video matters
iTECH
For Richard Cadena, the road to authoring
books and magazine articles ran through
High End Systems and Martin, took a left
turn at designer, tech, and electrician, and
is still under construction.64 APRIL 2020 • WWW.LSIONLINE.COM
NDI takes the stage | By Richard Cadena
“NDI is a protocol that allows computers and other devices to share monitoring over
a data network with low latency.. .”
C
The first time I ever heard of Network Device Interface
(NDI) was probably about three years ago, but I never
really looked into it until very recently. If you’re familiar
with it, you’re probably thinking, “where have you been?”.
NDI is a protocol that allows computers and other devices to
share monitoring over a data network with low latency. The data
sent and received by an app running NDI can be video or
multi-channel audio, or it can be metadata. That allows it to also
be used for chromakeying using an embedded alpha channel,
as well as for proxy, control, tally, transporting custom
metadata, or precision time stamping. In terms of audio, it can
support up to 64 channels or more at 48kHz and 96kHz
sampling rates.
There are lots of products that accept an NDI input and there
are lots that send an NDI out, including computers, webcams,
media players, and media apps. There are also applications that
run on iOS, tvOS, Android, Raspberry Pi, and more. So you can,
for example, use it to take input from a smartphone for any
number of applications like live events or video conferencing.
The NDI protocol was developed by NewTek in 2015, and they
offer it royalty-free. There are NewTek software applications, as
well as third-party apps for monitoring, testing, and sending
data, and more, and they are available for Windows, MacOS,
and Linux. It’s a plug-and-play system whereby any device that
has the app is automatically discovered when it goes online. You
don’t have to worry about configuring the IP address or subnet
mask of the transmitter or receiver; as long as they are on the
same LAN, it will work. You can also use the NewTek NDI
Access Manager to connect devices across a subnet by
manually configuring IP addresses.
Sending monitor information over a network is a little trickier
than it might seem because Ethernet sends data in packets,
and video needs a certain amount of data to render each frame.
If the data for the complete frame is not delivered in a timely
manner, then it will create artefacts. NDI avoids this with some
trickery of its own so that it can deliver frame-accurate
monitoring and switching in real time.
Video can be a bandwidth hog, and the greater the resolution
and the higher the frame rate and bit depth, the more
bandwidth it needs. The bandwidth requirements are also
dependent on the content. It takes a lot more bandwidth to
transmit fast-moving images. To transport 1920x1080 video at 30
frames per second (FPS), NDI needs a dedicated bandwidth of
at least 125 megabits per second (Mbps) per stream. You can
transmit as many streams as your network can support.
If you have limited bandwidth you can use NDI HX, which
needs eight to 20Mbps of dedicated bandwidth per stream for
the same 1920x1080 video at 30 FPS. It uses H.264compression and will add one or two frames of latency.
Latency can be a deal-breaker in certain situations, but given
enough bandwidth, NDI can handle any resolution, aspect
ratio or frame rate.
In addition to a software development kit, NewTek also offers
free NDI tools to capture video from your computer or other
devices, to do remote monitoring, testing and control of video.
The NDI Studio Monitor is one of the apps in the toolbox that
simply mirrors a display across a network, and if you are
monitoring a PTZ camera with NDI support, you can also control
it remotely as well as configure NDI-enabled devices through
a web browser. It can run on any computer that can run
Windows 7 or better, or Mac OS X.
There is also an NDI Test Pattern app, but it only runs on
a Windows machine. This allows you to send one of several test
patterns and audio tones to test your network and Studio
Monitor app, and to calibrate your audio and video. The test
patterns include colour bars, colour fields, burst patterns,
colour ramps, cross hatches, IRE bars, IRE fields, and more.
The NDI Scan Converter allows you to capture your computer
desktop or any video source running on your computer and
send it across the network to a monitor. You can capture your
entire display or portions of it, as well as any combination of
windows, applications, players or webcams with very little taxingB The NDI protocol allows computers and other devices to video, multi-
channel audio, or metadata over a network