Ali C. Begen Archives – The Broadcast Knowledge

Video: Demystifying Video Delivery Protocols

Posted on 30th July 2020 by Russell Trafford-Jones

Let’s face it, there are a lot of streaming protocols out there both for contribution and distribution. Internet ingest in RTMP is being displaced by RIST and SRT, whilst low-latency players such as CMAF and LL-HLS are vying for position as they try to oust HLS and DASH in existing services streaming to the viewer.

This panel, hosted by Jason Thibeault from the Streaming Video Alliance, talks about all these protocols and attempts to put each in context, both in the broadcast chain and in terms of its features. Two of the main contribution technologies are RIST and SRT which are both UDP-based protocols which implement a method of recovering lost packets whereby packets which are lost are re-requested from the sender. This results in a very high resilience to packet loss – ideal for internet deployments.

First, we hear about SRT from Maxim Sharabayko. He lists some of the 350 members of the SRT Alliance, a group of companies who are delivering SRT in their products and collaborating to ensure interoperability. Maxim explains that, based on the UDT protocol, it’s able to do live streaming for contribution as well as optimised file transfer. He also explains that it’s free for commercial use and can be found on github. SRT has been featured a number of times on The Broadcast Knowledge. For a deeper dive into SRT, have a look at videos such as this one, or the ones under the SRT tag.

Next Kieran Kunhya explains that RIST was a response to an industry request to have a vendor-neutral protocol for reliable delivery over the internet or other dedicated links. Not only does vendor-neutrality help remove reticence for users or vendors to adopt the technology, but interoperability is also a key benefit. Kieran calls out hitless switching across multiple ISPs and cellular. bonding as important features of RIST. For a summary of all of RIST’s features, read this article. For videos with a deeper dive, have a look at the RIST tag here on The Broadcast Knowledge.

Demystifying Video Delivery Protocols from Streaming Video Alliance on Vimeo.

Barry Owen represents WebRTC in this webinar, though Wowza deal with many protocols in their products. WebRTC’s big advantage is sub-second delivery which is not possible with either CMAF or LL-HLS. Whilst it’s heavily used for video conferencing, for which it was invented, there are a number of companies in the streaming space using this for delivery to the user because of it’s almost instantaneous delivery speed. Whilst a perfect rendition of the video isn’t guaranteed, unlike CMAF and LL-HLS, for auctions, gambling and interactive services, latency is always king. For contribution, Barry explains, the flexibility of being able to contribute from a browser can be enough to make this a compelling technology although it does bring with it quality/profile/codec restrictions.

Josh Pressnell and Ali C Begen talk about the protocols which are for delivery to the user. Josh explains how smoothstreaming has excited to leave the ground to DASH, CMAF and HLS. They discuss the lack of a true CENC – Common Encryption – mechanism leading to duplication of assets. Similarly, the discussion moves to the fact that many streaming services have to have duplicate assets due to target device support.

Looking ahead, the panel is buoyed by the promise of QUIC. There is concern that QUIC, the Google-invented protocol for HTTP delivery over UDP, is both under standardisation proceedings in the IETF and is also being modified by Google separately and at the same time. But the prospect of a UDP-style mode and the higher efficiency seems to instil hope across all the participants of the panel.

Watch now to hear all the details!
Speakers

	Ali C. Begen Technical Consultant, Comcast
	Kieran Kunhya Founder & CEO, Open Broadcast Systems Director, RIST Forum
	Barry Owen VP, Solutions Engineering Wowza Media Systems
	Josh Pressnell CTO, Penthera Technologies
	Maxim Sharabayko Senior Software Developer, Haivision
	Moderator: Jason Thibeault Executive Director, Streaming Video Alliance

Video: Bandwidth Prediction for Multi-Bitrate Streaming at Low Latency

Posted on 24th July 2020 by Russell Trafford-Jones

Low latency protocols like CMAF are wreaking havoc with traditional ABR algorithms. We’re having to come up with new ways of assessing if we’re running out of bandwidth. Traditionally, this is done by looking at how long a video chunk takes to download and comparing that with its playback duration. If you’re downloading at the same speed it’s playing, it’s time consider changing stream to a lower-bandwidth one.

As latencies have come down, servers will now start sending data from the beginning of a chunk as it’s being written which means it’s can’t be downloaded any quicker. To learn more about this, look at our article on ISO BMFF and this streaming primer. Since the file can’t be downloaded any quicker, we can’t ascertain if we should move up in bitrate to a better quality stream, so while we can switch down if we start running out of bandwidth, we can’t find a time to go up.

Ali C. Begen and team have been working on a way around this. The problem is that with the newer protocols, you pre-request files which start getting sent when they are ready. As such you don’t actually know the time the chunk starts downloading to you. Whilst you know when it’s finished, you don’t have access, via javascript, to when the file started being sent to you robbing you of a way of determining the download time.

Ali’s algorithm uses the time the last chunk finished downloading in place of the missing timestamp figuring that the new chunk is going to load pretty soon after the old. Now, looking at the data, we see that the gap between one chunk finishing and the next one starting does vary. This lead Ali’s team to move to a sliding window moving average taking the last 3 download durations into consideration. This is assumed to be enough to smooth out some of those variances and provides the data to allow them to predict future bandwidth and make a decision to change bitrate or not. There have been a number of alternative suggestions over the last year or so, all of which perform worse than this technique called ACTE.

In the last section of this talk, Ali explores the entry he was part of into a Twitch-sponsored competition to keep playback latency close to a second in test conditions with varying bitrate. Playback speed is key to much work in low-latency streaming as it’s the best way to trim off a little bit of latency when things are going well and allows you to buy time if you’re waiting for data; the big challenge is doing it without the viewer noticing. The entry used a heuristics and a machine learning approach which worked so well, they were runners up in the contest.

Watch now!
Speaker

Ali C. Begen,
Technical Consultant, Comcast
Professor, Computer Science, Özyeğin University

Video: DASH: from on-demand to large scale live for premium services

Posted on 6th April 2020 by Russell Trafford-Jones

A bumper video here with 7 short talks from VideoLAN, Will Law and Hulu among others, all exploring the state of MPEG DASH today, the latest developments and the hot topics such as low latency, ad insertion, bandwidth prediction and one red-letter feature of DASH – multi-DRM.

The first 10 minutes sets the scene introducing the DASH Industry Forum (DASH IF) and explaining who takes part and what it does. Thomas Stockhammer, who is chair of the Interoperability Working Group explains that DASH IF is made of companies, headline members including Google, Ericsson, Comcast and Thomas’ employer Qualcomm who are working to promote the adoption of MPEG-DASH by working to improve the specification, advise on how to put it into practice in real life, promote interoperability, and being a liaison point for other standards bodies. The remaining talks in this video exemplify the work which is being done by the group to push the technology forward.

Meeting Live Broadcast Requirements – the latest on DASH low latency!
Akamai’s Will Law takes to the mic next to look at the continuing push to make low-latency streaming available as a mainstream option for services to use. Will Law has spoken about about low latency at Demuxed 2019 when he discussed the three main file-based to deliver low latency DASH, LHLS and LL-HLS as well as his famous ‘Chunky Monkey’ talk where he explains how CMAF, an implementation of MPEG-DASH, works in light-hearted detail.

In today’s talk, Will sets out what ‘low latency’ is and revises how CMAF allows latencies of below 10 seconds to be achieved. A lot of people focus on the duration of the chunks in reducing latency and while it’s true that it’s hard to get low latency with 10-second chunk sizes, Will puts much more emphasis on the player buffer rather than the chunk size themselves in producing a low-latency stream. This is because even when you have very small chunk sizes, choosing when to start playing (immediately or waiting for the next chunk) can be an important part of keeping the latency down between live and your playback position. A common technique to manage that latency is to slightly increase and decrease playback speed in order to manage the gap without, hopefully, without the viewer noticing.

Chunk-based streaming protocols like HLS make Adaptive Bitrate (ABR) relatively easy whereby the player monitors the download of each chunk. If the, say, 5-second chunk arrives within 0.25 seconds, it knows it could safely choose a higher-bitrate chunk next time. If, however, the chunk arrives in 4.8 seconds, it can choose to the next chunk to be lower-bitrate so as to receive the chunk with more headroom. With CMAF this is not easy to do since the segments all arrive in near real-time since the transferred files represent very small sections and are sent as soon as they are created. This problem is addressed in a later talk in this talk.

To finish off, Will talks about ‘Resync Elements’ which are a way of signalling mid-chunk IDRs. These help players find all the points which they can join a stream or switch bitrate which is important when some are not at the start of chunks. For live streams, these are noted in the manifest file which Will walks through on screen.

Ad Insertion in Live Content:Pre-, Mid- and Post-rolling
Whilst not always a hit with viewers, ads are important to many services in terms of generating the revenue needed to continue delivering content to viewers. In order to provide targeted ads, to ensure they are available and to ensure that there is a record of which ads were played when, the ad-serving infrastructure is complex. Hulu’s Zachary Cava walks us through the parts of the infrastructure that are defined within DASH such as exchanging information on ‘Ad Decision Parameters’ and ad metadata.

In chunked streams, ads are inserted at chunk boundaries. This presents challenges in terms of making sure that certain parameters are maintained during this swap which is given the general name of ‘Content Splice Conditioning.’ This conditioning can align the first segment aligned with the period start time, for example. Zachary lays out the three options provided for this splice conditioning before finishing his talk covering prepared content recommendations, ad metadata and tracking.

Bandwidth Prediction for Multi-bitrate Streaming at Low Latency
Next up is Comcast’s Ali C. Begen who follows on from Will Law’s talk to cover bandwidth prediction when operating at low-latency. As an example of the problem, let’s look at HTTP/1.1 which allows us to download a file before it’s finished being written. This allows us to receive a 10-second chunk as it’s being written which means we’ll receive it at the same rate the live video is being encoded. As a consequence, the time each chunk takes to arrive will be the same as the real-time chunk duration (in this example, 10 seconds.) When you are dealing with already-written chunks, your download time will be dependent on your bandwidth and therefore the time can be an indicator of whether your player should increase or decrease the bitrate of the stream it’s pulling. Getting back this indicator for low-latency streams is what Ali presents in this talk.

Based on this paper Ali co-authored with Christian Timmerer, he explains a way of looking at the idle time between consecutive chunks and using a sliding window to generate a bandwidth prediction.

Implementing DASH low latency in FFmpeg
Open-source developer Jean-Baptiste Kempf who is well known for his work on VLC discusses his work writing an MPEG-DASH implementation for FFmpeg called the DASH-LL. He explains how it works and who to use it with examples. You can copy and paste the examples from the pdf of his talk.

Managing multi-DRM with DASH
The final talk, ahead of Q&A is from NAGRA discussing the use of DRM within MPEG-DASH. MPEG-DASH uses Common Encryption (CENC) which allows the DASH protocol to use more than one DRM scheme and is typically seen to allow the use of ‘FairPlay’, ‘Widevine’ and ‘PlayReady’ encryption schemes on a single stream dependent on the OS of the receiver. There is complexity in having a single server which can talk to and negotiate signing licences with multiple DRM services which is the difficulty that Lauren Piron discusses in this final talk before the Q&A led by Ericsson’s VP of international standards, Per Fröjdh.

Watch now!
Speakers

	Thomas Stockhammer Director of Technical Standards, Qualcomm
	Will Law Chief Architect, Akamai
	Zachary Cava Software Architect, Hulu
	Ali C. Begen Technical Consultant, Video Architecture, Strategy and Technology group, Comcast
	Jean-Baptiste Kempf President & Lead VLC Developer VideoLAN
	Laurent Piron Principal Solution Architect NAGRA
	Moderator: Per Fröjdh VP International Standards, Ericsson

Video: Bandwidth Prediction in Low-Latency Chunked Streaming

Posted on 19th August 2019 by Russell Trafford-Jones

How can we overcome one of the last, big, problems in making CMAF 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.

Watch now!

Speaker

Ali C. Begen
Technical Consultant and
Computer Science Professor

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