now i've tested several Options.
I set global Videomode to CEA 4 HDMI - no schange
in the mupen64 config i changed the Resolution to 1440x1080. It's 4:3 but the screen is not centered, it's on the left screen side.
The Options are correctly set to force 4:3 But with the 1920x1080 Resolution it's still streched.
When i use the libreto core it's centered and 4:3 but this core is significant slower.
So what can i do now?