Video: Reducing peak bandwidth for OTT

‘Flattening the curve’ isn’t just about dealing with viruses, we learn from Will Law. Rather, this is one way to deal with network congestion brought on by the rise in broadband use during the global lockdown. This and other key ways such as per-title encoding and removing the top tier are just two other which are explored in this video from Akamai and Bitmovin.

Will starts the talk explaining why congestion happens in a world where ABR (adaptive bitrate streaming) is supposed to deal with this. With Akamai’s traffic up by around 300%, it’s perhaps not a surprise there’s a contest for bandwidth. As not all traffic is a video stream, congestion will still happen when fighting with other, static, data transfers. However deeper than that, even with two ABR streams, the congestion protocol in use has a big impact as will shows with a graph showing Akamai’s FastTCP and BBR where BBR steals all the bandwidth rather than ‘playing fair’.

Using a webpage constructed for the video, Will shows us a baseline video playback and the metrics associated with it such as data transferred and bitrate which he uses to demonstrate the different benefits of bitrate production techniques. The first is covered by Bitmovin’s Sean McCarthy who explains Bitmovin’s per-title encoding technology. This approach ensures that each asset has encoder settings tuned to get the best out of the content whilst reducing bandwidth as opposed to simply setting your encoder to a fairly-high, safe, static bitrate for all content no matter how complex it is. Will shows on the demo that the bitrate reduces by over 50%.

Swapping codec, is an obvious way to reduce bandwidth. Unlike per-title encoding which is transparent to the end user, using AV1, VP9 or HEVC requires support by the final device. Whilst you could offer multiple versions of your assets to make sure you still cover all your players despite fragmentation, this has the downside of extra encoding costs and time.

Will then looks at three ways to reduce bandwidth by stopping the highest-bitrate rendition from being used. Method one is to manually modify the manifest file. Method two demonstrates how to do so using the Bitmovin player API, and method three uses the CDN itself to manipulate the manifests. The advantage of doing this in the CDN is because this allows much more flexibility as you can use geolocation rules, for example, to deliver different manifests to different locations.

The final method to reduce peak bandwidth is to use the CDN to throttle download speed of the stream chunks. This means that while you may – if you are lucky – have the ability to download at 100Mbps, the CDN only delivers 3- or 5-times the real-time bitrate. This goes a long way to smoothing out the peaks which is better for the end user’s equipment and for the CDN. Seen in isolation, this does very little, as the video bitrate and the data transferred remain the same. However delivering the video in this much more co-operative way is much more likely to cause knock-on problems for other traffic. It can, of course, be used in conjunction with the other techniques. The video concludes with a Q&A.

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Speakers

Will Law Will Law
Chief Architect,
Akamai
Sean McCarthy Sean McCarthy
Technical Product Marketing Manager,
Bitmovin

Video: How CBS Sports Digital streams live events at scale

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

Video: Edge Compute

Delivering personalised video at scale, live or otherwise, is a tradeoff between speed and complexity. In this lightning talk at Demuxed 2019, Kyle Boutette from Cloudflare explains the benefits of running code on the ‘edge’.

Kyle starts by highlighting the reason to use CDNs; they take the management of a whole fleet of servers off your hands allowing you to concentrate on delivering a video service and deploying the technology to do just that. This works really well and CDNs are the backbone of most of the large sites on the internet. Some companies build their own whilst some use Cloudflare or Amazon CloudFront among the many CDNs out there. Apart from dealing with the admin of the servers, CDNs are careful to provide servers as close to your users as practical which helps in reducing latency.

The problem that Kyle exposes is that any personalisation needs to be done on the player itself or on the server. The former requiring implementing the same features on many platforms, the latter destroying the value of the CDN since it’s based on needing the central server(s) to calculate the new information and send it to the CDN bringing us back to square one.

The solution that Cloudflare has developed allows javascript to run on the the CDN’s computers, referred to as the ‘edge’. This allows much of the logic to be done close to the consumer and gives the highest chance of reusing CDN assets whilst also reducing the latency of the requests compared to talking to the central server infrastructure. Doing this with javascript provides a well-understood environment for web developers. Kyle provides examples to understand how this can be done with relatively simple code.

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Speaker

Kyle Boutette Kyle Boutette
Systems Engineer,
Cloudflare

Video: Video Caching Best Practices

Caching is a critical element of the streaming video delivery infrastructure. By storing objects as close to the viewer as possible, you can reduce round-trip times, cut bandwidth costs, and create a more efficient delivery chain.

This video brings together Disney, Qwilt and Verizon to understand their best-practices and look at the new Open Caching Network (OCN) working group from the Streaming Video Alliance. This recorded webinar is a discussion on the different aspects of caching and the way the the OCN addresses this.

The talk starts simply by answering “What is a caching server and how does it work?” which helps everyone get on to the same page whilst listening to the answers to “What are some of the data points to collect from the cache?” hearing ‘cache:hit-ratio’, ‘latency’, ‘cache misses’, ‘data coming from the CDN vs the origin server’ as some of the answers.

This video continues by exploring how caching nodes are built, optimising different caching solutions, connecting a cache to the Open Caching Network, and how bettering cache performance and interoperability can improve your overall viewer experience.

The Live Streaming Working Group is mentioned covered as they are working out the parameters such as ‘needed memory’ for live streaming servers and moves quickly into discussing some tricks-of-the-trade, which often lead to a better cache.

There are lots of best practices which can be shared and the an open caching network one great way to do this. The aim is to create some interoperability between companies, allowing small-scale start-up CDNs to talk to larger CDNs. A way for a streaming company to understand that it can interact with ‘any’ CDN. As ever, the idea comes down to ‘interoperability’. Have a listen and judge for yourself!

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Speakers

Eric Klein Eric Klein
Director, Content Distribution – Disney+/ESPN+, Disney Streaming Services
Co-Chair, Open Cache Working Group, Streaming Video Alliance
Yoav Gressel Yoav Gressel
Vice President of R&D,
Qwilt
Sanjay Mishra Sanjay Mishra
Director, Technology
Verizon
Jason Thibeault Jason Thibeault
Executive Director,
Streaming Media Alliance