I managed to get Unreal Engine and the offworldlive plugin working.
I believe there are a couple of problems.
First the Unreal plugin is producing a sender but not recording the texture format. You can confirm that by using the Spout demo sender and RH click to bring up the sender selection dialog, then click on the texture format button. It should show the sender details with Format = 0. The Unreal plugin is probably not filling this sender format field.
The DirectX example receiver will not work either
The other problem is the actual texture format produced by Unreal engine. I detect this as 16 bit float rgba, but SpoutCam uses 8 bit rgb pixels and normally there is a conversion between 8 bit bgra and 8 bit rgb.
It might be possible to create a function to convert from rgba floats to rgb, but it would be easier if the output pixel format of Unreal Engine could be changed. Can this be done by the user? If so, choose bgra format.
The plugin still won’t work, but the example directx receiver might.