So here I am a few weeks later thinking "Why did i have to put them back on H264 ?".
I went to my Dahua cam settings, and put them to H265 for the main and sub-stream. I could see the low res video in BI5, so manually triggered the camera to see what it would record. Nothing at all.
Reset to H264 and all OK. Reset to H265 and nothing recorded.
Now I've only tried it with one cam (so it could be that this cam needs a firmware update), but does anybody have any idea what is going on here ?
A search on the internet doesn't give any idea that it won't work with H265
