In this paper, residual redundancy in compressed videos is exploited to alleviate transmission errors using joint source channel arithmetic decoding. A new method is proposed to estimate a priori probability in MAP metric of H.264 intra modes decoder. The decoder generates a decoding tree using a breadth first search algorithm. An introduced statistical model is then implemented stage by stage over the decoding tree. In this model, a priori PMF of intra block modes in a macroblock is estimated from the intra block modes seated in its spatially adjacent macroblocks previously generated up to the current stage of the decoding tree. The estimated PMFs are categorized as either reliable or unreliable based on their local entropies. In the unreliable case, the decoder assumes uniform PMF and switch to ML metric instead. The simulation results show the proposed method reduces the error rate 1% to 13% at various SNRs compared to the ML.