You can use the Spout plugin for OBS Studio to receive Spout video inputs from any Spout enabled program:

1. At the bottom of the Sources window click the + icon which will show you a list of all possible input sources. From this list, select Spout 2 Capture.
2. This will open a window called Create/Select Source. Ensure that Create new is selected here and press OK. You can also rename the Source if you like. 
3. Double-click the Source to open its Properties:
   1. Select your Spout Sender from the available list. These will be named as in the program you are sending your Spout feed from.
   2. Composite mode is set to Opaque unless you want an alpha output.
   3. Pull time for new sender is left as the default option.
   4. Click OK to return to the main OBS page. 
4. Resize Output:
   1. Right click the image/ video inside the main window
   2. From the menu list that appears, select Resize Output (source size).
   3. In the window that appears called Resize Output (source size) select Yes (to the question Do you want to continue.
      
5.  Your output window should now be the same as your Source size.