Video: Beam hopping in DVB-S2X

Posted on by Russell Trafford-Jones

Beam hopping is the relatively new ability of a satellite to move its beam so that it’s transmitting to a different geographical area every few milliseconds. This has been made possible by the advance of a number of technologies inside satellite which make this fast, constant, switching possible. DVB is harnessing this new capability to more efficiently deliver bandwidth to different areas.

This talk starts off with a brief history of DVB-S2 moving to DVB-S2X and the successes of that move. But we then see that geographically within a wide beam, two factors come in to play: The satellite throughput is limited by the amplifiers and TWTs, plus certain areas within the beam needed more throughput than others. By dynamically pointing a more focused beam using ferrite switches and steerable antennae – to name but two technologies at play – we see that up to 20% of unmet demand could be addressed.

The talk continues with the ESA’s Nader Alagha explaining some of the basics of directing beams talking about moving from cells and clusters (geographical areas) and then how ‘dwell times’ are the amount of time spent at each cell. He then moves on to give an overview of the R&D work underway and the expected benefits.

A little like in older CRT Televisions a little gap needs to be put into the signal to cover the time the beam is moving. For analogue television this is called ‘blanking’, for stellites this is an ‘idle sequence’. Each time a beam hopes, the carrier frequency, bandwidth and number of carriers can change.

Further topics explored are implementing this on geostationary and non-geostationary satellites, connecting hopping strategy to traffic and the channel models that can be created around beam hopping. The idea of ‘superframes’ is detailed where frames that need to be decoded with a very low SNR, the information is spread out and duplicated an number of times. This is supported in beam hopping with some modifications which require some pre-ambles and the understanding of fragmentation of these frames.

The talk closes discussing looking at future work and answering questions from the webinar attendees.

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Speakers

Nader Alagha Nader Alagha
Senior Communications Engineer,
ESA ESTEC (European Space Research and Technology Centre)
Peter Nayler Peter Nayler
Business Manager,
EASii IC
Avi Freedman
Director of System Engineering,
Satixfy

Video: S-Frame in AV1: Enabling better compression for low latency live streaming.

Posted on by Russell Trafford-Jones

Streaming is such a success because it manages to deliver video even as your network capacity varies while you are watching. Called ABR (Adaptive Bitrate), this short talk asks how we can allow low-latency streams to nimbly adapt to network conditions whilst keeping the bitrate low in the new AV1 codec.

Tarek Amara from Twitch explains the idea in AV1 of introducing S-Frames, sometimes called ‘switch frames’, which take the role of the more traditional I or IDR frames. If a frame is marked as an IDR frame, this means the decoder knows it can start decoding from this frame without worrying that it’s referencing some data that came before this frame. By doing this, you can allow frequent points at which a decoder can enter a stream. IDR frames are typically I frames which are the highest bandwidth frames, by a large proportion. This is because they are a complete rendition of a frame without any of the predictions you find in P and B frames.

Because IDR frames are so large, if you want to keep overall bandwidth down, you should reduce the number of them. However, reducing the number of frames reduces the number if ‘in points’ for for the stream meaning a decoder then has to wait longer before it can start displaying the stream to the viewer. An S-Frame brings the benefits of an IDR in that it still marks a place in the stream where the decoder can join, free of dependencies on data previously sent. But the S-Frame is takes up much less space.

Tarek looks at how an S-Frame is created, the parameters it needs to obey and explains how the frames are signalled. To finish off he presents tests run showing the bitrate improvements that were demonstrated.
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Speaker

Tarek Amara Tarek Amara
Engineering Manager, Video Encoding,
Twitch

Webinar: RAVENNA and its Relationship to AES67 and SMPTE ST 2110

Posted on by Russell Trafford-Jones


This webinar is now available on-demand

This first in a series of webinars, this will have a broad scope covering the history of audio networking in, the development of RAVENNA the the consequent developments of AES67 and ST2110. Whether you’re new to or already familiar with RAVENNA and/or AES67 & ST2110 you’ll benefit from this webinar either as revision or as an excellent starting point for understanding the landscape of Audio-over-IP standards and technologies.

This webinar is presented Andreas Hildebrand who has previously appeared on The Broadcast Knowledge giving insight into The Audio Parts of ST 2110, ST 2110-30 and NMOS IS-08 — Audio Transport and Routing amongst others.

This talk looks at how audio IP works and the benefits of using an IP system. Since the invention of RAVENNA, the AES and SMPTE have moved to using audio over IP so the walk will examine how RAVENNA and SMPTE place the audio data on the network and get that to the decoders. Interoperability between systems is important but can only happen if certain parameters are correct, something that Andreas will mention but will also be a subject for future webinars.

Whether you want to revise the basics from an expert or learn them for the first time, now’s the time to register.

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Speaker

Andreas Hildebrand Andreas Hildebrand
Senior Product Manager,
ALC NetworX GmbH

Video: How CBS Sports Digital streams live events at scale

Posted on by Russell Trafford-Jones

Delivering high scale in streaming really exposes the weaknesses of every point of your workflow, so even those of us who are not streaming at maximum scale, there are many lessons to be learnt. CBS Sports Digital delivered the Super Bowl using the principles of ‘practice, practice, practice’, keeping the solution as simple as possible and making mitigation of problems primary to solving them.

Taylor Busch tells walks us through their solution explaining how it supported their key principles and highlighting the technology used. Starting with Acquisition, he covers the SDI fibre delivery to a backup facility as well as the AWS Direct Connect links for their Elemental Live encoders. The origin servers were in two different regions and both received data from both sets of encoders.

CBS used ‘Output locking’ which ensures that the TS segments are all aligned even across different encoders which is done by respecting the timecode in the SDI and helps in encoder failover situations. QVBR encoding is a method of encoding up to a quality level rather than simply saying ‘7000 kbps’. QVBR provides a more efficient use a bandwidth since in the situations where a scene doesn’t require a lot of bandwidth, it won’t be sent. This variability, even if you run in capped mode to limit the bandwidth of particularly complex scenes, can look like a failing encoder to some systems, so the fact this is now in ‘VBR’ mode, needs to be understood by all the departments and companies who monitor your feed.

Advertising is famously important for the Super Bowl, so Taylor gives an overview of how they used the CableLabs ESAM protocol and SCTE to receive information about and trigger the adverts. This combined SCTE-104, ESAM and SCTE-35 as we’ll as allowing clients to use VAST for tracking. Extra caching was provided by Fastly’s Media Shield which tests for problems with manifests, origin servers and encoders. This fed a Multi-CDN setup using 4 CDNs which could be switched between. There is a decision point for requests to determine which CDN should answer.

Taylor then looks at the tools, such as Mux’s dashboard, which they used to spot problems in the system; both NOC-style tools and multiviewers. They set up three war rooms which looked at different aspects of the system, connectivity, APIs etc. This allowed them to focus on what should be communicated keeping ‘noise’ down to give people the space they needed to do their work at the same time as providing the information required. Taylor then opens up to questions from the floor.

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Speaker

Taylor Busch, Sr. Taylor Busch
Senior Director Engineering,
CBS Sports Digital