03.07.2020 | Ausgabe 07/2020

The VSF RIST Profile Reduces Streaming Costs

In 2017, at that year’s VidTrans conference a regional gathering of members of the Video Services Forum (VSF), a new protocol for delivering audio and video over lossy IP networks (including the public Internet), was born. It was an idea that many had been skeptical of, since the open Internet brought with it all kinds of quality, security, latency and reliability issues.
Proponents argued that the benefits of reduced cost by using COTS hardware and avoiding renting expensive private network bandwidth (via H.264 and H.265 compression) to deliver live streams for sporting and corporate events, outweighed the negatives. Another advantage is that is it agnostic to bit rate or resolution formats. A broadcaster could send HD video one day and 4K video the next over the same networked system architecture. So quality was not an issue either.
RIST developers said it was intended as a more reliable and open successor to the Secure Reliable Transport (SRT) video transport protocol as well as an open-spec and open-source alternative to proprietary commercial options. And, they predicted correctly, things would only get better as technology improved.

At an interoperability test of third-party technology, the Reliable Internet Stream Transport (RIST) Protocol Specification was tested and published publicly. RIST, they said, was designed to provide a common industry specification for low-latency live video contribution over the Internet. A RIST Activity Group was set up within the VSF to spearhead development efforts.
The benefit of RIST is that it is an industry specification that is supported by many companies, rather than being a proprietary protocol designed by one vendor or another. That allows customers to pick the product they want to use and know that it will work with other RIST-compatible devices.
While developing the new spec, the RIST Activity Group said one of its goals was to avoid inventing anything new if it didn’t have to. For example the SMPTE 2022-2 standard, designed for compressed video transmission, is supported in RIST.
Basically, SMPTE 2110 assumes that the network is error free, so there are mechanisms in the ST 2110 spec to compensate for this. However, at its fundamental layer, it sends each pixel once and that’s it. With RIST, it’s assumed that the network is going to lose packets somewhere along the delivery chain and so the VSF has figured out a way to intelligently retransmit those packets that have gone missing.

Using the RIST spec, each packet that goes out has a sequence number associated with it. Specialized software algorithms looks for gaps in the sequence numbers at the receiver. If packets become lost, the receiver sends a message back to the transmitter instructing it to send only those lost packets. This way a file transfer or live video stream is guaranteed to arrive at the correct time, in the correct package.
The protocol continues to develop. In April the VSF released new technical recommendations for RIST, called Technical Recommendation TR-06-2:2020. This adds to the RIST Simple Profile (TR-06-01, released in 2018), adding features such as support for in-band data, encryption, authentication, and bandwidth optimization. It also supports high bitrate streams, making it possible to use RIST for uncompressed or lightly compressed content.
The VSF says that whenever possible, RIST Main Profile is built on top of existing Requests For Comments and Standards to ease implementation. This is especially important for encryption and authentication, since the use of proven, widely implemented technologies greatly improves the security of the solution. Richard Friedel, EVP, Engineering, Fox Television Stations and current VSF president, said that Main Profile RIST now provides critical encryption and security capabilities that work across multiple vendors, enabling high-quality, live video broadcasting using standard Internet connections. He added that as media companies seek to produce content from an ever-multiplying range of new locations, RIST offers a flexible set of capabilities while allowing content to be easily shared across terrestrial and cloud platforms as well.

At the 2019 IBC show last fall, VSF member companies—which now number more than 20, including broadcast networks like CBS, ESPN and Fox, as well as technology vendors like Artel, Cobalt Digital, Dolby, DVEO, Evertz, Nevion, Panasonic, Sony, Videoflow, Qvidium and Zixi – participated in a successful demonstration of Main Profile. This demo was followed by an interoperability test in February 2020 by many of the same vendors, culminating in a live, trans-oceanic demonstration conducted at the VidTrans 2020 conference (February 25-27) at the Marina Del Rey Marriott, Los Angeles, CA.
The latest features of RIST Main Profile provide a set of capabilities that give users the ability to operate and control every stream with reliability, flexibility and security. They are now working on the new RIST Enhanced Profile, said to be considering features like auto-configuration, adaptive encoding, and support for satellite links.
At the end of the day, RIST was created by a panel of experts from multiple companies, and it has benefited greatly from their combined experience. Current results of a series of live tests have been very positive, and several remote productions of sporting events have been successfully completed. While it’s not an ideal file transport solution for everyone, compressed file delivery works for a lot of users – especially in light of the current stay-at-home mandates being carried out around the world. The VSF has promised that future versions of the RIST spec will include additional features that cover a wider range of user applications.
The VSF Technical Recommendation spec now includes the minimum set of capabilities that any software or hardware system must implement in order to be considered RIST-compliant. The spec is available for free download at https://vsf.tv/technical_recommendations.shtml.


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