Smoothing: Adjusting the size of I frame. In video streams, I frame>P frame>B frame. By decreasing the smoothing index, I frame size is increased and the image is clearer. While increasing the smoothing index, the size of I frame would be decreased and would get close to P/B frame size. And the image looks smoother.
The smoothing index can be used to adjust the stream bandwidth. The adjustable range is 0-100 and the default value is 50.