Other articles in this series:

In part two we looked at how NDI developed a suite of tools to better support its pool of vendors and end users, a pool that effectively burst its banks during the Covid pandemic. For most people the beginning of the 2020s was pretty much a shambles, and after a frankly dreadful start to the decade, 2021 started letting in tiny chinks of light. The US rejoined the Paris Climate Accord, Uber drivers in the UK were awarded workers’ rights, and William Shatner became the oldest space traveler in history. Even better, live sporting tournaments started up again and broadcasters were approaching big ticket events like the Superbowl and the 2021 Tokyo Olympics in entirely new ways.

After years of testing, POCs and parallel broadcasts, distributed working became a trusted and valuable professional workflow almost overnight, and for NDI it marked something of a step change. The company literally broadened its horizons in July 2021 with the launch of its NDI 5.0 toolkit. Introducing a number of tools designed to support NDI over wide area networks, NDI 5.0 looked to exploit broadcasters’ shift to remote and distributed production with new tools like NDI Bridge, which allowed NDI to be used over the internet, NDI Remote and NDI Audio Direct. It was a canny move as these technologies aimed to deliver what these new broadcast environments were looking for, and aimed to do so without the complexity of standard, external syncs, and dedicated IP network engineers.

NDI Audio Direct

Initially created as a VST plugin for integrating NDI audio into workflows, NDI Audio Direct was designed to enable users to send and receive audio alongside more established protocols like Dante.

It allows users to create flexible I/O, such as Dante in and NDI out, or vice versa, within the same software application. It is agnostic, supporting various audio codecs such as PCM, AAC, and Opus, and is able to handle unlimited PCM channels – or 255 channels for Opus – bidirectionally in a single stream. It supports any sample rate, will resample if required, and it operates at 32-bit floating point, which the NDI website says ensures high quality and the ability for conversion from various audio formats through APIs on the sender side.

But one of the key distinctions from other IP audio codecs like Dante and ST2110-30 is that NDI Audio Direct doesn’t require any external sync, making it faster to implement and easier to deploy. It works by multiplexing multiple uncompressed audio channels into a single NDI stream to ensure synchronization with each other, and it applies a dynamic buffer scheme to the entire stream that assesses network conditions and sets an appropriate buffer. This ensures that timing within a single NDI audio stream remains consistent and synchronized, irrespective of the number of channels being transmitted.

NDI Audio Direct’s big idea is that, unlike IP codecs where multiple separate audio channels can drift in relation to each other over time depending on unpredictable factors like backhaul transport, it maintains consistent timing between audio channels because the multiplexed channels are effectively handled as a single stream on the network and its buffer mechanism stabilizes the multiplexed stream against transport variations. Although the individual audio channels within an NDI stream are not explicitly synchronized to each other, the buffer scheme ensures that once the stream is established, the timing remains fixed and consistent throughout the broadcast.

Crucially, it is a much simpler way to access remote networks without having to enable multicast in the cloud. NDI is a natively unicast technology, and the combination of NDI Audio Direct and NDI Bridge enables multichannel audio streams to be easily distributed and shared over the internet. This is what is especially appealing to broadcasters and has not gone unnoticed, with adoption by the likes of Eurosport to manage commentary positions, as well as by intercom vendors looking to provide software-driven, wireless connectivity options in the cloud.

Which brings us nicely to NDI Bridge and NDI Remote.

NDI Bridge

The introduction of the Bridge was a big deal for NDI as it allowed users to share NDI sources beyond their local networks and connect independent NDI instances over the internet without having to rely on technologies like SRT for remote transmission. Its aim was to overcome the limitations of local networks by connecting independent NDI infrastructures in different locations, and in doing so to encourage more distributed and cloud-based production workflows.

And by and large, it did bring NDI to the attention of many more broadcasters, attracted by the prospect of connecting remote production teams and encouraging collaboration over reliable WAN connections.

The simplest way to imagine it is as a VPN between different NDI infrastructures, where users can discover and register NDI sources in the same way as they would on a local network. NDI Bridge maintains all the same control and data transfer, including the transport of metadata, tally signals for camera operators, remote PTZ control, Alpha channel support and multi-channel audio. Like all equipment in the NDI ecosystem it is available in embedded devices such as cameras and audio mixers, and is also available as a "headless" NDI Bridge software module that can be integrated into software-first applications.

The expansion from a relatively secure LAN meant that security features were stepped up, including levels of encryption to safeguard streams during transmission, and in keeping with NDI’s long-term strategy, a simplistic user interface limited to just three options; to host a network, join a network, or use the Bridge as a Proxy to transcode other sources.

With the launch of NDI 5.0, NDI Bridge also introduced support for the Reliable User Datagram Protocol (RUDP), a packet-based transport protocol that dates back to the late 1990s. RUDP aims to combine the low latency transport of UDP (User Datagram Protocol) with the reliability of TCP (Transmission Control Protocol) and acts as a relatively effective protocol for real time data for several reasons. By assigning sequence numbers to every packet it sends, RUDP is able to detect missing or out-of-order packets on receipt, and request retransmission of any missing packet when applicable.

RUDP also incorporates flow control mechanisms to manage the rate of data transmission to ensure the network is never overloaded, and dynamically adjusts transmission rates based on network conditions. RUDP acts to mitigate against one of the biggest potential limitations of IP-based transport protocols, which is its dependence on network quality. The quality of the connection – not to mention the capacity of the host computer – plays a huge part in the Quality of Service of NDI, and NDI Bridge undergoes a compatibility check on the computer acting as the host as part of the setup to ensure that it has enough compute to meet the needs of the workflow.

NDI Remote

The third application introduced in NDI 5.0 is NDI Remote, which aims to simplify the integration of remote contributors into a live production setup. It generates an actionable link via email or messaging to enable recipients to receive video and audio feeds from remote devices, whether that is a PTZ camera or a smartphone. It supports up to eight simultaneous remote connections as well as providing tools for managing the video feed, such as muting the microphone, switching camera views, and adjusting bandwidth settings.

Conclusion

NDI is easy to set up, its user-friendly tools make it easy to operate and its increasingly widespread adoption has made it an attractive way to integrate distributed and remote IP connectivity into broadcast workflows. NDI clearly presents some advantages, particularly when it comes to simplifying workflows and reducing cabling, but there are wider considerations for broadcasters looking to integrate NDI into live environments.

Perhaps the biggest barrier is still that NDI is not a formal standard, and its lack of a standardized framework can lead to implementation challenges if third party vendors choose not to support backwards compatibility. And although NDI simplifies the connection of devices over IP networks – and it absolutely does – managing a large number of IP streams in complex, distributed broadcast setups is no walk in the park, and far more broadcast vendors are on the same SMPTE and NMOS roadmaps than NDI.

While NDI is increasingly used for live contribution feeds in things like news broadcasting, to date The Broadcast Bridge is unaware any instances where it has been adopted as core infrastructure for tier one programming.

But time will tell, and developments like NDI Audio, which presents an extremely elegant way to deliver multiple audio channels in a deterministic workflow and at fixed low latencies, only presents more opportunities for the company to develop.