Ok, the test was successfull ...
I made some changes:
1.) changed from H.264 to MJPEG Video Format
2.) changed the focus point to a nearer object
3.) I removed two obstacles, which stood left and right of the camera (to hide it a bit)
I think, it was no.3 ... why?
Cause may be the IR-lights were reflecting the IRs?
I am not sure...