Just to be clear, wasn't trying to open the file when it was open, I should have said. I'd set recordings to 1hr and they are around 1.6Gb but BI can't open them and can't open them in other apps.
I actually switched from bvr cos I was getting insane cpu usage. I'll keep trying different...
I am new to blueiris and used the demo the customise the setup and test recordings, and evrerything seemed to work OK. Got the cameras mounted, they are 4k 8MP Hikvisions, using H265+ (edit to add now have paid full version)
I have motion detection to take jpeg snapshots every 0.5 sec and...