Sienna NDI Insider Know-How Series

with Mark Gilbert, CTO Gallery SIENNA

 

 

Part 4 - NDI over SRT Protocol

 

Transport Protocols used for Remote Video Workflows

Today we will discuss some very important concepts for remote video contribution and monitoring.

 

Traditional "Haivision Makito Style" SRT

Many typical customer remote workflows are based on traditional "SRT"  by which we mean H.264 or HEVC with AAC audio in an MPEG Transport stream then wrapped in SRT.

These connections are generally fairly compressed, and incur a certain amount of encoding, decoding and other latencies.  They can also be heavy on CPU/GPU when a computer is involved at one/both ends, and there are a number of tricky considerations when using multichannel audio, or real time metadata.  Nevertheless, this is probably the most common contribution protocol and works extremely well with Sienna.

 

Higher Data Rate Connections, for Tier 1 broadcast

Some broadcasters have struggled to accept traditional SRT (typically at 10-30 mbits/sec) for their premium workflows, and they have insisted on a high data rate remote connection - in these cases, typically dark fibre running native 2110 uncompressed, or JPEGXS is common, also JPEG2000 connections.

These types of connection are typically in the hundreds of mBit/sec range even up to multi GBit/sec, which is possible because these broadcasters typically deploy leased fibre lines, or AWS direct connect infrastructure at 10Gbit or more.

Whilst these applications provide better picture quality, and generally lower latency, the costs of the connection infrastructure, and particularly the encoding or decoding devices or licenses can be very high, and implementing stream redundancy or fault tolerance can add to costs.

 

Is there an alternative, which provides the best of both worlds ?  - Yes,  NDI over SRT

A less well known option is built into Sienna ND Processing Engine Advanced - NDI over SRT.   This differs significantly from the "Traditional SRT" referenced above because, whilst it uses the same SRT protection wrapper and connection protocols, it uses native Full NDI High Bandwidth data inside the SRT wrapper, which of course yields a much higher data rate.  This means that a native NDI source at one end, can be carried seamlessly, and reliably across the public internet (provided both ends have appropriate bandwidth), and emitted at the other end as the same pristine NDI source, with no transcoding along the way.   The main benefits are super-low latency,  full, unmodified picture quality,  support for unlimited audio channels, and bidirectional metadata (including PTZ control).

 

In effect its similar to a native NDI connection, but without any of the problems associated with trying to run NDI over wide area networks which include :

- Requirements to open large blocks of ports on the sending end since NDI uses random port selection

- Open Ports are always required at the sending side and at the discovery side.

- Complications with NDI Discovery across networks

- Video stuttering or failure to stream caused by latency and startup network flooding.

 

Instead, NDI Over SRT is designed specifically for Wide Area networks and in contrast features :

- One single open UDP port is all you need per stream, on which ever side is most convenient, regardless of stream direction.

- No requirement for NDI Discovery

- Proper WAN protocol with 'soft start' technology to work seamlessly over long distance internet connections to achieve smooth and reliable video.

 

Sienna has demonstrated NDI over SRT in the most extreme workflows, such as transporting UHDp60 in Native NDI Full bandwidth 280mBit/s from Google Cloud in USA to AWS in Europe with tiny latency and 100% reliability.  NDI over SRT can carry NDI High Bandwidth,  HX2 or HX3 formats, so you have a scalable transport from a few megabits all the way to hundreds of megabits using the same infrastructure.

 

The Target Audience

Broadcasters already using or considering things like JPEGXS workflows may be very receptive to using NDI over SRT as an alternative, given many benefits

- Much less expensive to acquire

- Much less expensive to operate

- Native NDI at both ends to integrate seamlessly with cameras, vision mixers etc without additional conversions.

- No "per channel" costs other than bandwidth - compute load is very low since no transcoding occurs.

- Software only infrastructure suitable for virtualisation.

 

What is needed for NDI over SRT ?

NDI over SRT is included with the Sienna ND Processing Engine Advanced Tier.  This includes a "Transmit" and a "Receive" module, which can operate in caller or listener modes.

You will require a Sienna ND Processing Engine at both ends of the transport connection, but remember the CPU load is super low so very powerful hardware is optional.

Something new, just released this week is the NDI over SRT Monitor for Apple TV 4K - this acts as a stand alone remote monitor end point for the NDI over SRT protocol. It connects to a remote ND Processing Engine and receives an NDI over SRT stream using caller mode, which is displayed via the Apple TV HDMI output.  It also emits a localised NDI stream of the remote source.

 

Summary :

During conversations about JPEGXS, direct connect and other high data rate remote video connections, make sure you are primed with all the information about NDI over SRT so you can speak with authority and determine if it's appropriate for your application.

 

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