Set to 2 Meg or less
GOP (Group of Pictures) is a group of frames (consisting of I-frames, B-Frames and P-Frames). H264 and H265).
I-frames are bigger than P-frames, therefore larger gaps between I-frames can optimize the bandwidth consumption and storage space.
Setting a GOP to 1 would mean only I-frames.
GOP must be used with Variable Bit Rate (VBR), and not Constant Bit Rate (CBR).
Remember that when setting up a camera for analytics, to zoom in as much as possible on the object / reason for the analysis. Extra scene view is wasting time and processing power.