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Live Streaming at Sky: Streaming Forum Keynote Preview
Sky's prinicipal streaming architect Jeff Webb will keynote Streaming Forum 2018 in London. In the first article in a five-part series, he takes a look at the transcoding challenges involved in delivering live sports and entertainment OTT content to Sky's viewers.

This is the first in a series of five articles previewing the keynote at February's Streaming Forum. See the links at the end of ths article for the rest of the series.

What does it really mean to operate a live streaming platform at scale for millions of customers every day? As one of Europe's leading pay TV operators, our customers know that when it has Sky's name on it, they can expect to receive a premium streaming experience with the best sports, entertainment and movie content.

As we get closer to my keynote at Streaming Forum in London in February, I wanted to give a bit of background and insight into Sky's live streaming services. My goal with this series of five articles is not to explain how we do it, but to address the far more important question of why we make the decisions we do to deliver on our promise. I'll delve further into how we do it during the keynote.

By the end of this series of five articles, you will have a good understanding of the five key areas that make up Sky's live streaming platform: transcoding, packaging, encryption, origin/CDNs and quality of experience.


It's 2 p.m. on a Sunday afternoon at a Premier League football stadium in West London. The stadium comes to life with the noise of the crowd and the colours of the two teams. The TV cameras are carefully placed to capture the action as we kick off and send live pictures to the outside broadcast truck and onto Sky Studios. For Sky customers streaming content to their NOW TV box or mobile phone, they are blissfully unaware of the technical challenges that go into making this a reality.

Within economics, there is the oft-quoted maxim of "doing more with less" and making efficient use of available resources. So how does this relate to streaming, and how do we make this magic come alive and ensure customers enjoy a good experience? 

If we start with the end in mind, then from a customer's perspective video compression is critical to the success of the streaming experience regardless of device and screen size. For example, sports and news have very different transcoding challenges, which can be observed when comparing sports' fast motion complexity with the camera pans among talking heads in a studio.

Within the industry, there's a growing trend to switch from SDI to IP contribution feeds as this provides additional flexibility at a lower cost. Using a mezzanine IP feed as your high-quality video source for the transcoder provides consistency and leverages the existing networks ability to route content to where it is needed. Transcoding is one of the most computationally expensive operations, requiring significant CPU/GPU performance to achieve reasonable channel density.

In the modern live channel workflow, being able to consistently stand up channels within minutes through automation is highly desirable and removes the need for specialised hardware. Whilst modern servers are designed for general-purpose computing, transcoding multiple bitrates benefits from having as many cores as possible, although there may be an upper limit. One exciting concept borrowed from the web world is containerisation, where applications can be used to rightsize workloads across your server estate.

Choosing an effective adaptive bitrate (ABR) ladder is a key decision that needs to be balanced against the client devices' ability to consume internet content without buffering. We can make a reasonable assumption that most non-mobile devices are connected through a Wi-Fi or wired connection and will tend to consume higher bitrates. By comparison, mobile devices are typically used for live sporting events, when a higher bandwidth connection is not available.

As a broadcaster, we want all our customers to receive the best picture quality, and we take a data-driven approach, using automated tools to continuously analyse and monitor the ABR bitrates. We also pay attention to audio quality, as our ears are sensitive to glitches. For our international customers we offer subtitles, and this flows automatically through the video workflow.

Looking towards the future, the transcoding landscape is rapidly changing as the current H.264 codec offers reduced efficiency at larger screen resolutions. There are several interesting approaches to extend the life of H.264, although it is starting to be replaced at 1080p and higher resolutions by H.265 with savings of between 25-40% observed.

Thank you for reading. In the next article to be published next week, I'll delve into packaging and unwrap the mysteries of DASH and HLS.

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