NDI
A protocol for moving video, audio and control between cameras, computers and switchers over the local network, without capture cards or video cables.
NDI (Network Device Interface) moves production-quality video and audio between devices on the same local network. It is how you build a live show: cameras, shared screens and graphics reach the switcher over the network. It is not how the show reaches the audience: for that the switcher sends the signal to the platform over RTMP.
What is NDI?
NDI is a protocol NewTek launched in 2015, now part of the Vizrt group. It turns any device on the network into a video source or destination: a camera, a presenter's computer or the output of a switcher. Sources are discovered automatically on the local network, with no addresses to type in.
In practice it replaces capture cards and long SDI or HDMI runs. One network cable carries video, audio, PTZ camera control and a return feed.
How it works
NDI cameras, computers running NDI Tools or mobile apps publish their signal on the local network.
The switcher sees available sources by name and adds them as inputs.
vMix, OBS with the DistroAV plugin or a TriCaster combines cameras, screens and graphics into the programme.
The switcher sends the programme to the live platform over RTMPRTMPThe protocol encoders such as OBS and vMix use to send a live signal to the platform. Viewers then watch over HLS.Open definition →, and the platform delivers it to viewers.
Full NDI and NDI HX
| Full NDI | NDI HX | |
|---|---|---|
| Compression | Light, visually near-lossless | H.264 or H.265 |
| Bandwidth per 1080p source | In the order of 100 Mbps or more | A few Mbps |
| Latency | Minimal | Somewhat higher |
| Typical use | Studio on a 1 Gbps wired network | PTZ cameras, phones, Wi-Fi |
NDI vs RTMP vs SRT vs WebRTC
| Protocol | What it is for | Network |
|---|---|---|
| NDI | Moving signals between production devices | Local network |
| RTMPRTMPThe protocol encoders such as OBS and vMix use to send a live signal to the platform. Viewers then watch over HLS.Open definition → | Sending the live signal from the encoder to the platform | Internet |
| SRT | Carrying video over unstable networks with error recovery | Internet |
| WebRTC | Real-time video in the browser, such as video calls | Internet |
They do not compete: one live show can use NDI inside the studio and RTMP to reach the platform.
Further reading
- NDI — the official site of the protocol and NDI Tools.
- Kinescope: connecting the stream — RTMP servers and supported encoders.
