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Video: CMAF with ByteRange – A Unified & Efficient Solution for Low Latency Streaming

Posted on 13th July 2021 by Russell Trafford-Jones

Apple’s LL-HLS protocol is the most recent technology offering to deliver low-latency streams of just 2 or 3 seconds to the viewer. Before that, CMAF which is built on MPEG DASH also enabled low latency streaming. This panel with Ateme, Akamai and THEOplayer asks how they both work, their differences and also maps out a way to deliver both at once covering the topic from the perspective of the encoder manufacturer, the CDN and the player client.

We start with ATEME’s Mickaël Raulet who outline’s CMAF starting with its inception in 2016 with Microsoft and Apple. CMAF was published in 2018 and most recently received detailed guidelines for low latency best practice in 2020 from the DASH Industry Forum. He outlines that the idea of CMAF is to build on DASH to find a single way of delivering both DASH and HLS using once set of media. THe idea here is to minimise hits on the cache as well as storage. Harnessing the ISO BMFF CMAF adds on the ability to break chunks in to fragments opening up the promise of low latency delivery.

Mickaël discusses the methods of getting hold of these short fragments. If you store the fragments separately, then you double your storage as 4 fragments make up a whole segment. So it’s better to have all the fragments written as a segment. We see that Byterange requests are the way forward whereby the client asks the server to start delivering a file from a certain number of bytes into the file. We can even request this ahead of time, using a preload hint, so that the server can push this data when it’s ready.

Next we hear from Akamai’s Will Law who examines how Apples LL-HLS protocol can work within the CDN to provide either CMAF for LL-HLS from the same media files. He uses the example of a 4-second segments with four second-long parts. A standard latency player would want to download the whole 4-second segment where as a LL-HLS player would want the parts. DASH, has similar requirements and so Will focusses on how to bring all of these requirements down into the mimum set of files needed which he calls a ‘common cache footprint’ using CMAF.

He shows how byterange requests work, how to structure them and explains that, to help with bandwidth estimation, the server will wait until the whole of the byterange is delivered before it sends any data thus allowing the client to download a wire speed. Moreover a single request can deliver the rest of the segments meaning 7 requests get collapsed into 1 or 2 requests which is an important saving for CDNs working at scale. It is possible to use longer GOPs for a 4-second video clip than for 1-second parts, but for this technique to work, it’s important to maintain the same structure within the large 4-second clip as in the 1-second parts.

THEOplayer’s Pieter-Jan Speelmans takes the floor next explaining his view from the player end of the chain. He discusses support for LL-HLS across different platforms such as Android, Android TV, Roku etc. and concludes that there is, perhaps surprisingly, fairly wide support for Apple’s LL-HLS protocol. Pieter-Jan spends some time building on Will’s discussion about reducing request numbers for browsers, CORS checking can increase cause extra requests to be needed when using Byterange requests. For implementing ABR, it’s important to understand how close you are to the available bandwidth. Pieter-Jan says that you shouldn’t only use the download time to determine throughput, but also metadata from the player to get as an exact estimate as possible. We also hear about dealing with subtitles which can need to be on screen longer than the duration of any of the parts or even of the segment length. These need to be adapted so that they are shown repeatedly and each chunk contains the correct information. This can lead to flashing on re-display so, as with many things in modern players, needs to be carefully and intentionally dealt with to ensure the correct user experience.

The last part of the video is a Q&A which covers:

Use of HTTP2 and QUIC/HTTP3

Dynamic Ad Insertion for low latency

The importance of playlist blocking

Player synchronisation with playback rate adjustment

Player analytics

DRM insertion problems at low-latency

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Speakers

	Will Law Chief Architect, Edge Technology Group, Akamai
	Mickaël Raulet CTO, ATEME
	Pieter-Jan Speelmans CTO & Founder, THEOPlayer

Video: CMAF Live Media Ingest Protocol Masterclass

Posted on 6th May 2021 by Russell Trafford-Jones

We’ve heard before on The Broadcast Knowledge about CMAF’s success at bringing down the latency for live dreaming to around 3 seconds. CMAF is standards based and works with Apple devices, Android, Windows and much more. And while that’s gaining traction for delivery to the home, many are asking whether it could be a replacement technology for contribution into the cloud.

Rufael Mekuria from Unified Streaming has been working on bringing CMAF to encoders and packagers. All the work in the DASH Industry forum has centred around to key points in the streamin architecture. The first is on the output of the encoder to the input of the packager, the second between the packager and the origin. This is work that’s been ongoing for over a year and a half, so let’s pause to ask why we need a new protocol for ingest.

RTMP and Smooth streaming have not been deprecated but they have not been specified to carry the latest codecs and while people have been trying to find alternatives, they have started to use fragmented MP4 and CMAF-style technologies for contribution in their own, non-interoperable ways. Push-based DASH and HLS are common but in need of standardisation and in the same work, support for timed metadata such as splice information for ads could be addressed.

The result of the work is a method of using a separate TCP connection for each essence track; there is a POST command for each subtitles stream, metadata, video etc. This can be done with fixed length POST, but is better achieved with chunked tranfer encoding.

Rufael next shows us an exmaple of a CMAF track. Based on the ISO BMFF standard, CMAF specifies which ‘boxes’ can be used. The CMAF specification provides for optional boxes which would be used in the CMAF fragements. Time is important so is carried in ‘Live basemedia decodetime’ which is a unix-style time stamp that can be inserted into both the fragment and the CMAF header.

With all media being sent separately, the standard provides a way to define groups of essences both implicitly and explicity. Redundancy and hot failover have been provided for with multiple sources ingesting to multiple origins using the timestamp synchronisation, identical fragments can be detected.

The additional timed metadata track is based on the ISO BMFFF standard and can be fragmented just like other media. This work has extended the standard to allow the carrying of the DASH EventMessageBox in the time metadata track in order to reuse existing specifications like id3 and SCTE 214 for carrying SCTE 35 messages.

Rufael finishes by explaining how SCTE messages are inserted with reference to IDR frames and outlines how the DASH/HLS ingest interface between the packager and origin server works as well as showing a demo.

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Speaker

Rufael Mekuria
Head of Research & Standardisation,
Unifed Streaming

Video: CMAF And The Future Of OTT

Posted on 12th October 2020 by Russell Trafford-Jones

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

Video: CMAF and DASH-IF Live ingest protocol

Posted on 6th March 2020 by Russell Trafford-Jones

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 and LHLS.

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 DASH 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