Video: UHD and HDR at the BBC – Where Are We Now, and Where Are We Going? –

Has UHD been slow to roll out? Not so, we hear in this talk which explains the work to date in standardising, testing and broadcasting in UHD by the BBC and associated organisations such as the EBU.

Simon Thompson from BBC R&D points out that HD took decades to translate from an IBC demo to an on-air service, whereas UHD channels surfaced only two years after the first IBC demonstration of UHD video. UHD has had a number of updates from the initial resolution focused definition which created UHD-1, 2160p lines high and UHD-2 which is often called 8K. Later, HDR with Wide Colour Gamut (WCG) was added which allowed the image to much better replicate the brightnesses the eye is used to and almost all of the naturally-occurring colours; it turns out that HD TV (using REC.709 colour) can not reproduce many colours commonly seen at football matches.

In fact, the design brief for HDR UHD was specifically to keep images looking natural which would allow better control over the artistic effect. In terms of HDR, the aim was to have a greater range than the human eye for any one adpation state. The human eye can see an incredible range of brightnesses, but it does this by adapting to different brightness levels – for instance by changing the pupil size. When in a fixed state the eye can only access a subset of sensitivity without further adapting. The aim of HDR is to have the eye in one adaptation state due to the ambient brightness, then allow the TV to show any brightness the eye can then hold.

Simon explains the two HDR formats: Dolby’s PQ widely adopted by the film industry and the Hybrid Log-Gamma format which is usually favoured by broadcasters who show live programming. PQ, we hear from Simon, covers the whole range of the human visual system meaning that any PQ stream has the capability to describe images from 1 to 10,000 Nits. In order to make this work properly, the mix needs to know the average brightness level of the video which will not be available until the end of the recording. It also requires sending metadata and is dependent on the ambient light levels in the room.

Hybrid Log-Gamma, by contrast, works on the fly. It doesn’t attempt to send the whole range of human eye and no metadata needed. This lends itself well to delivering HDR for live productions. To learn more about the details of PQ and HLG, check out this video.

Simon outlines the extensive testing and productions done in UHD and looks at the workflows possible. The trick has been finding the best way to produce both an SDR and an HDR production at the same time. The latest version that Simon highlights had all the 70 cameras being racked in HDR by people looking at the SDR down-mix version. The aim here is to ensure that the SDR version looks perfect, as it still serves over 90% of the viewership. However, the aim is to move to a 100% HDR production with SDR being derived off the back of that without any active monitoring. The video ends with a look to the challenges yet to be overcome in UHD and HDR production.

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Simon Thompson Simon Thompson
Senior R&D Engineer

Video: A video transport protocol for content that matters

What is RIST and why’s it useful? The Reliable Internet Stream Protocol was seeing as strong uptake by broadcasters and other users wanting to use the internet to get their video from A to B over the internet even before the pandemic hit.

Kieran Kunhya from Open Broadcast Systems explains what RIST is trying to do. It comes from a history of expensive links between businesses, with fixed lines or satellite and recognises the increased use of cloud. With cloud computing increasingly forming a key part of many companies’ workflows, media needs to be sent over the internet to get into the workflow. Cloud technology, he explains, allows broadcasters to get away from the traditional on-prem model where systems need to be created to handle peak workload meaning there could be a lot of underutilised equipment.

Whilst the inclination to use the internet seems only too natural given this backdrop, RIST exists to fix the problems that the internet brings with it. It’s not controversial to say that it loses packets and adds jitter to signals. On top of that, using common file transfer technologies like HTTP on TCP leaves you susceptible to drops and variable latency. For broadcasters, it’s also important to know what your latency will be, and know it won’t change. This isn’t something that typical TCP-based technologies offer. On top of solving these problems, RIST also sets out to provide an authenticated, encrypted link.

Ways of doing this have been done before, with Zixi and VideoFlow being two examples that Kieran cites. RIST was created in order to allow interoperability between equipment in a vendor-neutral way. To underline it’s open nature, Kieran shows a table of the IETF RFCs used as part of the protocol.

RIST has two groups of features, those in the ‘Simple Profile’ such as use of RTP, packet loss recovery, bonding and hitless switching. Whereas the ‘Main Profile’ adds on top of that tunnelling (including the ability to choose which direction you set up your connection), encryption, authentication and null packets removal. Both of these are available as published specifications today. A third group of features is being planned under the ‘enhanced profile’ to be released around the beginning of Q2 2021.

Kieran discusses real-world proof points such as a 10-month link which had lost zero packets, though had needed to correct for millions of lost packets. He discusses deployments and moves on to SRT. SRT, Secure Reliable Transport, is a very popular technology which achieves a lot of what RIST does. Although it is an open-source project, it is controlled by one vendor, Haivision. It’s easy to use and has seen very wide deployment and it has done much to educate the market so people understand why they need a protocol such as RIST and SRT so has left a thirst in the market. Kieran sees benefit in RIST having brought together a whole range of industry experts, including Haivision, to develop this protocol and that it already has multipath support, unlike SRT. Furthermore, at 15% packet loss, SRT doesn’t work effectively whereas RIST can achieve full effectiveness with 40% packet loss, as long as you have enough bandwidth for a 200% overhead.

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Kieran Kunhya Kieran Kunhya
Director, RIST Forum
Founder & CEO, Open Broadcast Systems

Video: Let’s be hAV1ng you

AV1 is now in use for some YouTube feeds, Netflix also can deliver AV1 to Android devices so we are no longer talking about “if AV1 happens” or “when AV1’s finished”. AV1 is here to stay, but in a landscape of 3 new MPEG codecs, VVC, EVC and LCEVC, the question moves to “when is AV1 the right move?”

In this talk from Derek Buitenhuis, we delve behind the scenes of AV1 to see which AV1 terms can be, more-or-less, mapped to which MPEG terms. AV1 is promoted as a royalty-free codec, although notably a patent pool has appeared to try and claim money from users. Because it’s not reusing ideas from other technologies, the names and specific functions of parts of the spec are both not identical to other codecs, but are similar in function.

Derek starts by outlining some of the terms we need to understand before delving in further such as “Temporal Unit” which of course is called a TU and is analogous to a GOP. Then he moves on to highlight the many ways in which previous DCT-style work has been extended meaning the sizes and types of DCT have been increased, and the prediction modes have changed. All of this is possible but increases computation.

Derek then highlights several major tools which have been added. One is the prediction of the Chroma from the Luma signal. Another is the ‘Constrained Direction Enhancement Filter’ which improves the look of diagonal hard edges. The third is ‘switch frames’ which are similar to IDR frames or, as Derek puts it ‘a fancy P-frame.’ There is also a Multi-Symbolic Arithmetic Codec which is a method of guessing a future binary digit which, based on probability, allows you to encode a subset of the number but just enough to ensure that the algorithm will come out with the full number,

After talking about the Loop Restoration Filter Derek then critiques a BBC article which drew, it seems, incorrect conclusions based on not enabling the appropriate functions needed for good compression and also suggesting that there was not enough information provided for anyone else to replicate the experiment. Derek then finishes with MS-SIM plots of different encoders.

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Download the slides.

Derek Buitenhuis Derek Buitenhuis
Senior Video Encoding Engineer,

Video: A Forensic Approach to Video

Unplayable media is everyone’s nightmare, made all the worse if it could be key evidence in a crimnial case. This is daily fight that Gareth Harbord from the Metropolitan Police has as he tries to render old CCTV footage and files from crashed dash cams playable, files from damaged SD cards and hard drives readable and recover video from old tape formats which have been obselete for years.

In terms of data recovery, there are two main elments: Getting the data off the device and then fixing the data to make it playable. Getting the data off a device tends to be difficult because either the device is damaged and/or connecting to the device requires some proprietary hardware/software which simply isn’t available any more. Pioneers in a field often have to come up with their own way of interfacing which, when the market becomes bigger, is often then improved by a standard way of doing things. Take, as an example, mobile phone cables. They used to be all sorts of shapes and sizes but are now much more uniform with 3 main types. The same was initially true with hard drives, however the first hard drives were so long ago that osolecence is much more of an issue.

Once you have the data on your own system, it’s then time to start analysing it to see why it won’t play. It may play because the data itself is of an old or proprietary format, which Gareth says is very common with CCTV manufacturers. While there are some poular formats, there are many variations from different companies including putting all, say, 4 cameras onto one image or into one file, running the data for the four cameras in parallel. After a while, you start to be able to get a feel for the formats but not without many hours of previous trial and error.

Gareth starts his talk explaining that he works in the download and data receovery function which is different from the people who make the evidence ready for presentation in a trial. Their job is to find the best way to show the relevant parts both in terms of presentation but also technically making sure it is easy to play for the technically uninitiated in court and that it is robust and reliable. Presentation covers the effort behind combining multiple sources of video evidence into one timeline and ensuring the correct chronology. Other teams also deal with enhancing the video and Gareth shows examples of deblurring an image and also using frame averaging to enhance the intelligability of the picture.

Gareth spends some time discussing CCTV where he calls the result of the lack of standardisation “a myriad of madness.” He says it’s not uncommon to have 15-year-old systems which are brought in but, since the hard drives have been spinning for one and half decades, don’t start again when they are repowered. On the otherhand the newer IP cameras are more complicated whereby each camera is generating its own time-stampped video going into a networked video recorder which also has a timestamp. What happens when all of the timestamps disagree?

Mobile devices cause problems due to variable frame rates which are used to deal with dim scenes, non-conformance with standards and who can forget the fun of CMOS videos where the CMOS sensors lead to wobbling of the image when the phone is panned left or right. Gareth highlights a few of the tools he and his colleagues use such as the ever-informative MediaInfo and FFProbe before discussing the formats that they transode to in order to share the videos internally.

Gareth walks us through an example file looking at the how data can be lined up to start understanding the structure and start to decode it. This can lead to the need to write some simple code in C#, or similar, to rework the data. When it’s not possible to get hold of the data in a partiular format to be playable in VLC, or similar, a proprietary player may be the only way forward. When this is the case, often a capture of the computer screen is the only way to excerpt the clip. Gareth looks at the pros and cons of this method.

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Gareth Harbord Gareth Harbord
Senior Digital Forensic Specialist (Video)
Metropolitan Police Service