Low Latency Dash also known as LL-DASH is a modification of MPEG DASH to allow it to operate with close to two seconds’ latency bringing it down to meet, or beat, standard broadcast signals.
Brightcove’s Bo Zhang starts by outlining the aims and methods of getting there. For instance, he explains, the HTTP 1.1 Chunked Transfer element is key to low-latency streaming as it allows the server to start sending a video segment as its being written, not waiting until the file is complete. LL-DASH also has the ability to state an availability window (‘availabilityTimeOffset’).
As LL-MPEG DASH is a living standard, there are updates on the way: Resync points will allow a player to receive a list of places where it can join a stream using SAP types in the ISO-BMFF spec, the server can send a ‘service description’ to the player which can use the information to adjust its latency. Event messages can now be inserted in the middle of segments.
Bo then moves on to explain that he and the team have set up and experiment to gain experience with LL-DASH and test overall latency. He shows that they decided to stream RTMP out of OBS, into a github project called ‘node-gpac-dash’ then to the dash.js player all. between Boston and Seattle. This test runs at 800×600, 30fps with a bitrate of 2.5Mbps and shows results of between 2.5 and 5 seconds depending on the network conditions.
As Bo moves towards the Q&A, he says that low-latency streaming is less scalable because a TCP connection needs to be kept open between the player and the CDN which is a burden.
Another compromise is that smaller chunk sizes in LL-DASH give reduced latency but IO increases meaning sometimes you may have to increase the chunk sizes (and hence latency of the stream) to allow for better performance. He also adds that adverts are more difficult with low-latency streams due to the short amount of time to request and receive the advertising.
Multicast ABR (mABR) is a way of delivering traditional HTTP-based streams like HLS and DASH over multicast. On a managed telco network, the services are multicast to thousands of homes and only within the home itself does the stream gets converted back unicast HTTP. Devices in the home then access streaming services in exactly the same way as they would Netflix or iPlayer over the internet, but the content is served locally. Streaming is a point-to-point service so each device takes its own stream. If you have 3 devices in the home watching a service, you’ll be sending 3 streams out to them. With mABR, the core network only ever sees one stream to the home and the linear scaling is done internally. Not only does this help remove peaks in traffic, but it significantly reduces the load on the upstream networks, the origin servers and smooths out the bandwidth use.
This video from DVB lays out the business cases which are enabled by mABR. mABR has approved the specification which is now going for standardisation within ETSI. It’s already gained some traction with deployments in the field, so this talk looks at what the projects that drive the continued growth in mABR may look like.
Williams Tovar starts first by making the case for OTT over satellite. With OTT services continuing to take viewing time away from traditional broadcast services, satellite providers are working to ensure they retain relevance and offer value. Delivering these OTT services is, thus, clearly beneficial, but why would you want to? On top of the mABR benefits briefly outlined above, this business case recognises that not everyone is served by a good internet connection. Distributing OTT by satellite can provide high bitrate, OTT experiences to areas with bad broadband and could also be an efficient way to deliver to large public places such as hotels and ships.
Julian Lemotheux from Orange presents a business case for next-generation IPTV. The idea here is to bring down the cost of STBs by replacing CA security with DRM and replacing the chipset with a cheaper one which is less specialised. As DASH and HLS streaming are cpu-based tasks and well understood, general, mass-produced chipsets can be used which are cheaper and removing CA removes some hardware from the box. Also to be considered is that the OTT ecosystem is continually seeing innovation so delivering services in the same format allows providers to keep their offerings up to date without custom development in the IPTV software stack.
Xavier Leclercq from Broadpeak looks, next, at Scaling ABR Delivery. This business case is a consideration of what the ultimate situation will be regarding MPEG2 TSes and ABR. Why don’t we provide all services as Netflix-style ABR streams? One reason is that the scale is enormous with one connection per device, CDNs and national networks would still not be able to cope. Another is that the QoS for MPEG2 transport streams is very good and, whilst it is possible to have bad reception, there is little else that causes interruption to the stream.
mABR can address both of these challenges. By delivering one stream to each home and having the local gateway do the scaling, mass delivery of streamed content becomes both predictable and practical. Whilst there is still a lot of bandwidth involved, the predictable load on the CDNs is much more controlled and with lower peaks, the CDN cost is reduced as this is normally based on the maximum throughput. mABR can also be delivered with a higher QoS than public internet traffic which allows it to benefit from better reliability which could move it in the realm of the traditional transport-stream based serviced. Xavier explains that if you put the gateway within a TV, you are able to deliver a set-top-box-less service whilst if you want to address all devices in you home, you can provide a separate gateway.
Before the video finishes with a Q&A session, Williams delivers the business case for Backhauling over Satellite for CDNs and IP backhaul for 5G Networks. The use case for both has similarities. The CDN backhauling example looks at using satellite to efficiently deliver directly to CDN PoPs in hard to reach areas which may have limited internet links. The Satellite could deliver a high bandwidth set of streams to many PoPs. A similar issue presents itself as there is so much bandwidth available, there is a concern about getting enough into the transmitter. Whether by satellite or IP Multicast, mABR could be used for CDN backhauling to 5G networks delivering into a Mobile Edge Computing (MEC) cache. A further benefit in doing this is avoiding issues with CDN and core network scalability where, again, keeping the individual requests and streams away from the CDN and the network is a big benefit.
RIST continues to gain traction as a way to deliver video reliably over the internet. Reliable Internet Stream Transport continues to find uses both as part of the on-air signal chain and to enable broadcast workflows by ensuring that any packet loss is mitigated before a decoder gets around to decoding the stream.
In this video, AWS Elemental’s David Griggs explains why AWS use RIST and how RIST works. Introduced by LearnIPvideo.com’s Will Simpson who is also the co-chair of the RIST Activity Group at the VSF. Wes starts off by explaining the difference between consumer and business use-cases for video streaming against broadcast workflows. Two of the pertinent differences being one-directional video and needing a fixed delay. David explains that one motivator of broadcasters looking to the internet is the need to replace C-Band satellite links.
RIST’s original goals were to deliver video reliably over the internet but to ensure interoperability between vendors which has been missing to date in the purest sense of the word. Along with this, RIST also aimed to have a low, deterministic latency which is vital to make most broadcast workflows practical. RIST was also designed to be agnostic to the carrier type being internet, satellite or cellular.
Wes outlines how important it is to compensate for packet loss showing that even for what might seem low packet loss situations, you’ll still observe a glitch on the audio or video every twenty minutes. But RIST is more than just a way of ensuring your video/audio arrives without gaps, it. can also support other control signals such as PTZ for cameras, intercom feeds, ad insertion such as SCTE 35, subtitling and timecode. This is one strength which makes RIST ideal for broadcast over using, say RTMP for delivering a live stream.
Wes covers the main and simple profile which are also explained in more detail in this video from SMPTE and this article. One way in which RIST is different from other technologies is GRE tunnelling which allows the carriage of any data type alongside RIST and also allows bundling of RIST streams down a single connecting. This provides a great amount of flexibility to support new workflows as they arise.
David closes the video by explaining why RIST is important to AWS. It allows for a single protocol to support media transfers to, from and within the AWS network. Also important, David explains, is RIST’s standards-based approach. RIST is created out of many standards and RFC with very little bespoke technology. Moreover, the RIST specification is being formally created by the VSF and many VSF specifications have gone on to be standardised by bodies such as SMPTE, ST 2110 being a good example. AWS offer RIST simple profile within MediaConnect with plans to implement the main profile in the near future.
Will streaming really be any better with 5G? What problems won’t 5G solve? Just a couple of the questions in this panel from the Streaming Video Alliance. There are so many aspects of 5G which are improvements, it can be very hard to clearly articulate for a given use case which are the main ones that matter. In this webinar, the use case is clear: streaming to the consumer.
Moderating the session, Dom Robinson kicks off the conversation asking the panellists to dig below the hype and talk about what 5G means for streaming right now. Brian Stevenson is first up explaining that the low-bandwidth 5G option really useful as it allows operators to roll out 5G offerings with the spectrum they already have and, given its low frequency, get a good decent a propagation distance. In the low frequencies, 5G can still give a 20% improvement bandwidth. Whilst this is a good start, he continues, it’s really delivering in the mid-band – where bandwidth is 6x – that we can really start enabling the applications which are discussed in the rest of the talk.
Humberto la Roche from Cisco says that in his opinion, the focus needs to be on low-latency. Latency at the network level is reduced when working in the millimetre wavelengths, reducing around 10x. This is important even for video on demand. He points out, though that delay happens within the IP network fabric as well as in the 5G protocol itself and the wavelength it’s working on. Adding buffers into the network drives down the cost of that infrastructure so it’s important to look at ways of delivering the overall latency needed at a reasonable cost. We also hear from Sanjay Mishra who explains that some telcos are already deploying millimetre wavelengths and focussing on advancing edge compute in high-density areas as their differentiator.
The panel discusses the current technical challenges for operators. Thierry Fautier draws from his experience of watching sports in the US on his mobile devices. The US has a zero-rating policy, he explains, where a mobile operator waives all data charges when you use a certain service, but only delivers the video at SD resolution at 1.5 Mbps. Whilst the benefits to this are obvious, it means that as people buy new, often larger phones, with better screens, they expect to reap the benefits. At SD, Thierry says, you can’t see the ball in Tennis, so there 5G will offer the over-the-air network bandwidth needed to allow the telcos to offer HD as part of these deals.
The panel discusses the problems seen so far in delivering MBMS – multicast for mobile networks. MBMS has been deployed sporadically around the world in current LTE networks (using eMBMS) but has faced a typical chicken and egg problem. Given that both cell towers and mobile devices need to support the technology, it hasn’t been worth the upgrade cost for the telcos given that eMBMS is not yet supported by many chipsets including Apple’s. Thierry says there is hope for a 5G version of MBMS since Apple is now part of the 3GPP.
CMAF had a similar chicken and egg situation when it was finalised, there was hesitance in using it because Apple didn’t support it. Now with iOS 14 supporting HLS in CMAF, there is much more interest in deploying such services. This is just as well, cautions Thierry, as all the talk of reduced latency in 5G or in the network itself won’t solve the main problem with streaming latency which exists at the application layer. If services don’t abandon HLS/DASH and move to LL-HLS and LL-DASH/CMAF then the improvements in latency lower down the stack will only convey minimal benefits to the viewer.
Sanjay discusses the problem of coverage and penetration which will forever be a problem. “All cell towers are not created equal.” The challenge will remain as to how far and wide coverage will be there.
The panel finishes looking at what’s to come and suggests more ‘federations’ of companies working together, both commercially and technically, to deliver video to users in better ways. Thierry sums up the near future as providing higher quality experiences, making in-stadia experiences great and enabling immersive video.
President-Chair at Ultra HD Forum
VP Video Strategy Harmonic at Harmonic
Moderator: Dom Robinson
Co-Founder, Director, and Creative Firestarter
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