Motion detection from Amcrest NVR


I have 4 Amcrest cameras connected to an NVR and I’m trying to get the motion detection into Home Assistant. I tried to use the Amcrest component but since the cameras are connected to the NVR’s switch I only have one IP and consequently I can only stream the first camera and the motion sensor doesn’t work.
Now I’m using the ffmpeg camera platform and I have the 4 rtsp streams working, but I can’t manage to make the ffmpeg motion component to work.
Someone with a similar setup managed to get motion detection from an NVR?