefacts. EVC’s main profile is up to 29% better than HEVC. LCEVC performs up to 8% better than AVC when using an AVC base layer and also slightly better than HEVC when using an HEVC base codec. Sean makes the point that the AVC has been continually updated since its initial release and is now on version 27, so it’s not strictly true to simply say it’s an ‘old’ codec. HEVC similarly is on version 7. Sean runs down part of the roadmap for AVC which leads on to the use of AI in codecs.

Finishing the video, Walt looks at the use of Deep Learning in codecs. Deep learning is also known as machine learning and referred to as AI (Artificial Intelligence). For most people, these terms are interchangeable and refer to the ability of a signal to be manipulated not by a fixed equation or algorithm (such as Lanczos scaling) but by a computer that has been trained through many millions of examples to recognise what looks ‘right’ and to replicate that effect in new scenarios.

Walt talks about JPEG’s AI learning research on still images who are aiming to complete an ‘end-to-end’ study of compression with AI tools. There’s also MPEG’s Deep Neural Network-based Video Coding which is looking at which tools within codecs can be replaced with AI. Also, recently we have seen the foundation of the MPAI (Moving Picture, Audio and Data Coding by Artificial Intelligence) organisation by Leonardo Chiariglione, an industry body devoted to the use of AI in compression. With all this activity, it’s clear that future advances in compression will be driven by the increasing use of these techniques.

The video ends with a Q&A session.

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Find out more on SMPTE’s site
Speakers

Sean McCarthy Sean McCarthy
Director, Video Strategy and Standards,
Dolby Laboratories
Walt Husak Walt Husak
Director, Image Technologies,
Dolby Laboratories

Video: Line by Line Processing of Video on IT Hardware

If the tyranny of frame buffers is let to continue, line-latency I/O is rendered impossible without increasing frame-rate to 60fps or, preferably, beyond. In SDI, hardware was able to process video line-by-line. Now, with uncompressed SDI, is the same possible with IT hardware?

Kieran Kunhya from Open Broadcast Systems explains how he has been able to develop line-latency video I/O with SMPTE 2110, how he’s coupled that with low-latency AVC and HEVC encoding and the challenges his company has had to overcome.

The commercial drivers are fairly well known for reducing the latency. Firstly, for standard 1080i50, typically treated as 25fps, if you have a single frame buffer, you are treated to a 40ms delay. If you need multiple buffers for a workflow, this soon stacks up so whatever the latency of your codec – uncompressed or JPEG XS, for example – the latency will be far above it. In today’s covid world, companies are looking for cutting the latency so people can work remotely. This has only intensified the interest that was already there for the purposes of remote production (REMIs) in having low-latency feeds. In the Covid world, low latency allows full engagement in conversations which is vital for news anchors to conduct interviews as well as they would in person.

IP, itself, has come into its own during recent times where there has been no-one around to move an SDI cable, being able to log in and scale up, or down, SMPTE ST 2110 infrastructure remotely is a major benefit. IT equipment has been shown to be fairly resilient to supply chain disruption during the pandemic, says Kieran, due to the industry being larger and being used to scaling up.

Kieran’s approach to receiving ST 2110 deals in chunks of 5 to 10 lines. This gives you time to process the last few lines whilst you are waiting for the next to arrive. This processing can be de-encapsulation, processing the pixel values to translate to another format or to modify the values to key on graphics.

As the world is focussed on delivering in and out of unusual and residential places, low-bitrate is the name of the game. So Kieran looks at low-latency HEVC/AVC encoding as part of an example workflow which takes in ST 2110 video at the broadcaster and encodes to MPEG to deliver to the home. In the home, the video is likely to be decoded natively on a computer, but Kieran shows an SDI card which can be used to deliver in traditional baseband if necessary.

Kieran talks about the dos and don’ts of encoding and decoding with AVC and HEVC with low latency targetting an end-to-end budget of 100ms. The name of the game is to avoid waiting for whole frames, so refreshing the screen with I-frame information in small slices, is one way of keeping the decoder supplied with fresh information without having to take the full-frame hit of 40ms (for 1080i50). Audio is best sent uncompressed to ensure its latency is lower than that of the video.

Decoding requires carefully handling the slice boundaries, ensuring deblocking i used so there are no artefacts seen. Compressed video is often not PTP locked which does mean that delivery into most ST 2110 infrastructures requires frame synchronising and resampling audio.

Kieran foresees increasing use of 2110 to MPEG Transport Stream back to 2110 workflows during the pandemic and finishes by discussing the tradeoffs in delivering during Covid.

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Speaker

Kieran Kunhya Kieran Kunhya
CEO & Founder, Open Broadcast Systems

Video: The Video Codec Landscape 2020

2020 has brought a bevy of new codecs from MPEG. These codecs represent a new recognition that the right codec is the one which fits your hardware and your business case. We have the natural evolution of HEVC, namely VVC which trades on complexity to achieve impressive bit rate savings. There’s a recognition that sometimes a better codec is one that has lower computation, namely LCEVC which enables a step-change in quality for lower-power equipment. And there’s also EVC which has a license-free mode to reduce the risk for companies which prefer low-risk deployments.

Christian Feldmann from Bitmovin takes the stage in this video to introduce these three new contenders in an increasingly busy codec landscape. Christian starts by talking about the incumbents namely AVC, HEVC, VP9 and AV1. He puts their propositions up against the promises of these new codecs which are all at the point of finalisation/publication. With the current codecs, Christian looks at what the hardware and software support is like as well as the licencing.

EVC (Essential Video Codec) is the first focus of the presentation whose headline feature is more reliably licence landscape. The first offer is the baseline profile which has no licencing as it uses technologies which are old enough to be outside of patents. The main profile does require licencing and does allow much better performance. Furthermore, the advanced tools in the main profile can each be turned off individually hence avoiding patents that you don’t want to licence. The hope is that this will encourage the patent holders to licence the technology in a timely manner else the customer can, relatively easily, walk away. Using the baseline only should provide 32% better than AVC and the main profile can give up to a 25% benefit over HEVC.

LCEVC (Low Complexity Enhancement Video Coding) is next which is a new technique for encoding which is actually two codecs working together. It uses a ‘base’ codec at low resolution like AVC, HEVC, AV1 etc. This low fidelity version is then accompanied by enhancement information so that the low-resolution base can be upscaled to the desired resolution can be corrected with relevant edges etc. added. The overall effect is that complexity is kept low. It’s designed as a software codec which can fit into almost any hardware by using the hardware decoders in SoCs/CPUs (i.e. Intel QuickSync) plus the CPU itself which deals with the enhancement application. This ability to fit around hardware makes the codec ideal for improving the decoding capability to existing hardware. It stands up well against AVC providing at least 36% improvement and at worst improves slightly upon HEVC bitrates but with much-reduced encoder computation.

VVC (Versatile Video Coding) is discussed by Christian but not in great detail as Bitmovin will be covering that separately. As an evolution of HEVC, it’s no surprise that bitrate is reduced by at least 40%, though encoding complexity has gone up 10-fold. This is similar to HEVC compared to its predecessor AVC. VVC has some built-in features not delivered as standard before such as special modes for screen content (such as computer games) and 360-degree video.

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Speaker

Christian Feldmann Christian Feldmann
Lead encoding engineer,
Bitmovin

Video: Outlook on the future codec landscape

VVC has now been released, MPEG’s successor to HEVC. But what is it? And whilst it brings 50% bitrate savings over HEVC, how does it compare to other codecs like AV1 and the other new MPEG standards? This primer answers these questions and more.

Christian Feldmann from Bitmovin starts by looking at four of the current codecs, AVC, HEVC, VP9 and AV1. VP9 isn’t often heard about in traditional broadcast circles, but it’s relatively well used online as it’s supported on Android phones and brings bitrate savings over AVC. Google use VP9 on Youtube for compatible players and see a higher retention rate. Netflix and Twitch also use it. AV1 is also in use by the tech giants, though its use outside of those who built it (Netflix, Facebook etc.) is not yet apparent. Christian looks at the compatibility of the codecs, hardware decoding, efficiency and cost.

Looking now at the other upcoming MPEG codecs, Christian examines MPEG-5 Essential Video Coding (EVC) which has two profiles: Baseline and Main. The baseline profile only uses technologies which are old enough to be outside of patent claims. This allows you to use the codec without the concern that you may be asked for a fee from a patent holder who comes out of the woodwork. The main profile, however, does have patented technology and performs better. Businesses which wish to use this codec can then pay licences but if an unexpected patent holder appears, each individual tool in the codec can be disabled, allowing you to protect continue using, albeit without that technology. Whilst it is a shame that patents are so difficult to account for, this shows MPEG has taken seriously the situation with HEVC which famously has hundreds of licensable patents with over a third of eligible companies not part of a patent pool. EVC performs 32% better than AVC using the baseline profile and 25% better than HEVC with the main profile.

Next under the magnifying glass is Low Complexity Enhancement Video Coding (LCEVC). We’ve already heard about this on The Broadcast Knowledge from Guido, CEO of V-Nova who gave a deeper look at Demuxed 2019 and more recently at Streaming Media West. Whilst those are detailed talks, this is a great overview of the technology which is actually a hybrid approach to encoding. It allows you to take any existing codec such as AVC, AV1 etc. and put LCEVC on top of it. Using both together allows you to run your base encoder at a lower resolution (say HD instead of UHD) and then deliver to the decoder this low-resolution encode plus a small stream of enhancement information which the decoder uses to bring the video back up to size and add back in the missing detail. The big win here, as the name indicates, is that this method is very flexible and can take advantage of all sorts of available computing power in embedded technology as and in servers. In set-top boxes, parts of the SoC which aren’t used can be put to use. In phones, both the onboard HEVC decoding chip and the CPU can be used. It’s also useful in for automated workflows as the base codec stream is smaller and hence easier to decode, plus the enhancement information concentrates on the edges of objects so can be used on its own by AI/machine learning algorithms to more readily analyse video footage. Encoding time drops by over a third for AVC and EVC.

Now, Christian looks at the codec-du-jour, Versatile Video Codec (VVC), explaining that its enhancements over HEVC come not just from bitrate improvements but techniques which better encode screen content (i.e. computer games), allow for better 360 degree video and reduce delay. Subjective results show up to 50% improvement. For more detail on VVC, check out this talk from Microsoft’s Gary Sullivan.

The talk finishes with answers so audience questions: Which will be the winner, what future device & hardware support will be and which is best for real-time streaming.

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Speakers

Christian Feldmann Christian Feldmann
Team lead, Encoding,
Bitmovin