First method - the simplest, I calculate the file size divided by duration (in seconds).
This is in fact consistent with second method: information given by MPC-HC (Media Player Classic HomeCinema) by going to File->Properties, and then on Details tab, as well as on Mediainfo tab (very detailed stuff).
Third, I check with VLC by chosing Tools->Codec information, and then Statistics tab (please note the file needs to be actually playing - cannot be paused).
All these methods give same/similar result - of course to some average numbers. It is not always exactly precisely strict 5Mbps, but running around that number.
That value of 3.5…5Mbps was for low resolution USB webcam 320x240. The value of around 15Mbps is for my 720p source from Escam Q6 camera (here I also record audio stream at 40kbps).
Not sure if that’s important but for CPU encoded files, I can see in MPC-HC that there is “x264 core” as the “writing library”. But for files with “Intel” encoding engine, there is no information about writing library. So it seems it is in fact encoded differently - the encoding engine switch in Netcam settings somehow works, but cannot set CRF quality.