Defined zone shows as slightly shifted when I test run a video clip

[edittech12]

Hi all, I've only recently setup Blue Iris 5 for the first time with my 3 Dahua IP cams and have been tinkering and optimising it.

I've noticed something strange which I can't quite figure out. I define a zone for one of my cameras using a live preview image where I paint or clear the bits of the picture I want covered or uncovered by the motion zone.

When I then go to view a clip (recorded after defining the zones and no changes to the camera zoom) and enable the 'Test run video through motion detector' option, areas which are not in the zone are blacked out, which is fine, but from that I can see that on the clip, the blacked out areas are shifted to the right a bit so it's not quite what I setup in the zone settings. I had defined the zone to exclude a window and sliding door to reduce false triggers but because the zone has somehow shifted, the camera is picking up some motion through my window and door.

There is another issue I've got which I think might have the same root cause. I've been testing using overlays provided by Blue Iris tools and in the preview image I position the overlay text in the top right corner of the camera image but once I save and view my camera's live feed, the overlay text appears more to the left and not in the corner where I put it.

The only possible cause I can think of is something to do with the main stream and substream. Is the preview image (for motion zones and overlays) using an image from the substream image whereas when watching clips back and reviewing the overlay on the live feed I'm seeing the main stream? So the configuration is not being done on the same image I'm eventually seeing?

Any insight much appreciated.