Video transport: SDI, HDMI, NDI, SRT and fibre.

Your cameras are spread around the venue, the switcher is in a corner and the video technician is twenty metres from the stage. The decision determining the setup is not which camera you buy, but how you carry the signal from each point to the production switcher and then return it to the monitors. Choosing transport badly forces recabling, adds latency and turns a small fault into a lost signal mid-set.

Each part of a production has different conditions: connecting two devices in the same rack is not the same as linking two halls or receiving a remote camera over the internet. This guide organises the options by what matters live—distance, reliability, latency and ease of diagnosis—and explains where each technology ends and which converter is needed at the boundary.

HDMI and SDI: the basis of live signals

HDMI is everywhere and inexpensive, but was not designed for live setups. Its connector does not lock, comes loose with a tug and does not handle repeated setups and teardowns well. In practice, passive HDMI rarely exceeds a few metres reliably; beyond that you need an active cable, an extender or another technology. Add HDCP: if a source demands it and the destination does not negotiate it, the picture disappears without further explanation.

SDI is the opposite: coaxial cable with a locking BNC connector, immune to HDCP and designed for medium distances. A single cable carries uncompressed video and, in many formats, embedded audio too, simplifying cabling. Within a venue, SDI is the default option for camera-to-switcher and switcher-to-monitor runs because diagnosis is simple: there is a signal or there is not, and a local monitor confirms it in seconds.

The boundary between them is the converter: an HDMI-to-SDI converter brings a consumer camera into a professional chain, while an SDI-to-HDMI converter serves the inexpensive monitor at the graphics station. Every conversion adds a power point and a possible failure, so concentrate them in the rack rather than scattering them around the venue.

SDI: from 3G-SDI to 12G-SDI and optical

SDI is not a single standard. 3G-SDI covers 1080p at 50 or 60 frames per second, 6G-SDI reaches 2160p30 and 12G-SDI allows 2160p50 or 60 over a single coaxial cable. The rule to remember is that a higher data rate means a shorter achievable distance: a cable carrying 3G-SDI without problems over tens of metres may fail with 12G-SDI on the same run. If the setup will grow to UHD, check cable and connectors beforehand, rather than on show day.

When copper cannot reach, you enter optical territory. Optical modules (SFP) convert the electrical signal into light and allow runs of hundreds of metres or kilometres without repeaters, with total immunity to electromagnetic interference and no ground loops between buildings. A properly laid fibre run is also the most resistant to dimmer and power noise. The price is care: minimum bend radii, clean connectors and always a spare patch cable.

IP video: NDI, NDI HX and RTMP

IP video changes the paradigm: instead of one cable per signal, everything travels over Ethernet. NDI is the protocol that has popularised this way of working in productions with limited budgets. It discovers network sources automatically, carries compressed video with low latency and allows a new camera to be added without running a new cable, provided the switch and network support it. The price is dependence on that network’s condition: a poorly sized LAN ruins the picture.

NDI HX is the low-bandwidth variant. It uses more aggressive codecs to fit into Gigabit networks and modest equipment, in exchange for some extra latency and less grading headroom. It is a reasonable option when sharing the network with other services or when the number of sources grows. RTMP, by contrast, is the classic delivery protocol: it runs over TCP, handles unstable links poorly and adds high latency, but is what streaming platforms expect for publishing the programme.

SRT and RIST for unstable links

SRT (Secure Reliable Transport) was created for reliable video contribution over the internet. It operates over UDP, retransmits lost packets and allows a configurable latency buffer: if the link is poor, increase it and gain stability in exchange for delay. It also encrypts the stream, which matters when the signal leaves the venue.

RIST (Reliable Internet Stream Transport) pursues the same objective through an open forum, with packet recovery and the ability to multiplex several streams within one link. In practice, SRT and RIST are interchangeable in many setups; what matters is that both are intended for contribution rather than final delivery. A properly sized contribution link usually ends at an encoder that publishes to the platform over RTMP.

Extenders, converters and distribution

Extenders carry a signal further than its interface permits on its own: there are HDMI extenders over twisted pair or fibre, and SDI extenders for long runs. They are usually transparent to the signal, but need power at both ends and add another point to check when something fails.

Distribution is the other side of the problem: one signal must reach several destinations. An active distribution amplifier (DA) replicates the input across several outputs while maintaining level; daisy-chaining monitors one by one degrades the signal and eventually fails at the last one in the chain. At every boundary between technologies, converters are needed: HDMI to SDI, SDI to fibre, fibre to IP. Fewer intermediate converters mean less accumulated latency and fewer possible failures.

Choosing transport according to distance

The following table summarises indicative maximum distances for each option and the part of the chain it best suits. Use it as a starting point rather than an absolute rule: cable quality, temperature and connector condition move the result considerably.

The practical rule works by section. Inside the rack, HDMI is enough. Between positions in the same venue, copper SDI; if the run crosses halls or passes beside power, fibre is better. For production spread over a network, NDI or NDI HX simplifies cabling. To send a signal outside the venue, use SRT or RIST over the internet, with a secondary line whenever the broadcast is critical. If you only need to publish, RTMP is more than adequate despite adding seconds of delay.

Routing matrices and signal routing

As sources and destinations multiply, point-to-point becomes unmanageable. That is where routing matrices come in: a router that switches any input to any output without rearranging cables. A classic SDI matrix handles a venue with several screens and monitors; IP matrices do the same with NDI streams and grow without changing cables.

Either way, label inputs and outputs with names rather than numbers, and document the signal map before setup. A poorly documented matrix is worse than no matrix: under pressure, nobody remembers which input belongs to the booth camera.

Common diagnostic mistakes

Transport faults repeat: a cheap HDMI cable coming loose, dirty fibre patch cables, unpowered converters, a saturated switch because the network is shared with other things, or accepting a format because it worked with another cable. Before the show, test every section at the final resolution rather than a test resolution.

Measure and note the actual run length, cable type, signal rate, expected latency and what you will do if that section fails. Having a spare converter and a few extra metres of fibre solves more live productions than any advanced setting.

Next step

With transport handled, the next problem is what you do with the signals at the switcher. Continue with Switching and vision mixing: cut, mix, keyers and macros to work on transitions, layers and macros, and revisit Architecture of a live multicamera production if you still need to organise the complete signal chain.