In You Tube now (May 2019) it's called "Stream (Beta)" and I managed to figure it out.
In the hope that it may help any other beginners, like me, I have written out basic instructions for using an NDI stream to feed out to Zoom and You Tube from a Tricaster 410.
Here it is:
How to stream from Tricaster
1 On TRICASTER
In Program click the “NETWORK” box (blue means selected)
Alongside that, where it says Follow 1, right click and select “Deinterlaced”
Ensure that DDR1 is selected as the Program output and that the output is showing above Program.
2 On any PC on the Network
To stream to Zoom
Open OBS
Under Source, Select NDI Output
Right Click Properties
Ensure Source Name selected from the dropdown is TRICASTER and press OK
The NDI output (from Program) will appear in a red window
Open Zoom and follow the instructions there and the stream will appear
To stream to You Tube
Open OBS and under Source, Select NDI Output
Right Click Properties and ensure Source Name selected from the dropdown is TRICASTER and press OK
The NDI output (from Program) will appear in a red window
Go to You Tube and “Go Live” for video and select Stream (Beta)
Fill in the details of the stream and obtain a Keycode
In OPS, Under Settings, select Stream
Select You Tube
Paste the code into the box and click Apply/OK
Select Start Stream
The stream Preview will take a few seconds to appear on You Tube
Press Go Live and stream will commence.
