In short: Use SDI for a cabled run of up to about 100 metres at HD, NDI for sources that share a gigabit network, and HDMI for short, simple runs. Full-bandwidth NDI needs at least a gigabit network, while NDI HX needs far less bandwidth. Every link adds some delay, so test the whole chain with a test file before the show.
Three connections cover most live jobs, and each one suits a different problem. SDI is a cable from one device to another. HDMI is a short link between two devices. NDI sends video over an ordinary network. The right choice depends on how far the signal has to travel, how many sources there are and what the equipment accepts.
How each one moves video
SDI travels over coaxial cable and is uncompressed. HD-SDI, defined by SMPTE 292M, runs at a nominal 1.485 Gbit/s. A typical limit for HD over coaxial is 100 metres, so treat that as a planning figure and check the cable's own specification. 3G-SDI runs at 2.970 Gbit/s on a single link.
NDI sends video over a local network using CAT5 or CAT6 cable, so one network can carry many sources. High bandwidth NDI keeps the picture close to full quality with light compression. NDI HX compresses harder to cut the bandwidth, and it adds some latency, which the vendor article describes as at most a frame or two.
HDMI is a consumer-style link that suits short runs between two devices, such as a camera and a monitor or a laptop and a small mixer. It is not the choice for a long run or a multi-camera show. Check the cable's own length rating before you buy it.
Bandwidth in practice
These are the NDI figures Epiphan quotes for 1080p.
| Format | High bandwidth NDI | NDI HX |
|---|---|---|
| 1080p30 | 100 Mbps | 8 Mbps |
| 1080p60 | 150 Mbps | 10.5 Mbps |
Full-bandwidth NDI needs a network with at least a gigabit of capacity, and the same article recommends leaving about 25% headroom for everything else on it.
Which to use when
- One camera, one cable, a run within the typical limit: SDI is the simplest path, and it does not depend on a network.
- Several sources across a building, on a network with spare capacity: NDI lets you send feeds to several places without a router for every output.
- A laptop or small device with only HDMI, on a short run: HDMI is fine. Keep the cable short.
- A mix of sources: use a mixer with the right inputs, then test the delay on each source.
Worked example
A stage has three cameras, and the vision mixer sits in a room across a corridor. Running three SDI cables and a router adds kit and cost. Instead, each camera sends a 1080p30 NDI feed at 100 Mbps, which makes 300 Mbps for the three. That fits a gigabit network with room to spare, and the headroom leaves capacity for the return feeds and the monitoring. Each feed is then tested with a test file to find its delay.
Common mistakes
- Assuming NDI works on any network. A busy Wi-Fi link or an unmanaged switch can drop frames.
- Using HDMI over a long run, then blaming the camera.
- Running NDI feeds on a link that is already close to full.
- Forgetting that each conversion and each link adds delay.
- Skipping the test. A latency and sync test file shows the total delay in frames.
For the bitrate side of a stream, use the streaming bitrate and bandwidth calculator. For the mixer side, see the vision mixing basics guide.
Sources
- Wikipedia, Serial digital interface, read 5 November 2026
- Epiphan, NDI and NDI HX network video production, read 5 November 2026
Related guides
- Vision mixing basics: ATEM and vMix
- Streaming bitrate and bandwidth calculator
- Live event run sheet template, and how to fill it
- Latency and sync test file: how to use it
- Free software for live production: OBS, Companion, CasparCG
- All guides and tools
The picture at the top of this page is an illustration, not a photograph of a client or a real job.
Questions we get asked
Is NDI better than SDI?
Neither is better in every case. NDI sends video over a network, while SDI sends uncompressed video down a coaxial cable. Choose by distance, the number of sources and what your kit accepts.
How much bandwidth does NDI need?
As quoted by Epiphan, full-bandwidth NDI at 1080p30 needs about 100 Mbps, and NDI HX needs about 8 Mbps. The same source recommends leaving about 25% headroom on the network.
What is the longest HD-SDI cable run?
Wikipedia's summary of the SMPTE standard gives a typical limit of 100 metres for HD over coaxial. Use that as a planning figure, and check the cable's own specification before you rely on it.
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