Network Device Interface

Network Device Interface (NDI®) is a royalty free standard developed by NewTek to enable video-compatible products to communicate, deliver, and receive broadcast quality video in a high quality, low latency manner that is frame-accurate and suitable for switching in a live production environment.

Technology

NDI was developed by NewTek, and is available to anyone with a royalty-free license. NewTek has an SDK available for Windows, Linux and macOS.^[1] NDI has also been ported to iOS, Android, Raspberry Pi, and FPGA.^[2][3]

NDI is designed to run over existing Gigabit networks,^[4] with the NDI codec^[5] expected to deliver 1080i HD video at VBR data rates typically around 100 Mbit/s.^[6]

NDI uses the mDNS (Bonjour / Zeroconf) discovery mechanism to advertise sources on a local area network, such that NDI receiving devices can automatically discover and offer those sources. Sources are created using an arbitrarily selected TCP port from a range of ports on the NDI send host. When a source is requested a TCP connection is established on the appropriate port with the NDI receiver connecting to the NDI sender. NDI 3.x has options to use UDP Multicast or Unicast with FEC(Forward_error_correction) instead of TCP, and can load balance streams across multiple Gigabit NICs without link aggregation.

NDI carries video, multichannel uncompressed audio and metadata. Metadata messages can be sent in both directions allowing the sender and receiver to message one another over the connection with arbitrary metadata in XML form.^[7] This directional metadata system allows for functionality such as active tally information fed back to sources to understand that they are on-air (program / preview). NDI also allows senders to determine the number of connected receivers, so they can skip unnecessary processing and network bandwidth utilisation when there are no NDI receiver clients connected.

Comparison with other protocols

Other IP Video protocols emerging for use in professional video production (rather than IP Video used for distribution to end users) include SMPTE 2022, SMPTE2110, ASPEN (which appears to have been largely superseded by SMPTE2110) and Sony NMI. There are clear differences in the technology used by these protocols.

*The TICO codec can be used to compress UHD by 4:1 so an encoded stream can be carried along a SMPTE_2022-6 channel at the same uncompressed bandwidth as HD.^[15] SMPTE 2110 with TR-03 also offers the potential to use TICO.^[16] This requires a proprietary encoder and decoder which are generally implemented as silicon on each end. * * NDI v1.0 was pure TCP. Later versions included options for UDP Unicast and Multicast as appropriate and FEC. NDI HX is generally UDP but uses TCP control commands.

History

NDI was publicly revealed by NewTek on 8 September 2015 and was demonstrated at the IBC broadcast exhibition in Amsterdam that week.^[17] The first device shown using NDI was the NewTek TriCaster which delivered an NDI feed from each of its SDI inputs as well as 4 output feeds from its vision mixer. TriCaster could also receive up to 2 NDI sources from other devices (increased to 12 in later releases and up to 44 in NewTek's IP Series ).^[18]

NDI devices from other vendors followed during 2016. The first 3rd party products came from Gallery Sienna and included an NDI signal generator for macOS, a desktop scan converter for macOS and the NDICam camera app for iPhone which delivers a native NDI stream from iOS devices.^[19][20].

NewTek had previously created a predecessor of NDI called AirSend to get video from external devices into their TriCaster products. AirSend had been implemented by a number of CG manufacturers including VizRT and Chyron. In order to quickly bring these products into the NDI space, NewTek created a new driver to replace the existing AirSend driver, which could be installed on these existing AirSend compatible devices, instantly converting them to NDI compatible devices with no change required by the original CG vendors.^[21]

Another early adopter of NDI was VMix, a Windows-based vision mixer which offers NDI inputs and outputs.^[22] A significant increase in the NDI installed base came when live streaming application XSplit added support for NDI.^[23]

Later in 2016, NewTek delivered NDI 2.0 which added features including support for service discovery across subnets. In the first half of 2017, BirdDog began demonstrating and shipping BirdDog Studio NDI - a PoE powered portable FPGA based NDI encoder with HDMI and SDI inputs with Tally, supporting up to 1080p60 video resolutions.^[3] On 12th July 2017 NewTek announced NDI 3.0 which added multicast, NDI/HX and other new features, introducing support for specific PTZ Cameras with H.264 chipsets and updated firmware. ^[24]

In April 2018 at the NAB Show, Microsoft announced they had added NDI support to Skype for Content Creators.^[25] Other announcements at NAB2018 included NDI 3.5, and new NDI support from vendors including EVS^[26] and Avid.^[27]

Use in Wifi and Wide Area Networks

NDI was designed to work on good quality gigabit local area networks using TCP and Bonjour (mDNS) technologies. In order to work across subnets which don't pass mDNS, NDI supports a mechanism known as NDI Access which allows manual entry of the IP address of machines on other subnet which may be running NDI sources.

Some NDI adopters have run the protocol across medium distance Fibre connections up to 15 km, although NDI's use of the TCP protocol make it less suitable for longer distance, high latency connections due to factors such as Bandwidth Delay Product and TCP packet loss recovery.^[28] The NDI 3.5 libraries now default to a UDP transfer method with forward error correction that removes the latency requirements that are inherent with TCP connections. NDI|HX uses a lower data rate making it easier to use in bandwidth limited connections.^[29]

To provide an extension of NDI to wide area networks, tools have been developed including the Sienna Cloud for NDI^[30] protocol which uses node gateways in each LAN to bridge NDI sources across continents.^[31] In July 2017, USSSA (United States Speciality Sports Association) successfully made the first truly wide area network NDI sports coverage using Cloud for NDI with 5 cameras backhauled across the public internet from a stadium, to 200 miles away into an NDI based production gallery. ^[32]

CPU architecture support

NDI, when running on x86 architectures, requires CPU's that include the SSSE3 (Supplemental Streaming SIMD Extensions 3) instruction set. Most Intel CPU designs starting in 2006 have this instruction set, AMD added support starting in 2011.

While not a requirement, NDI will take advantage of AVX (Advanced Vector Extensions) and AVX2 instructions sets for additional performance. While NDI itself doesn't require these instructions, applications might.

NDI can run on 32-bit or 64-bit CPU architectures, although performance is increased when using 64-bit, and 32-bit support may not be available in future versions of the macOS and iOS NDI Libraries.

NDI is available for ARM based systems with encode support, but not decode.

NDI HX Devices are typically send-only and based on proprietary platforms with hardware H.264 encoder chips. Examples are NDI HX PTZ Cameras, and the NDI Connect Spark SDI to NDI HX box. The NDI Stream itself is formed at the stream consumption end via the platform specific NDI HX driver, presenting the same uncompressed data to the application software consuming the NDI source regardless of original HX source hardware and compression.

NewTek, Birddog and Magewell have all developed FPGA implementations of NDI. In April 2018 NewTek announced the Connect Spark Pro which will be their first FPGA based NDI product.

Adoption

The NDI Protocol has been widely adopted by a diverse variety of software and hardware vendors. The table below includes a partial list of products known to support the NDI Protocol

References