I've got BI 4.0 running on several Windows 8.1 systems with very little drama. The only real issue I ran into at install time was the failure requiring the VC++ redistributable packages, but the README for
Blue Iris 4 indicates what to do in that case.
My problem is with displaying the image from a couple of HD cameras, it's simply a green screen with no image. I've got wireless low def cameras and USB cameras with no problem. But I have 2 Logitech HD Pro Webcam C920 USB cameras that absolutely refuse to display. I tried all of the image format sizes possible and nothing helps. If I use 160x120 at 7.5 frames per sec it show about 10% of the image.
When I use the same exact cameras on the latest BI 3 version at 864x480 and 7.5 frames per sec I get a perfect picture.
For now I switched my website feeder back to BI3.
Incidentally, it's pretty simple to switch back and forth between BI3 and BI4 on the same machine, you just have to pay attention and use the startup from the correct directory.