Video: State of Compression: Versatile Video Coding – H.266/VVC

An evolution from HEVC, VVC is a codec that not only delivers the traditional 50% bit rate reduction over its predecessor but also has specific optimisations for screen content (e.g. computer gaming) and 360-degree video.

Christian Feldmann from Bitmovin explains how VCC manages to deliver this bitrate reduction. Whilst VVC makes no claims to be a totally new codec, Christian explains that the fundamental way the codec works, at a basic level, is the same as all block-based codecs including MPEG 2 and AV1. The bitrate savings come from incremental improvements in technique or embracing a higher computation load to perform one function more thoroughly.

Block partitioning is one good example. Whilst AVC macroblocks are all 16×16 pixels in size, VVC allows 128×128 blocks. For larger areas of ‘solid’ colour, this allows for more efficiency. But the main advance comes in the fact you can sub-divide each of these blocks into different sized rectangles. Whilst sub-dividing has always been possible back to AVC, we have more possible shapes available now allowing the divisions to be created in closer alignment with the video.

Tiles and slices are a way of organising the macroblocks, allowing them to be treated together as a group. This is grouping isn’t taken lightly; each group can be decoded separately. This allows the video to be split into sub-videos. This can be used for multiviewer-style applications or, for instance, to allow multiple 4k decoders to decode a 16k. This could be one of those features which sees lots of innovative use…or, if it’s too complicated/restricted, will see no mainstream take-up.

Christian outlines other techniques such as intra-prediction where macroblocks are predicted from already-decoded macroblocks. Any time a codec can predict a value, this tends to reduce bitrate. Not because it necessarily gets it right, but because it then only needs an error-correction, typically a smaller number, to give it the correct value. Similarly, prediction is also possible now between the Y, U and V channels.

Finishing off, Christian hits geometric partitioning, similar to AV1, which allows diagonal splitting of macroblocks with each section having separate motion vectors. He also explains affine motion prediction, allowing blocks to scale, rotate, change aspect ration and shear. Finally Christian discusses the performance possible from the codec.

To find out more about VVC, including the content-based tuning such as for screen graphics, which is partly where the ‘versatile’ in VVC’s name comes from, listen to this talk, from 19 minutes in, given by Benjamin Bross from Fraunhofer. For Christian’s summary of all this year’s new MPEG codecs, see his previous video in the series.

Watch now!
Free to watch
Speaker

Christian Feldmann Christian Feldmann
Team Lead, Encoding
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.

Watch now!
Speakers

Christian Feldmann Christian Feldmann
Team lead, Encoding,
Bitmovin

Video: Futuristic Codecs and a Healthy Obsession with Video Startup Time

These next 12 months are going to see 3 new MPEG standards being released. What does this mean for the industry? How useful will they be and when can we start using them? MPEG’s coming to the market with a range of commercial models to show it’s learning from the mistakes of the past so it should be interesting to see the adoption levels in the year after their release. This is part of the second session of the Vienna Video Tech Meetup and delves into startup time for streaming services.

In the first talk, Dr. Christian Feldmann explains the current codec landscape highlighting the ubiquitous AVC (H.264), UHD’s friend, HEVC (H.265), and the newer VP9 & AV1. The latter two differentiate themselves by being free to used and are open, particularly AV1. Whilst slow, both the latter are seeing increasing adoption in streaming, but no one’s suggesting that AVC isn’t still the go-to codec for most online streaming.

Christian then introduces the three new codecs, EVC (Essential Video Coding), LCEVC (Low-Complexity Enhancement Video Coding) and VVC (Versatile Video Coding) all of which have different aims. We start by looking at EVC whose aim is too replicate the encoding efficiency of HEVC, but importantly to produce a royalty-free baseline profile as well as a main profile which improves efficiency further but with royalties. This will be the first time that you’ve been able to use an MPEG codec in this way to eliminate your liability for royalty payments. There is further protection in that if any of the tools is found to have patent problems, it can be individually turned off, the idea being that companies can have more confidence in deploying the new technology.

The next codec in the spotlight is LCEVC which uses an enhancement technique to encode video. The aim of this codec is to enable lower-end hardware to access high resolutions and/or lower bitrates. This can be useful in set-top boxes and for online streaming, but also for non-broadcast applications like small embedded recorders. It can achieve a light improvement in compression over HEVC, but it’s well known that HEVC is very computationally heavy.

LCEVC reduces computational needs by only encoding a lower resolution version (say, SD) of the video in a codec of your choice, whether that be AVC, HEVC or otherwise. The decoder will then decode this and upscale the video back to the original resolution, HD in this example. This would look soft, normally, but LCEVC also sends enhancement data to add back in the edges and detail that would have otherwise been lost. This can be done in CPU whilst the other decoding could be done by the dedicated AVC/HEVC hardware and naturally encoding/decoding a quarter-resolution image is much easier than the full resolution.

Lastly, VVC goes under the spotlight. This is the direct successor to HEVC and is also known as H.266. VVC naturally has the aim of improving compression over HEVC by the traditional 50% target but also has important optimisations for more types of content such as 360 degree video and screen content such as video games.

To finish this first Vienna Video Tech Meetup, Christoph Prager lays out the reasons he thinks that everyone involved in online streaming should obsess about Video Startup Time. After defining that he means the time between pressing play and seeing the first frame of video. The longer that delay, the assumption is that the longer the wait, the more users won’t bother watching. To understand what video streaming should be like, he examines Spotify’s example who have always had the goal of bringing the audio start time down to 200ms. Christophe points to this podcast for more details on what Spotify has done to optimise this metric which includes activating GUI elements before, strictly speaking, they can do anything because the audio still hasn’t loaded. This, however, has an impact of immediacy with perception being half the battle.

“for every additional second of startup delay, an additional 5.8% of your viewership leaves”

Christophe also draws on Akamai’s 2012 white paper which, among other things, investigated how startup time puts viewers off. Christophe also cites research from Snap who found that within 2 seconds, the entirety of the audience for that video would have gone. Snap, of course, to specialise in very short videos, but taken with the right caveats, this could indicate that Akamai’s numbers, if the research was repeated today, may be higher for 2020. Christophe finishes up by looking at the individual components which go towards adding latency to the user experience: Player startup time, DRM load time, Ad load time, Ad tag load time.

Watch now!
Speakers

Christian Feldmann Dr. Christian Feldmann
Team Lead Encoding,
Bitmovin
Christoph Prager Christoph Prager
Product Manager, Analytics
Bitmovin
Markus Hafellner Markus Hafellner
Product Manager, Encoding
Bitmovin

Video: Versatile Video Coding (VVC)

MPEG’s VVC is the next iteration along from HEVC (H.265). Whilst there are other codecs being finalised such as EVC and LCEVC, this talk looks at how VVC builds on HEVC, but also lends its hand to screen content and VR becoming a more versatile codec than HEVC, meeting the world’s changing needs. For an overview of these emerging codecs, this interview covers them all.

VVC is a joint project between ITU-T and MPEG (AKA ISO/IEC). Its aim is to create a 50% encoding efficiency in bitrate for the same quality picture, with the emphasis on higher resolutions, HDR and 10-bit video. At the same time, acknowledging that optimising codecs on natural video is no longer the core requirement for a lot of people. Its versatility comes from being able to encode screen content, independent sub-picture encoding, scalable encoding among others.

Gary Sullivan from Microsoft Technology & Research talks us through what all this means. He starts by outlining the case for a new codec, particularly the reach for another 50% bitrate saving which may come at further computational cost. Gary points out that video use continues to increase anything that can be done to significantly reduce bitrates, will either drive down costs or allow people to use video in better ways.

Any codec is a set of tools all working together to create the final product. Some tools are not always needed, say if you are running on a lower-power system, allowing the codec to be tuned for the situation. Gary puts up a list of some of the tools in VVC, many of which are an evolution of the same tool in HEVC, and highlights a few to give an insight into the improvements under the hood.

Gary’s pick of the big hitters in the tool-set are the Adaptive Loop Filter which reduces artefacts and prediction errors, affine motion compensation which provides better motion compensation, triangle partitioning mode which is a high-computation improvement in intra prediction, bi-directional optical flow (BIO) for motion prediction, intra-block copy which is useful for screen content where an identical block is found elsewhere in the same frame.

Gary highlights SCC, Screen Content Coding, which was in HEVC but not in the base profile, this has changed for VVC so all VVC implementations will have SCC whereas very few HEVC implementations do. Reference Picture Resampling (RPR) allows changing resolution from picture to picture where pictures can be stored at a different resolution from the current picture. And independent sub-pictures which allow parts of the video frame to be re-arranged or only for only one region to be decoded. This works well for VR, video conferencing and allows creation of composite videos without intermediate decoding.

As usual, doing more thinking about how to compress a picture brings further computational demands. MPEG’s LCEVC is the standards body’s way of fighting against this, as notable bitrate improvements are possible even for low-power devices. With VVC, versatility is the aim, however. Decoders see a 60% increase in decode complexity. Whilst MPEG specifications are all about the decoder – hence allowing a lot of ongoing innovation in encoding techniques – current examples are about 8 or 9 times slower. Performance is better for screen content and on higher resolutions. Whilst the coding part of VVC is mature, versatility is still being worked on but the aim is to publishing within about 2 months.

The video finishes with a Q&A that covers implementing in DASH into a low-latency video workflow. How CMAF will be specified to use VVC. Live workflows which Gary explains always come after the initial file-based work and is best understood after the first attempts at encoder implementations, noting that hardware lags by 2 years. He goes on to explain that chipmakers need to see the demand. At the moment, there is a lot of focus from implementors on AV1 by implementors, not to mention EVC, so the question is how much demand can be generated.

This talk is based on talk from Benjamin Bross originally given to an ITU workshop (PDF), then presented at Mile High Video by Benjamin and was updated by Gary for this conversation with the Seattle Video Tech community.

Bitmovin has an article highlighting many of the improvements in VVC written by Christian Feldmann who has given many talks on both AV1 and VVC.

Watch now!

Speakers

Gary Sullivan Gary Sullivan
Microsoft Technology & Research