Video: 2019 What did I miss? – Introducing Reliable Internet Streaming Transport

By far the most visited video of 2019 was the Merrick Ackermans’ review of RIST first release. RIST, the Reliable Internet Stream Transport protocol, aims to be an interoperable protocol allowing even lossy networks to be used for mission-critical broadcast contribution. Using RIST can change a bade internet link into a reliable circuit for live programme material, so it’s quite a game changer in terms of cost for links.

An increasing amount of broadcast video is travelling over the public internet which is currently enabled by SRT, Zixi and other protocols. Here, Merrick Ackermans explains the new RIST specification which aims to allow interoperable internet-based video contribution. RIST, which stands for Reliable Internet Stream Transport, ensures reliable transmission of video and other data over lossy networks. This enables broadcast-grade contribution at a much lower cost as well as a number of other benefits.

Many of the protocols which do similar are based on ARQ (Automatic Repeat-reQuest) which, as you can read on wikipedia, allows for recovery of lost data. This is the core functionality needed to bring unreliable or lossy connections into the realm of usable for broadcast contribution. Indeed, RIST is an interesting merging of technologies from around the industry. Many people use Zixi, SRT, and VideoFlow all of which can allow safe contribution of media. Safe meaning it gets to the other end intact and un-corrupted. However, if your encoder only supports Zixi and you use it to deliver to a decoder which only supports SRT, it’s not going to work out. The industry as accepted that these formats should be reconciled into a shared standard. This is RIST.

File-based workflows are mainly based on TCP (Transmission Control Protocol) although, notably, some file transfer service just as Aspera are based on UDP where packet recovery, not unlike RIST, is managed as part of the the protocol. This is unlike web sites where all data is transferred using TCP which sends an acknowledgement for each packet which arrives. Whilst this is great for ensuring files are uncorrupted, it can impact arrival times which can lead to live media being corrupted.

RIST is being created by the VSF – the Video Standards Forum – who were key in introducing VS-03 and VS-04 into the AIMS group on which SMPTE ST 2022-6 was then based. So their move now into a specification for reliable transmission of media over the internet has many anticipating great things. At the point that this talk was given the simple profile has been formed. Whist Merrick gives the details, it’s worth pointing out that this doesn’t include intrinsic encryption. It can, of course, be delivered over a separately encrypted tunnel, but an intrinsic part of SRT is the security that is provided from within the protocol.

Despite Zixi, a proprietary solution, and Haivision’s open source SRT being in competition, they are both part of the VSF working group creating RIST along with VideoFlow. This is because they see the benefit of having a widely accepted, interoperable method of exchanging media data. This can’t be achieved by any single company alone but can benefit all players in the market.

This talk remains true for the simple profile which just aims to recover packets. The main protocol, as opposed to ‘simple’, has since been released and you can hear about it in a separate video here. This protocol adds FEC, encryption and other aspects. Those who are familiar with the basics may whoosh to start there.

Speaker

Merrick Ackermans Merrick Ackermans
Chair,
VSF RIST Activity Group

Video: The next enhancement for RIST

Continuing the look at RIST, the developing protocol which allows for reliable streaming over the internet – even in the event of packet loss, we have a look at a key feature on the roadmap.

The core proposition of RIST is to produce an interoperable protocol which brings the internet into the list of ways to contribute and distribute low-latency video. It’s resilient to packet loss due to it’s ability to re-request packets which have been lost yet is light enough for video streaming. In another talk at IBC, we learn about the latest developments which have added security and many other features to the list of capabilities.

Here, Adi Rozenberg from VideoFlow explains how this will further be extended by upcoming work to allow the source stream to reduce in bitrate in response to reduced capacity in the network. With RIST’s ARQ – the technology which requests missing packets – we find that the retransmissions can actually aggravate bitrate constrictions particularly when they are permanent. Adi proposes the only real way to solve lack of bandwidth issues is to reduce the bitrate of the source.

RIST already includes NULL packet removal so that NULL packets aren’t transmitted and are re-inserted at the remote end. This is usually a great start in reducing the bitrate of the stream. However more is needed, we need a way to tell the encoder to reduce the bandwidth of the video stream itself. This can be accomplished by RTCP.

Adi identifies the problem of identifying when extra bandwidth has returned as a reduction of bandwidth is quickly and easily signalled with retransmissions, but excess bandwidth silently returns. The system gradually increases the encoder bandwidth to always be probing the current balance of bandwidth and bitrate.

This works well when there is a single encoder and a single decoder. When there are multiple decoders, life is more difficult. The solution offered to this is to create a ladder of bitrates all of which are adaptable. Now the destination can switch between profiles. This can be extended to MPTS (Multi-Program Transport Streams) whereby, depending on the destination, services in the MPTS are dropped in order to recover bandwidth. A mechanism is used which prioritises services depending on the destination (i.e. German channels are de-prioritised on delivery to France).

The session ends with a Q&A on stream switching details and use in stat mixing.

Watch now!
Speakers

Adi Rozenberg Adi Rozenberg
CTO,
VideoFlow

Video: RIST – Introducing Reliable Internet Streaming Transport

An increasing amount of broadcast video is travelling over the public internet which is currently enabled by SRT, Zixi and other protocols. Here, Merrick Ackermans explains the new RIST specification which aims to allow interoperable internet-based video contribution. RIST, which stands for Reliable Internet Stream Transport, ensures reliable transmission of video and other data over lossy networks. This enables broadcast-grade contribution at a much lower cost as well as a number of other benefits.

RIST is an interesting merging of technologies from around the industry. Many people use Zixi, SRT, and VideoFlow all of which can allow safe contribution of media. Safe meaning it gets to the other end intact and un-corrupted. However, if your encoder only supports Zixi and you use it to deliver to a decoder which only supports SRT, it’s not going to work out. The industry as accepted that these formats should be reconciled into a shared standard. This is RIST.

RIST is being created by the VSF – the Video Standards Forum – who were key in introducing VS-03 and VS-04 into the AIMS group on which SMPTE ST 2022-6 was then based. So their move now into a specification for reliable transmission of media over the internet has many anticipating great things. At the point that this talk was given the simple profile has been formed. Whist Merrick gives the details, it’s worth pointing out that this doesn’t include intrinsic encryption. It can, of course, be delivered over a separately encrypted tunnel, but an intrinsic part of SRT is the security that is provided from within the protocol.

Despite Zixi, a proprietary solution, and Haivision’s open source SRT being in competition, they are both part of the VSF working group creating RIST along with VideoFlow. This is because they see the benefit of having a widely accepted, interoperable method of exchanging media data. This can’t be achieved by any single company alone but can benefit all players in the market.

This talk remains true for the simple profile which just aims to recover packets. The main protocol, as opposed to ‘simple’, has since been released and you can hear about it in a separate video here. This protocol adds FEC, encryption and other aspects. Those who are familiar with the basics may whoosh to start there.

Watch now!
Download the presentation

Speaker

Merrick Ackermans Merrick Ackermans
Chair,
VSF RIST Activity Group