I saw your datasheet states "1080p100 H.264 encode/decode/transcode" What the 100 stands for?
This refers to 100 fps or equivalent. The microNVR1500 or the HiveCAM 1500 are both capable of 1080p100 encode or decode in the GPU. So you could have 3 streams at 30fps, 6 streams at 15fps, 12 streams at 7fps, etc. If you run at lower resolution you can have more cameras too. This is a generic measurement of video processing capability.