Video: ATSC 3.0 Seminar Part III

ATSC 3.0 is the US-developed set of transmission standards which is fully embracing IP technology both over the air and for internet-delivered content. This talk follows on from the previous two talks which looked at the physical and transmission layers. Here we’re seeing how IP throughout has benefits in terms of broadening choice and seamlessly moving from on-demand to live channels.

Richard Chernock is back as our Explainer in Chief for this session. He starts by explaining the driver for the all-IP adoption which focusses on the internet being the source of much media and data. The traditional ATSC 1.0 MPEG Transport Stream island worked well for digital broadcasting but has proven tricky to integrate, though not without some success if you consider HbbTV. Realistically, though, ATSC see that as a stepping stone to the inevitable use of IP everywhere and if we look at DVB-I from DVB Project, we see that the other side of the Atlantic also sees the advantages.

But seamlessly mixing together a broadcaster’s on-demand services with their linear channels is only benefit. Richard highlights multilingual markets where the two main languages can be transmitted (for the US, usually English and Spanish) but other languages can be made available via the internet. This is a win in both directions. With the lower popularity, the internet delivery costs are not overburdening and for the same reason they wouldn’t warrant being included on the main Tx.

Richard introduces ISO BMFF and MPEG DASH which are the foundational technologies for delivering video and audio over ATSC 3.0 and, to Richard’s point, any internet streaming services.

We get an overview of the protocol stack to see where they fit together. Richard explains both MPEG DASH and the ROUTE protocol which allows delivery of data using IP on uni-directional links based on FLUTE.

The use of MPEG DASH allows advertising to become more targeted for the broadcaster. Cable companies, Richard points out, have long been able to swap out an advert in a local area for another and increase their revenue. In recent years companies like Sky in the UK (now part of Comcast) have developed technologies like Adsmart which, even with MPEG TS satellite transmissions can receive internet-delivered targeted ads and play them over the top of the transmitted ads – even when the programme is replayed off disk. Any adopter of ATSC 3.0 can achieve the same which could be part of a business case to make the move.

Another part of the business case is that ATSC not only supports 4K, unlike ATSC 1.0, but also ‘better pixels’. ‘Better pixels’ has long been the way to remind people that TV isn’t just about resolution. ‘Better pixels’ includes ‘next generation audio’ (NGA), HDR, Wide Colour Gamut (WCG) and even higher frame rates. The choice of HEVC Main 10 Profile should allow all of these technologies to be used. Richard makes the point that if you balance the additional bitrate requirement against the likely impact to the viewers, UHD doesn’t make sense compared to, say, enabling HDR.

Richard moves his focus to audio next unpacking the term NGA talking about surround sound and object oriented sound. He notes that renderers are very advanced now and can analyse a room to deliver a surround sound experience without having to place speakers in the exact spot you would normally need. Options are important for sound, not just one 5.1 surround sound track is very important in terms of personalisation which isn’t just choosing language but also covers commentary, audio description etc. Richard says that audio could be delivered in a separate pipe (PLP – discussed previously) such that even after the
video has cut out due to bad reception, the audio continues.

The talk finishes looking at accessibility such as picture-in-picture signing, SMPTE Timed Text captions (IMSC1), security and the ATSC 3.0 standards stack.

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Speaker

Richard Chernock Richard Chernock
Former CSO,
Triveni Digital

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

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 MPEG-DASH by working to imrove 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.

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Speakers

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

Video: CMAF and DASH-IF Live ingest protocol

Of course without live ingest of content into the cloud, there is no live streaming so why would we leave such an important piece of the puzzle to an unsupported protocol like RTMP which has no official support for newer codecs. Whilst there are plenty of legacy workflows that still successfully use RTMP, there are clear benefits to be had from a modern ingest format.

Rufael Mekuria from Unified Streaming, introduces us to DASH-IF’s CMAF-based live ingest protocol which promises to solve many of these issues. Based on the ISO BMFF container format which underpins MPEG DASH. Whilst CMAF isn’t intrinsically low-latency, it’s able to got to much lower latencies than standard HLS, for instance.

This work to create a standard live ingest protocol was born out of an analysis, Rufael explains, of which part of the content delivery chain were most ripe for standardisation. It was felt that live ingest was an obvious choice partly because of the decaying RTMP protocol which was being sloppy replaced by individual companies doing their own thing, but also because there everyone contributing in the same way is of a general benefit to the industry. It’s not typically, at the protocol level, an area where individual vendors differentiate to the detriment of interoperability and we’ve already seen the, then, success of RMTP being used inter-operably between vendor equipment.

MPEG DAHS and HLS can be delivered in a pull method as well as pushed, but not the latter is not specified. There are other aspects of how people have ‘rolled their own’ which benefit from standardisation too such as timed metadata like ad triggers. Rufael, explaining that the proposed ingest protocol is a version of CMAF plus HTTP POST where no manifest is defined, shows us the way push and pull streaming would work. As this is a standardisation project, Rufael takes us through the timeline of development and publication of the standard which is now available.

As we live in the modern world, ingest security has been considered and it comes with TLS and authentication with more details covered in the talk. Ad insertion such as SCTE 35 is defined using binary mode and Rufael shows slides to demonstrate. Similarly in terms of ABR, we look at how switching sets work. Switching sets are sets of tracks that contain different representations of the same content that a player can seamlessly switch between.

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Speaker

Rufael Mekuria Rufael Mekuria
Head of Research & Standardisation,
Unified Streaming

Video: Reasons to cry –  living room device app development

HbbTV is a transmission standard seeking to unify over-the-air transmissions and broadband-delivered services into a seamless service. This aim is the same as ATSC 3.0 though the means of achieving it are not the same. HbbTV has seen growing use since its debut in 2006 and is now on its 2nd iteration.

James Williams has spent a lot of time getting services working on HbbTV-compliant hardware. STB manufacturers always have to balance very carefully the cost of the box against the components and hence performance. This leads to some unfortunate compromises when it comes to ‘secondary features’ such as rendering HTML, CSS or Javascript even if they are required in order to validate a box against a standard. This talk is a synthesis of what’s he’s learnt, fought against and endured making, sometimes very simple, things work.

James starts by looking at the boxes available and, importantly, the SDKs behind them which are many and varied. We’re then taken through some of the XML necessary to get an HbbTV app up and running including some key “dos and don’ts”. Now that we’ve seen how to invoke a program, James takes us on an amusing journey into getting a loading spinner to work and the many attempts, all highly reasonable, to convince this to be rendered.

For a video service, playing videos is probably the most important function so next we look at the surprising number of ways one can fail to get video to play using quite rational parameters in MPEG DASH seeing the ways to make it work and the ones to avoid. Finally we see the variety of responses that boxes report back their failure to render video.

A cautionary tale, or a guide to survive? You decide.
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Speaker

James Williams James Williams
Solutions Engineer,
Mux