Video: CMAF Live Media Ingest Protocol Masterclass

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

Video: Don’t let latency ruin your longtail: an introduction to “dref MP4” caching

So it turns out that simply having an .mp4 file isn’t enough for low-latency streaming. In fact, for low latency streaming, MP4s work well, but for very fast start times, there’s optimisation work to be done.

Unified Streaming’s Boy van Dijk refers to how mp4s are put together (AKA ISO BMFF) to explain how just restructuring the data can speed up your time-to-play.

Part of the motivation to optimise is the financial motivation to store media on Amazon’s S3 which is relatively cheap and can deal with a decent amount of throughput. This costs latency, however. The way to work around this, explains Boy, is to bring the metadata out of the media so you can cache it separately and, if possible, elsewhere. Within the spec is the ability to bring the index information out of the original media and into a separate file called the dref, the Data Reference box.

Boy explains that by working statelessly, we can see why latency is reduced. Typically three requests would be needed, but we can save those if we just make one, moreover, stateless architectures scale better.

The longtail of your video library is affected most by this technique as it is, by proportion, the largest part, but gets the least requests. Storing the metadata closer, or in faster storage ca vastly reduce startup times. DREF files point to media data allowing a system to bring that closer. For a just-in-time packaging system, drefs works as a middle-man. The beauty is that a DREF for a film is only a few 10s of MB for a film of many gigabytes.

Unified Origin, for different tests, saw reductions of 1160ms->15, 185ms->13 and 240ms->160ms. Depending on what exactly was being tested which Boy explains in the talk in more detail. Overall they have shown that there’s a non-trivial improvement in startup delay.

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Download a detailed presentation

Boy van Dijk Boy van Dijk
Streaming Solutions Engineer,
Unified Streaming

Video: Low Latency Streaming

There are two phases to reducing streaming latency. One is to optimise the system you already have, the other is to move to a new protocol. This talk looks at both approaches achieving parity with traditional broadcast media through optimisation and ‘better than’ by using CMAF.

In this video from the Northern Waves 2019 conference, Koen van Benschop from Deutsche Telekom examines the large and low-cost latency savings you can achieve by optimising your current HLS delivery. With the original chunk sizes recommended by Apple being 10 seconds, there are still many services out there which are starting from a very high latency so there are savings to be had.

Koen explains how the total latency is made up by looking at the decode, encode, packaging and other latencies. We quickly see that the player buffer is one of the largest, the second being the encode latency. We explore the pros and cons of reducing these and see that the overall latency can fall to or even below traditional broadcast latency depending, of course, on which type (and which country’s) you are comparing it too.

While optimising HLS/DASH gets you down to a few seconds, there’s a strong desire for some services to beat that. Whilst the broadcasters themselves may be reticent to do this, not wanting to deliver online services quicker than their over-the-air offerings, online sports services such as DAZN can make latency a USP and deliver better value to fans. After all, DAZN and similar services benefit from low-second latency as it helps bring them in line with social media which can have very low latency when it comes to key events such as goals and points being scored in live matches.

Stefan Arbanowski from Fraunhofer leads us through CMAF covering what it is, the upcoming second edition and how it works. He covers its ability to use .m3u8 (from HLS) and .mpd (from DASH) playlist/manifest files and that it works both with fMP4 and ISO BMFF. One benefit from DASH is it’s Common Encryption standard. Using this it can work with PlayReady DRM, Fairplay and others.

Stefan then takes a moment to consider WebRTC. Given it proposes latency of less than one second, it can sound like a much better idea. Stefan outlines concerns he has about the ability to scale above 200,000 users. He then turns his attention back to CMAF and outlines how the stream is composed and how the player logic works in order to successfully play at low latency.

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Koen van Benschop Koen van Benschop
Senior Manager TV Headend and DRM,
Deutsche Telekom
Stefan Arbanowski Stefan Arbanowski
Director Future Applications and Media,
Fraunhofer FOKUS

Video: Specification of Live Media Ingest

“Standardisation is more than just a player format”. There’s so much to a streaming service than the video, a whole ecosystem needs to work together. In this talk from Comcast’s Mile High Video 2019, we see how different parts of the ecosystem are being standardised for live ingest.

RTMP and Smooth streaming are being phased out – without proper support for HEVC, VVC, HDR etc. they are losing relevance as well as, in the case of RTMP, support from the format itself. Indeed it’s clear that fragmented MP4 (fMP4) and CMAF are taking hold in their place so it makes sense for a new ingest standard to coalesce around these formats.

Rufael Mekuria from Unified streaming explains this effort to create a spec around live media ingest that is happening as part of MPEG DASH-IF. The work itself started at the end of 2017 with the aim of publishing summer 2019 supporting CMAF and DASH/HLS interfaces.

Rufael explains CMAF ingest used HTTP post to move each media stream to the origin packager. The tracks are separated into video, audio, timed text, subtitle and timed metadata. They are all transferred on separate tracks and is compatible with future codecs. He also covers security and timed text before covering DASH/HLS ingest which can also contain CMAF because HLS contains the capability to contain CMAF.

Reference software is available along with the <a href=”http://”” rel=”noopener noreferrer” target=”_blank”>specification.

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