NDI graphics: overlays that travel over the network
NDI carries video, audio and alpha over ordinary IP networks. For graphics, that means a title can be produced on one machine and keyed on another — a vision mixer, a switcher, another building. Here is when that matters and when a browser source is the simpler answer.
What NDI is
NDI (Network Device Interface) is a protocol for sending low-latency video over a normal gigabit network. Sources announce themselves, receivers discover them by name, and the picture arrives with a handful of frames of delay instead of the seconds a streaming protocol would add.
For graphics, the important part is that NDI can carry an alpha channel. A titles machine can therefore publish just the graphics, transparent, and let the switcher composite them over the programme.
Key and fill, in one stream
Traditional broadcast keying sends two signals: the fill (the coloured pixels) and the key (a greyscale mask saying where they are opaque). Two SDI cables, two inputs on the mixer.
An NDI source with an alpha channel carries both in one stream. A mixer that understands NDI alpha keys it directly; one that does not can usually be fed a fill output and a key output derived from the same source.
NDI or a browser source?
- Use a browser source when your programme is assembled in OBS, vMix or Streamlabs on the same machine. It is simpler, costs no bandwidth and adds no latency.
- Use NDI when the graphics have to leave the machine: a hardware or software vision mixer, a separate gallery PC, a Ross or Vizrt chain, or a second operator position.
- Budget the bandwidth. 1080p with alpha is real traffic — plan a dedicated gigabit path and do not share it with the internet uplink.
- Mind the clock. NDI is low latency, not zero latency; a mixer will still need a frame or two of delay compensation.
Where LowerThird Software stands
Today the output is an HTML5 browser source, which is what OBS, vMix and Streamlabs want anyway, and it is what the great majority of streams need.
NDI output with alpha is the next major item on the roadmap, aimed squarely at studios that want to feed a vision mixer instead of an encoder. It is a second carrier for the same graphics engine: the same panel, the same templates, the same scene state, published as a network source as well as a web page. How the HTML5 path works today →
Start with the browser source Everything on air today runs through one transparent page. Ask for an early-access build and tell us what your studio needs from NDI.
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