WCG Archives – The Broadcast Knowledge

Video: Video Fundamentals in Depth

Posted on 23rd April 2021 by Russell Trafford-Jones

Whether you feel your productivity has gone up down during Covid lockdowns, most people seem to be busier than ever making it all the harder to get the depth of knowledge needed to change from knowing how to get things done to know why it works and being able to adapt to new demands. However you work with video, whether in the edit suite, in a transmission MCR or otherwise, knowing how video is processed, represented and stored is really valuable and can speed up your work and faultfinding.

Noah Chamow from the Assistant Editor’s Bootcamp, is here with a true video fundamentals course. In four sections, this three-hour course takes you through how images are structured, compressed, stored and looks at colour. The first portion is a look at resolution, aspect ratio (including cameras, lenses and delivery aspect ratios), interlaced images, frame rates and timecode.

The codecs section explains the basics of compression and then moves on to post-production codecs such as ProRes, DNxHD etc. before moving on to looking at the bitrates contained within. Colour is a big topic which Noah introduces with standard 2D and 3D colour charts building up to the idea of colour depth such as 8 bit, 10 bit etc. If you’re interested in more detail on colour spaces and fundamentals, this SMPTE deep dive should deliver the goods. Noah moves on to HDR next, talking about both the extended luminance brightness as well as the Wide Colour Gamut aspects such as BT.2020 which all links back to his previous section about on image bit depth.

For a deeper dive into codecs, check out this SMPTE video and for a closer look at HDR, Tektronix’s Steve Holmes does so in this video.

Important in the post-production side of the industry is understanding formats like Blackmagic RAW and ARRIRAW which are discussed. They are large files that can push computers to the extremes and need processing such as debayering. Chroma sampling is an important concept as all of the video getting to viewers has had colour information removed. If you’re interested in editing, you need to understand this so you know which files will give you the best output. If you’re in contribution or transmission, it’s important to know the difference between video coming to you with either 4:2:2 or 4:2:0. Noah explains what all this means and why we do this in the first place.

The video concludes by looking at video containers. Noah starts by talking about the Mov, also known as ‘Quicktime’, container. If you have and ‘off-beat’ sense of humour you may enjoy this video on containers and codecs from Adult Swim. With a lot more decorum, Noah covers MXF and moving between container formats in your editing software.

Whether you’ve been asking “Which codec should I use?”, struggling to understand steps in your workflow or just trying to find ways to get your work done better for faster, this training session should help deepen your understanding of video giving you the context that you need.

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Speaker

Noah Chamow
Co-Founder, Assistant Editors’ Bootcamp
Assistant Online Editor, Level 3 Post

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

Posted on 16th December 2020 by Russell Trafford-Jones

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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Speaker

Simon Thompson
Senior R&D Engineer
BBC R&D

Video: 5 Myths About Dolby Vision & HDR debunked

Posted on 10th September 2020 by Russell Trafford-Jones

There seem no let up in the number of technologies coming to market and whilst some, like HDR, have been slowly advancing on us for many years, the technologies that enable them such as Dolby Vision, HDR10+ and the metadata handling technologies further upstream are more recent. So it’s no surprise that there is some confusion over what’s possible and what’s not.

In this video, Bitmovin and Dolby the truth behind 5 myths surrounding the implementation and financial impact of Dolby Vision and HDR in general. Bitmovin sets the scene by with Sean McCarthy giving an overview on their research into the market. He explains why quality remains important, simply put to either keep up with competitors or be a differentiator. Sean then gives an overview of the ‘better pixels’ principle underlining that improving the pixels themselves is often more effective than higher resolution, technologies such as wide colour gamut (WCG) and HDR.

David Brooks then explains why HDR looks better, explaining the biology and psychology behind the effect as well as the technology itself. The trick with HDR is that there are no extra brightness values for the pixels, rather the brightness of each pixel is mapped onto a larger range. It’s this mapping which is the strength of the technology, altering the mapping gives different results, ultimately allowing you to run SDR and HDR workflows in parallel. David explains how HDR can be mapped down to low-brightness displays,

The last half of this video is dedicated to the myths. Each myth has several slides of explanation, for instance, the one suggests that the workflows are very complex. Hangen Last walks through a number of scenarios showing how dual (or even three-way) workflows can be achieved. The other myths, and the questions at the end, talk about resolution, licensing cost, metadata, managing dual SDR/HDR assets and live workflows with Dolby Vision.

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Speakers

	David Brooks Senior Director, Professional Solutions, Dolby Laboratories
	Hagan Last Technology Manager, Content Distribution, Dolby Laboratories
	Sean McCarthy Senior Technical Product Marketing Manager, Bitmovin
	Moderator: Kieran Farr VP Marketing, Bitmovin

Video: Extension to 4K resolution of a Parametric Model for Perceptual Video Quality

Posted on 26th February 2020 by Russell Trafford-Jones

Measuring video quality automatically is invaluable and, for many uses, essential. But as video evolves with higher frame rates, HDR, a wider colour gamut (WCG) and higher resolutions, we need to make sure the automatic evaluations evolve too. Called ‘Objective Metrics’, these computer-based assessments go by the name of PSNR, DMOS, VMAF and others. One use for these metrics is to automatically analyse an encoded video to determine if it looks good enough and should be re-encoded. This allows for the bitrate to be optimised for quality. Rafael Sotelo, from the Universidad de Montevideo, explains how his university helped work on an update to Predicted MOS to do just this.

MOS is the Mean Opinion Score and is a result derived from a group of people watching some content in a controlled environment. They vote to say how they feel about the content and the data, when combined gives an indication of the quality of the video. The trick is to enable a computer to predict what people will say. Rafael explains how this is done looking at some of the maths behind the predicted score.

In order to test any ‘upgrades’ to the objective metric, you need to test it against people’s actual score. So Rafael explains how he set up his viewing environments in both Uruguay and Italy to be compliant with BT.500. BT.500 is a standard which explains how a room should be in order to have viewing conditions which maximise the ability of the viewers to appreciate the pros and cons of the content. For instance, it explains how dim the room should be, how reflective the screens and how they should be calibrated. The guidelines don’t apply to HDR, 4K etc. so the team devised an extension to the standard in order to carryout the testing. This is called ‘subjective testing’.

With all of this work done, Rafael shows us the benefits of using this extended metric and the results achieved.

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Speakers