Hi,
This depends very much on the resolution of the cameras. A higher resolution demands a lot from the CPU. Our experience is that using Intel’s integrated graphics with DXVA2 really do not reduce the cpu load that can be measured.
What is the resolution of the camera? Do you use mjpeg or h.264 from the camera? In general mjpeg use more bandwidth on the LAN, but less cpu power compared to h.264. Is the fps limited from the camera?
If you need a total of 16 cams I would recommend an i7 processor with the actual settings of NCS and of the cams. The i5-7400 have 4 cores, but no hyper-threading so it have only 4 threads. The encoding/decoding process works best with many threads.
Read also this post Compression Causes recording to fail for very high resolution cameras - tests and results
-Henrik