Will established methods for contributing video streams over the internet be superseded by a shared protocol? Adrian Pennington investigates.
If the broadcast industry is to expand its ability to stream over the public internet it has to overcome a problem of interoperability.
Software codes that manage to smooth wrinkles such as packet loss when transporting video over IP slash the need for expensive private fibre circuits or satellite links, particularly during first mile contribution.
However, the development of these protocols – which also add security and boost low-latency – by individual vendors now risk locking broadcasters into proprietary workflows.
“With so many different protocols that don’t talk to each other broadcasters are at risk of becoming islands,” says Kieran Kunhya, founder and CEO, Open Broadcast Systems. “Content exchange between them was increasingly difficult.”
For example, if your encoder only supports one protocol and you want to stream to a decoder which only works with another protocol then you’re stuck.
This issue has become acute with the increasing need to scale live events.
To cost-effectively stream the London Marathon around the world the BBC would need to connect multiple networks from private and public internet service providers who will each likely have implemented differing proprietary streaming protocol.
“There’s a commercial imperative among broadcasters globally to cut back on the cost of satellite and fibre and B2B content to more unmanaged solutions,” says Kunhya. “Broadcasters will use IP mainly as a back-up delivery mechanism at first before transitioning to IP as their primary means of transmission with a view to reducing or closing satellite transponders. This trend is common even among the highest profile content providers. Everyone needs to get content out to consumers at a lower cost.”
A new format is riding to the rescue. Reliable Internet Stream Transport (RIST) is intended as a vendor neutral specification for an interoperable protocol formed by Video Services Forum (VSF) – the body that played a key role in creating IP standard SMPTE ST 2022-6.
RIST to the rescue
Technically speaking, RIST is not a standard but a set of guidelines built on top of existing standards established by the Internet Engineering Task Force (IETF).
Administrative and marketing body the RIST Forum counts around 50 members including AWS Elemental, Cobalt Digital, Ateme and Nevion.
Net Insight, another RIST supporter, explains, “Currently, equipment manufacturers either default to the most basic protocols, which are not aimed for high quality, high bandwidth transport, or they are locked into vendor specific implementation. RIST was created to bring an interoperable, industry standard where vendors can exchange content across editorial boundaries, meanwhile, ensuring innovation and differentiation in the implementations and feature set.”
The latter point is important since the RIST specs are sufficiently open to ensure that two different implementations will be interoperable.
“Vendors can differentiate their products through implementation of RIST in ways they cannot with proprietary solutions,” says Kunhya, who is also a director of the RIST Forum. “For example, an encoder could be designed with better memory, another with CPU optimization but both knowing that the product will work with any RIST decoder.”
The Forum has made available a free, open-source library, libRIST, for developers to test that their implementations work with the RIST protocol.
Encryption was recently added to the RIST Main Profile, a critical feature that many broadcasters wanted to see included before adoption. Open Broadcast Systems is currently implementing RIST for customers including the BBC.
However, existing streaming protocols - notably Zixi, SRT and VideoFlow - are still being developed and may offer advantages to users which a more common denominator approach like RIST cannot.
Zixi, Haivision and VideoFlow are also backers of the RIST Forum so it would be wrong to characterise them in conflict with RIST although they are competitive with each other. Indeed, there is considerable overlap among third parties keeping their commercial options open and backing combinations of SRT, Zixi and RIST.
It means that users of SRT-enabled product can implement users of Zixi-enabled product within the same workflow provided both use RIST.
“We believe that the challenges RIST and SRT seek to overcome are essentially the same and fundamental to the future of IP broadcast and internet streaming workflows,” says Peter Maag, chief commercial officer and EVP strategic partnerships, Haivision.
Benefits of SRT
SRT (Secure Reliable Transport) developed by Haivision, is free (open source) and has over 350 members in its Alliance.
Maag argues that the main competitive advantage which media customers of SRT have over using RIST is that, in addition to SMPTE 2022-7 style redundancy, SRT’s connection bonding provides a main/backup mode.
“This allows seamless switching without losing a single packet while avoiding the transmission of redundant data over the different network paths,” he says. “SRT offers the flexibility to operate in three different modes for live streaming, file transfer and message transfer.”
”RIST was created to bring an interoperable, industry standard where vendors can exchange content across editorial boundaries, meanwhile, ensuring innovation and differentiation in the implementations and feature set.” - Net Insight
Haivision has implemented RIST on various products in engineering tests but have yet to see market demand to support RIST.
When it comes to trading off against Zixi, Haivision points to the growing body of users backing its technology.
“SRT is the most widely adopted protocol for performance streaming and is growing fast,” Maag claims. “SRT is community developed continuously by over 60 active open source contributors that are addressing real-world challenges, unhindered by committee process and commercial objectives. The documented open source code is available to use and implement by anybody, right now.”
Aside from use in contribution and distribution (to affiliates, MVPDs, OTT platforms, CDNs), SRT is also used for connecting cloud-based broadcast services and micro-services.
“This is the most over-looked and powerful requirement in the industry,” he says. “Most people don’t realize that, even within a data centre, transferring low latency video between services is subject to packet loss and security concerns. SRT provides the protection to ensure that your video always looks great.”
Benefits of Zixi
Zixi was first to market in this field a decade ago and claims industry leadership. It points to over 180 OEM and service provider partners with more than 20,000 channels delivered daily to 100,000 endpoints. Among recent tech partnerships are the cloud editing solutions Vimond and Blackbird.
“Zixi is a well-established technology with a rich partner and customer ecosystem,” explains Huw Dymond, Director of Product and Operations, Blackbird. “We recognise that we need to fit within a much larger ecosystem and, as such, interoperability is of paramount importance. Ultimately, it comes down to ingesting native standards and outputting native standards faster than the competition and with less reliance on needing to bounce content via secondary processes and workflows.”
Dymond adds that “increasing interest in alternatives like SRT will lead to more requirements to integrate SRT into a Blackbird workflow.”
Zixi also offers Zixi RIST, an implementation of the shared protocol with additional features provided by the Zixi protocol. The company has also been working with one time rival VideoFlow outside of the RIST initiative to ensure compatibility between their protocols and products.
Kunhya acknowledges that “Zixi is a very powerful and advanced protocol with its own merits such as huge product ecosystem, AWS Mediaconnect integration [but] the advantage of RIST is interoperability.”
Another key advantage of RIST and SRT over Zixi is that they do not require a license to use.
Watch Rist members demonstrations:
Source of disagreement
Haivision joined the RIST Activity Group (AG) right at the start of RIST’s development and, according to Kunhya, proposed SRT as an option for the nascent interoperable protocol.
“The experts in the AG vetted the protocol, found it to be lacking, and designed something better,” Kunhya says.
“RIST is the best of all worlds as it has been developed using well understood standards from other industries as well as by companies who know how to do professional packet recovery. SRT was developed in isolation by a single company, based on an old file transfer protocol [UDT]. The result is that RIST has much better performance than SRT, is more secure, and it is a lot simpler to deploy and maintain.”
Kunhya further argues that Haivision is pitching SRT as a prosumer proposition for streaming (such as for eSports delivered over Twitch) and that RIST will become the professional transport solution (analogous to MPEG-2).
“When you have high value content with millions of viewers you need features that RIST has. Use of multiple ISPs being the most important one,” Kunhya says. “SRT is being pitched for contribution applications, and indeed they are rivals in this arena, but RIST is the far better solution. SRT has been around longer, but RIST is making inroads primarily due to its technical superiority.”
Haivision disagrees. “SRT is being adopted primarily by broadcast solutions developers and the broadcast community,” Maag says. “SRT was created to replace broadcast satellite contribution, and that’s something that can fit in both professional broadcast and prosumer markets. We also see SRT as a modern alternative to RTMP – and certainly many companies are looking at it for that reason, too.
“We don’t believe that either RIST or SRT are more or less suitable for either professional or prosumer,” Maag continues. “They are both suitable. We’re in close contact with the most important vendors and customers through the SRT Alliance, which is constantly growing, and we are getting the feedback that SRT is developing as a de facto standard in professional contribution. Every month, more and more companies join and implement SRT into their solutions.”
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