In video communications over error introducing channels, error concealment techniques are widely applied in video decoder for good subjective images output. However, a damaged MB could be concealed only after it is detected as erroneous. Because of the poor performance of the traditional syntax based error detection schemes, the error concealments thereafter show bad results. Our previous work explored the potential of transmission error detection by fragile watermarking. In this paper, a synchronous fragile watermark based transmission error detection scheme for hybrid decoder is proposed. By watermarking, we enforce a synchronization signal like correlation on Q-DCT coefficients. Thus the decoder could use this pre-forced information for detecting errors. The simulation results show that the erroneous Q-DCT coefficients detection capabilities are largely improved compared to syntax-based scheme.