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Sienna NDI Insider Know-How Series

with Mark Gilbert, CTO Gallery SIENNA



Part 1 - What is NDI HX 2 ?



Many of you will be familiar with NDI HX, the protocol used by many of the first generation baseband converters and PTZ Cameras.  NDI HX is a hybrid protocol designed to bridge between traditional IP Streams like RTSP/RTP and the easy-to-integrate NDI world - whilst there are changes to the device firmware, most of the work to construct NDI HX1 is done in the receiving device HX drivers.  NDI HX typically carries H.264 video and AAC audio from devices with hardware based H.264 encoders like PTZ Cameras designed for the broader non-NDI market.  Discovery of HX1 devices is different to regular NDI and can introduce different networking challenges. HX1 works well, and is a good foundation for the next generation HX2 to build upon.


So what is NDI HX2 ?

Well - HX2 is the next generation high efficiency NDI protocol - it also uses H.264 - although it can also use H.265(HEVC) - and the main difference compared to HX (1) is that HX2 is truly a native NDI stream - all the way from the source device to the destination. This means it is a somewhat 'cleaner' implementation than HX1 and can potentially provide a more reliable, lower latency and more flexible connection which shares all the usual features of NDI like 3 different options for discovery (mDNS, NDI Access polling and NDI 4 Discovery server), the ability to carry arbitrary NDI Metadata and the same control over low level network transport (TCP, UDP, Multicast and mTCP).

With higher bit rates and options for HEVC, NDI HX2 can offer similar visual quality to full NDI with WIFI and even WAN compatible bandwidth. Latency depends very much on the codec implementation in sending and receiving devices, but can theoretically be as low as a couple of frames.


Who is doing NDI HX2 ?

Decoding of NDI HX2 is built into the NDI4 drivers for Windows, macOS and Linux, and so most software using NDI4 will be able to decode HX2 without any changes. The first NDI HX2 sending device was the second generation NewTek NDI Camera for iOS. Since then other vendors are working on HX2 devices, and we expect to see HX2 based hardware in the near future.

Other HX2 compatible systems include Sienna's NDI Monitor for iPhones/iPads and the Sienna's new NDI Monitor TV for AppleTV 4K. Another important addition to the HX2 landscape is the NDI HX2 distribution amplifier module in the Sienna NDI Processing Engine. This allows you to take as many full NDI streams as you like and create NDI HX2 versions, which have selectable bit rate, and can be individually configured as multicast to provide powerful new options for large site distribution to signage or other groups of monitors using the AppleTV 4k as a decoder. We have even used the HX2 distribution amplifier for easy downlink of NDI Streams from production in the cloud, direct to Apple TV4k on the ground, across a transatlantic public internet connection. This is truly native wide area networking for NDI with no intermediate conversions adding latency or complication.


Sienna's NDI core technologies support HX2 alongside all other flavours of NDI. Having the choice of bandwidth allows systems integrators to create more flexible workflows, including wide area infrastructure.  Please let us know if you have any follow up questions, or you want to dig into the Sienna NDI Infrastructure product line and get on board with this unprecedented revolution in broadcast media infrastructure


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