NDI

July 28, 2026 · View on GitHub

How to install and enable NDI for HydraSRT.

NDI® is a registered trademark of Vizrt NDI AB.

What HydraSRT ships, and what it does not

HydraSRT integrates NDI through the open-source GStreamer plugin gst-plugin-ndi (from gst-plugins-rs, MPL-2.0). That plugin is not the NDI implementation: it loads the proprietary NDI runtime (libndi) at run time.

HydraSRT does not include, bundle, or redistribute the NDI runtime. You install it yourself from ndi.video, and it stays subject to Vizrt's licence. Nothing here changes those terms. This page only explains how to point HydraSRT at a runtime you have installed.

NDI is off by default. With it off, NDI endpoints are rejected, the discovery coordinator is not started, and the API reports NDI_DISABLED.

Requirements

Component	Notes
GStreamer 1.x	Plus `-plugins-base` and `-plugins-good`/`-bad`.
`gst-plugin-ndi`	Built from `gst-plugins-rs`. Build with default features; the `advanced-sdk` feature stays off.
NDI runtime (`libndi.so.6`)	Proprietary. Obtain from ndi.video.
Avahi (`avahi-daemon`)	Only for mDNS discovery. `libndi` links `libavahi-client`; without a running daemon, automatic discovery is unavailable and you must use direct addresses or a Discovery Server.

1. Install the NDI runtime

Download the NDI SDK for your platform from ndi.video and run its installer. Then locate the runtime library for your architecture, for example:

NDI SDK for Linux/lib/x86_64-linux-gnu/libndi.so.6.3.2

Copy it to a directory of your choosing, and create the soname symlink:

sudo mkdir -p /opt/ndi
sudo cp "NDI SDK for Linux/lib/x86_64-linux-gnu/libndi.so.6.3.2" /opt/ndi/
sudo ln -sf libndi.so.6.3.2 /opt/ndi/libndi.so.6
sudo ln -sf libndi.so.6 /opt/ndi/libndi.so

The SDK ships one fully-versioned file per architecture (libndi.so.6.3.2) and no soname symlink. The loader looks for libndi.so.6, so without that link the runtime is not found even though the file is present.

Pick the directory matching the machine's architecture: the SDK also contains i686 and several ARM builds.

2. Verify GStreamer sees the plugin

gst-inspect-1.0 ndisrc

If this fails, the plugin is missing or not on GST_PLUGIN_PATH; HydraSRT will report NDI_PLUGIN_MISSING.

3. Configure HydraSRT

Two variables, both documented in envs.md:

NDI_FEATURE=true                 # enables NDI (default: false)
HYDRA_NDI_RUNTIME_DIR=/opt/ndi   # directory containing libndi.so.6

HYDRA_NDI_RUNTIME_DIR is passed to the native pipeline as NDI_RUNTIME_DIR_V6. Restart HydraSRT after setting them. make dev sets NDI_FEATURE=true already.

Discovery

By default NDI finds sources over mDNS, which requires a running avahi-daemon and working multicast on the network.

When multicast is unavailable

Cloud networks, many container setups and most CI runners do not pass multicast, so senders are never discovered. NDI's answer is the Discovery Server, which replaces multicast with unicast TCP. ndi-discovery-server ships with the SDK.

Run it, then point clients at it with a config file:

ndi-discovery-server &          # listens on :5959

// ~/.ndi/ndi-config.v1.json
{ "ndi": { "networks": { "ips": "", "discovery": "127.0.0.1" } } }

Two details that cost real debugging time:

The "ndi" wrapper is required. The flat form ({"networks": …}) is read without error and silently ignored.
libndi resolves this file from the account's home directory in the passwd database, not from $HOME. Overriding $HOME for the process has no effect. The file must exist for the account that runs HydraSRT, and both the sending and the receiving side need their own readable copy.

There is no environment variable for this on Linux; the config file is the only supported mechanism.

Referring to a source

A sender is advertised as MACHINE (Sender Name). When selecting a source by name, use that full advertised name; the bare sender name does not resolve.

Verifying

UI — the NDI health tab shows plugin, runtime, discovery and direct-address status.
API — GET /api/ndi/capabilities returns the same document.

Troubleshooting

Reported reason	Meaning	Fix
`NDI_DISABLED`	Feature flag is off.	Set `NDI_FEATURE=true` and restart.
`NDI_PLUGIN_MISSING`	`ndisrc`/`ndisink` not registered.	Install `gst-plugin-ndi`; check `GST_PLUGIN_PATH`.
`NDI_RUNTIME_MISSING`	`libndi` not loadable.	Check `HYDRA_NDI_RUNTIME_DIR` and the `libndi.so.6` symlink.
`NDI_RUNTIME_INCOMPATIBLE`	Runtime major version unsupported.	Install an NDI 6 runtime.
`NDI_AVAHI_UNAVAILABLE`	Avahi is not running.	Start `avahi-daemon`, or use direct addresses / a Discovery Server.
`NDI_DISCOVERY_UNAVAILABLE`	Discovery is not answering.	Check Avahi or the Discovery Server; direct addresses still work.
`NDI_HELPER_PENDING`	The discovery helper is still starting.	Wait a moment.
`NDI_HELPER_UNHEALTHY`	HydraSRT could not start its NDI helper.	Usually the runtime is missing or unloadable; verify steps 1-3.

Configuration with NDI unavailable can still be saved; only Test and Start are blocked until NDI becomes available.