Video: Bandwidth Prediction in Low-Latency Chunked Streaming

How can we overcome one of the last, big, problems in making CMAF a generally available: making ABR work properly.

ABR, Adaptive Bitrate is a technique which allows a video player to choose what bitrate video to download from a menu of several options. Typically, the highest bitrate will have the highest quality and/or resolution, with the smallest files being low resolution.

The reason a player needs to have the flexibility to choose the bitrate of the video is mainly due to changing network conditions. If someone else on your network starts watching some video, this may mean you can no longer download video quick enough to keep watching in full quality HD and you may need to switch down. If they stop, then you want your player to switch up again to make the most of the bitrate available.

Traditionally this is done fairly simply by measuring how long each chunk of the video takes to download. Simply put, if you download a file, it will come to you as quickly as it can. So measuring how long each video chunk takes to get to you gives you an idea of how much bandwidth is available; if it arrives very slowly, you know you are close to running out of bandwidth. But in low-latency streaming, your are receiving video as quickly as it is produced so it’s very hard to see any difference in download times and this breaks the ABR estimation.

Making ABR work for low-latency is the topic covered by Ali in this talk at Mile High Video 2019 where he presents some of the findings from his recently published paper which he co-authored with, among others, Bitmovin’s Christian Timmerer and which won the DASH-IF Excellence in DASH award.

He starts by explaining how players currently behave with low-latency ABR showing how they miss out on changing to higher/lower renditions. Then he looks at the differences on the server and for the player between non-low-latency and low-latency streams. This lays the foundation to discuss ACTE – ABR for Chunked Transfer Encoding.

ACTE is a method of analysing bandwidth with the assumption that some chunks will be delivered as fast as the network allows and some won’t be. The trick is detecting which chunks actually show the network speed and Ali explains how this is done and shows the results of their evaluation.

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Speaker

Ali C. Begen Ali C. Begen
Technical Consultant and
Computer Science Professor

Webinar: Building Tomorrow’s OTT Platforms

Discover the critical success factors the Broadcasters and platform owners, investing millions in building and upgrading OTT platforms, need to achieve to ensure they can compete successfully with a growing array of digital competitors and deliver compelling user experiences.

Many of these broadcasters are beginning to move from their initial OTT offerings to more mature services that can scale for the future, and answer the requirements of demanding viewers and regulators.

This webinar uncovers the essential parts of a flourishing OTT service, including:
– Delivering content at scale as more viewing and live events move to OTT
– Ensuring a class-leading user experience and quality
– Using analytics to maximise revenue and engagement
– Ensuring cost efficiency in the OTT workflow
– Securing platforms and content against piracy and malicious attacks

Register now!

Speakers

Natalie Billingham Natalie Billingham
Vice President, Media & Carrier EMEA,
Akamai
Raphaël Goldwaser Raphaël Goldwaser
Lead Video Architect,
France Télévisions
Chris Wood Chris Wood
Chief Technology Officer,
Spicy Mango

Video: Deploying WebRTC In A Low-Latency Streaming Service

WebRTC is an under appreciated streaming protocol with sub-second latency. Several startups are working hard to harness this technology born by Google for use in video conferencing for live streaming.

When you look at the promised latencies, you can see why. CMAF, the lowest-latency protocol for live streaming using HLS-style chunked file delivery is gaining wider adoption and provides a very impressive latency reduction, however it typically stops at between 4 and 2 seconds. To get below a second, WebRTC is almost the only option out there.

In this talk, Millicast CTO Dr. Alex Gouaillard looks at the misunderstandings and misinformation are out there regarding WebRTC. Dr. Alex covers WebRTC now having ABR, using over multiple hops, the testing ecosystem and much more.

Dr. Alex also covers the lessons learnt over the last two years of development and implementation of the standard and finishes by looking to the future which will bring in QUIC, AV1 and Web ASM

Speaker

Alex Gouaillard Alex Gouaillard
Founder & CTO,
Millicast

Video: What’s the Deal with ALHLS?

Low latency streaming was moving forward without Apple’s help – but they’ve published their specification now, so what does that mean for the community efforts that were already under way and, in some places, in use?

Apple is responsible for HLS, the most prevalent protocol for streaming video online today. In itself it’s a great success story as HLS was ideal for its time. It relied on HTTP which was a tried and trusted technology of the day, but the fact it was file-based instead of a stream pushed from the origin was a key factor in its wide adoption.

As life has moved on and demands have moved from “I’d love to see some video – any video – on the internet!” to “Why is my HD stream arriving after my flat mate’s TV’s?” we see that HLS isn’t quite up to the task of low-latency delivery. Using pure HLS as originally specified, a latency of less than 20 seconds was an achievement.

Various methods were, therefore, employed to improve HLS. These ideas included cutting the duration of each piece of the video, introducing HTTP 1.1’s Chunked Transfer Encoding, early announcement of chunks and many others. Using these, and other, techniques, Low Latency HLS (LHLS) was able to deliver streams of 9 down to 4 seconds.

Come WWDC this year, Apple announced their specification on achieving low latency streaming which the community is calling ALHLS (Apple Low-latency HLS). There are notable differences in Apple’s approach to that already adopted by the community at large. Given the estimated 1.4 billion active iOS devices and the fact that Apple will use adherence to this specification to certify apps as ‘low latency’, this is something that the community can’t ignore.

Zac Shenker from Comcast explains some of this backstory and helps us unravel what this means for us all. Zac first explains the what LHS is and then goes in to detail on Apple’s version which includes interesting, mandatory, elements like using HTTP/2. Using HTTP/2 and the newer QUIC (which will become effectively HTTP/3) is very tempting for streaming applications but it requires work both on the server and the player side. Recent tests using QUIC have been, when taken as a whole, inconclusive in terms of working out whether this it has a positive or a negative impact on streaming performance; experiemnts have shown both results.

The talk is a very good and detailed look at the large array of requirements in this specification. The conclusion is a general surprise at the amount of ‘moving parts’ given there is both significant work to be done on the server as well as the player. The server will have to remember state and due to the use of HTTP/2, it’s not clear that the very small playlist.m3u8 files can be served from a playlist-optimised CDN separately from the video as is often the case today.

There’s a whole heap of difference between serving a flood of large files and delivering a small, though continually updated, file to thousands of end points. As such, CDNs currently optimised separately for the text playlists and the media files they serve. They may even be delivered by totally separate infrastructures.

Zac explains why this changes with ALHLS both in terms of separation but also in the frequency of updating the playlist files. He goes on to explore the other open questions like how easy it will be to integrate Server-Side Add Insertion (SSAI) and even the appetite for adoption of HTTP/2.

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Speaker

Zac Shenker Zac Shenker
Director of Engineering, Video Experience & Optimization,
CBS Interactive