Weird thing is that the recorded file has your screen resolution even while the window was smaller. Then when you use the Region Recording Hotkey it shows the overlay where you chose the Red Alert 2 application and it starts recording.
Enable Show Overlay in the main settings tab. There enable the Region Recording Hotkey and Borderless Region Capture. Run the game in windowed mode ( alt+enter) because ReLive seems to be unable to record in 65k color depth (or because it's DirectDraw).
In the Radeon drivers settings enable the ReLive.
