There is an option on the iVMS4200 & keep in mind that if you are using a network during working hours (network traffic jam), the application may switch to substream due to the bad bandwidth, good luck
please check the image attached
you can say that Bit-rate is the amount of the picture details sent in 1 second
so the higher the bit-rate the higher quality you get
but you have to keep in mind that the High bit-rate consumes the line bandwidth