Video: CMAF And The Future Of OTT

Why is CMAF still ‘the future’ of OTT? Published in 2018, CMAF’s been around for a while now so what are the challenges and hurdles holding up implementation? Are there reasons not to use it at all? CMAF is a way of encoding and packaging media which then can be sent using MPEG DASH and HLS, the latter being the path Disney+ has chosen, for instance.

This panel from Streaming Media West Connect, moderated by Jan Ozer, discusses CMAF use within Akami, Netflix, Disney+, and Hulu. Peter Chave from Akamai starts off making the point that CMAF is important to CDNs because if companies are able to use just one CMAF file as the source for different delivery formats, this reduces storage costs for consumers and makes each individual file more popular thus increasing the chance of having a file available in the CDN (particularly at the edge) and reducing cache misses. They’ve had to do some work to ensure that CMAF is carried throughout the CDN efficiently and ensuring the manifests are correctly checked.

Disney+, explains Bill Zurat, is 100% HLS CMAF. Benefiting from the long experience of the Disney Streaming Services teams (formerly BAMTECH), but also from setting up a new service, Disney were able to bring in CMAF from the start. There are issues ensuring end-device support, but as part of the launch, a number were sunsetted which didn’t have the requirements necessary to support either the protocol or the DRM needed.

Hulu is an aggregator so they have strong motivation to normalise inputs, we hear from Hulu’s Nick Brookins. But they also originate programming along with live streaming so CMAF has an important to play on the way in and the way out. Hulu dynamically regenerates their manifests so can iterate as they roll out easily. They are currently part the way through the rollout and will achieve full CMAF compatibility within the next 18 months.

The conversation turns to DRM. CMAF supports two methods of DRM known as CTR (adopted by Apple) and CBC (also known as CBCS) which has been adopted by others. AV1 supports both, but the recommendation has been to use CBC which appears have been universally followed to date explains Netflix’s Cyril Concolato. Netflix have been using AV1 since it was finalised and are aiming to have most titles transitioned by 2021 to CMAF.

Peter comments from Akamai’s position that they see a number of customers who, like Disney+ and Peacock, have been able to enter the market recently and move straight into CMAF, but there is a whole continuum of companies who are restricted by their workflows and viewer’s devices in moving to CMAF.

Low latency streaming is one topic which invigorates minds and debates for many in the industry. Netflix, being purely video on demand, they are not interested in low-latency streaming. However, Hulu is as is Disney Streaming Services, but Bill cautions us on rushing to the bottom in terms of latency. Quality of experience is improved with extra latency both in terms of reduced rebuffering and, in some cases, picture quality. Much of Disney Streaming Services’ output needs to match cable, rather than meeting over-the-air latencies or less.

The panel session finishes with a quick-fire round of questions from Jan and the audience covering codec strategy, whether their workflows have changed to incorporate CMAF, just-in-time vs static packaging, and what customers get out of CMAF.

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Speakers

Cyril Concolato Cyril Concolato
Senior Software Engineer,
Netflix
Peter Chave Peter Chave
Principal Architect,
Akamai
Nick Brookins Nick Brookins
VP, Platform Services Group,
Hulu
Bill Zurat Bill Zurat
VP, Core Technology
Disney Streaming Services
Jan Ozer Moderator: Jan Ozer
Contributing Editor, Streaming Media
Owner, StreamingLearningCenter.com

Video: Scalable Per-User Ad Insertion in Live OTT

Targetted ads are the most valuable ads, but making sure the right person gets the right ad is tricky, not only in deciding who to show which ad to, but in scaling – and keeping track of – the ad infrastructure to thousands or millions of viewers. This video explains how this complexity arises and the techniques that Hulu have implemented to improve the situation.

Zachary Cava from Hulu lays out the way that standard advertising works for live streams. Whilst he uses MPEG DASH as an example, much the same is true of HLS. This starts with cutting up the video into sections which all start with an IDR frame for seeking. SCTE 35 is used to indicate times when ads can be inserted. These are called SCTE Markers. As DASH has the principle of defining a period (exactly as it sounds, just a way of marking a section of time), we can define periods of ‘programme’ and periods for ‘ads’. This allows the possibility of swapping out a whole period for a section of several ads.

If it were as simple as just swapping out whole periods, that would be Server-Side Ad Insertion. For per-user targetted ads, the streaming service has to keep track of every ad which was given to a user so that when they rewind, they have a consistent experience. This can mean remembering millions of ads for services which have a large rewind buffer. Moreover, traffic can become overwhelming as, since the requests are unique, a CDN can’t help in the caching. Whilst you can scale your system, the cost can spiral up beyond the revenue practical.

Enter MPD Patch Requests. This addition to MPEG Dash requires the client to remember the whole of the manifest. Where the client has a gap in its knowledge, it can simply request that section from the server which generates a ‘diff’, returning only the changes, which the client then assimilates into memory. The benefit here is that all the clients end up converging on only requesting what’s happening ‘now’ and so CDNs come back in to play. Zachary explains how this works in more detail and shows examples before explaining how URLQueryInfo helps reduce the complexity of URL parameters, again in order to interoperate better with CDNs and allows the ad system to be scaled separately to the main video assets.

Finally, Zachary takes a look at coming back from an ad break where you may find that your ads were longer then the ad period allotted or that the programme hasn’t returned before the ads finished. During the ad break, the client is still polling for updates so it’s possible to quickly update the manifest and swap back to programme video early. Similarly at the end of a break, if there is still no content, the server can start issuing its own ad or content, effectively moving back to server-side ad insertion. However, this is not necessarily just plain ad insertion, explains Zachary, rather Hulu cal it ‘Server-Guided’ ad insertion. There is no stitching on the server, but the server is informing you where to get the next video from. It also allows for some levels of user separation where some larger geographies can see different ads to those from other areas.

Zachary finishes by outlining the work Hulu is doing to feedback this learning into the DASH spec, via the DASH Industry Forum and their work with the industry at large to bring more consistency to SCTE 35 markers.

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Speaker

Zachary Cava Zachary Cava
Software Architect,
Hulu

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: Scaling Live OTT with DASH


MPEG DASH is a standard for streaming which provides a stable, open chain for distribution detailing aspects like packaging and DRM as well as being the basis for low-latency CMAF streaming.

DASH Manifest files, text files which list the many small files which make up the stream, can be complicated, long and take a long time to parse, demonstrates Hulu’s Zachary Cava. As the live event continues, the number of chunks to describe increases and so manifest files can easily grow to hundred of KB and eventually to megabytes meaning the standard way of producing these .mpd files will end up slowing the player down to the point it can’t keep up with the stream.

Zachary goes over some initial optimisations which help a lot in reducing the size o the manifests before introducing a method of solving the scalability issue. He explains that patching the mid file is the way to go meaning you can reference just the updated values in the latest .mpd.

With on-secreen examples of manifest files, we clearly see how this works and we see that this method is still compatible with branching of the playback e.g. for regionalisation of advertising or programming.

Zachary finishes by explaining that this technique is arriving in the 4th edition of MPEG-DASH and by answering questions from the audience.

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Speaker

Zachary Cava Zachary Cava
Video Platform Architect.
Hulu