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Publish a canvas over NDI

When you publish a canvas over NDI (Network Device Interface), other NDI-compatible software on the same network, such as a vision mixer or a streaming encoder, can receive its picture and any audio you route to the canvas.

NDI output needs the Pro plan. See Plans and limits.

A stream is a destination you create, like a display. A canvas does not own a stream, so one canvas can send to several streams, and you can connect a stream to a different canvas while it stays the same source on the network.

Create the stream​

  1. Open Configuration.
  2. Under Venue, select Patch.
  3. Select + Add output.
  4. Under New, choose Network feed (NDI).
  5. In the Output panel, type a name in Name.

Receivers see this name together with this computer's name, so set it before other equipment starts using the feed. Center Screen is easier to pick out from another room than NDI output.

The stream does not publish yet, because no canvas sends to it.

Point a canvas at it​

  1. On Patch, find the canvas under Pictures.
  2. Drag from its port to the port of the stream under Network feeds.

A cable appears. To start the stream, switch Publish over NDI on in the NDI section of the Output panel. The stream's settings stay in its Output panel on Patch. You can also drag the stream into the Show column to make a new canvas for it. See Patch the show.

If the NDI runtime is not installed on this computer, the stream's row says so and shows no controls.

  1. Install the free NDI Runtime from ndi.video.
  2. Start ArenaDirector again.

Stop the stream​

There are two ways to stop a stream, with different results.

  • Stop the publication, but keep the connection. Switch Publish over NDI off in the Output panel of the stream, or select the cable and switch Connected off.
  • Disconnect the canvas. Select the cable and select Disconnect…. The stream stops but stays on Patch with its name and delay, ready to connect to a different canvas.

The only way to delete a stream's settings is to select the stream and then select Remove output….

Several streams from one canvas​

Create a second NDI output and connect the same canvas to it. Each stream is a separate source on the network with its own name, rate and latency offset, so a vision mixer and a streaming encoder can each receive a different frame rate from one board.

Rename the source​

Name is in the stream's Output panel on Patch, and it is the name a receiver's source list shows.

Renaming a live stream takes it off the network briefly; it then publishes again under the new name, and you have to reconnect the receivers. The NDI SDK does not let a source change its name after it is created. All other settings apply immediately.

Choose a rate​

Stream Rate is in the NDI section of the Output panel. It sets how often the stream sends a new frame over the network, and it applies to a canvas that has no screen.

If the canvas also sends to a screen, the stream uses that screen's refresh rate, and Stream Rate has no effect until you disconnect the screen.

To prevent stutter, set the rate your receiver software or encoder expects.

Route audio to it​

An NDI output carries audio as well as picture, so a bus can send directly to it.

  1. On Patch, find the bus under Sounds.
  2. Drag from its port to the port of the stream under Network feeds.

The stream is one stereo pair, so you do not select a device or a channel pair. See Set up a bus.

You can route a bus before the stream publishes; the audio starts when you switch Publish over NDI on.

Compensate for downstream delay​

Delay is in the stream's Output panel. It sets how much earlier than the room this stream gets its content.

Set it to the delay the receiver and the equipment after it add, as a positive number in milliseconds. Picture and sound both move by this amount, so the feed stays in sync at any setting.

The offset works the same way when the canvas also sends to a display. The display keeps its own timing while the stream gets content from a later point in time, so the display and the far end show the same thing at the same moment.

A negative number delays the stream instead, for a receiver that is ahead of the room. The group then keeps that many milliseconds of past pictures for the stream, which costs as many retained frames as a positive offset of the same size.

A group keeps at most sixteen frames before and after the current frame: about 250 ms at 60 fps and about 500 ms at 30 fps. The limit is the same for positive and negative settings.

If you set a larger offset than the group can keep, the stream uses the largest one that fits and the panel shows the part that does not apply. A typical receiver offset is 50 to 150 ms, well inside the limit.

What a trim costs the room

A sync group makes all its content early enough for its slowest member, so a 95 ms stream in House makes every screen in House respond to a button press about six frames later. To avoid this, move the stream to a second group, at the cost of the stream no longer being aligned with the room. See Add an output.

Monitor the stream​

The NDI section of the Output panel shows whether the stream is stable or recovering from a short problem, and counts repeated and dropped frames since publishing started.

If dropped frames keep climbing while the network is otherwise idle, a receiver or a network switch cannot keep up with the rate you selected.

See also​

NDI® is a registered trademark of Vizrt NDI AB.