In DC analysis, both (C1,C2) will be open circuited, thus the current passes through (Rc) will be divided into (Rb) and the transistor.
In AC analysis, the capacitors will be shout circuited, thus you can place the AC-model and decompose (Rb) by miller theorem.
The Voltage gain(Av) = -{Gm(Ro||RL||Rc||Rmi)}/{(Rmi||Rpi)/(Rmi||Rpi)+Rs}
Where: Rmi => miller input resistance.
Rmo => miller output resistance.
Ro => transistor output resistance.
Rpi => transistor resistance between base and emitter.
Hope this helps