In the new H.264/AVC standard, when entropy coding mode is set to zero, residual block data is coded using a context adaptive variable length coding (CAVLC) scheme. The first VLC, coeff_token, encodes both the total number of nonzero coefficients and the number of trailing ones. There are four choices of look-up table to use for encoding coeff_token for a 4times4 block. In this paper we discuss the results of assigning shorter codes to more probable pairs (Num-coeff, T1s) adaptively and vice versa. There are big gaps between the probability lines of three pairs ( (0,0),(1,1) and (2,2) ), so adaptive probability updating can't give better results. The probability lines of other pairs intersect each other and adaptive probability updating gives better results, but the probability (ap10%) of these pairs is very small