On MPEG-2 decoding of noisy input data

Due to the high compression ratio of the MPEG-2 video compression scheme, the effect of corrupted bits during transmission over a noisy channel is tremendously increased compared to uncompressed transmission. Moreover, due to the hierarchical structure of the MPEG-2 bitstream, the damage caused by channel noise depends on the position of the corrupted bit in the bitstream. Analysis shows that the most important (or most sensitive) bits are those of the MPEG-2 start codes. Loss of a start code usually causes the unrecoverable damage of an entire slice or even a whole sequence of pictures. An optimum detector for start codes is presented. In contrast to classical MPEG-2 decoders, this detector is based on the real-valued channel output (soft values), instead of already detected binary values (hard decisions). Performance analysis shows an SNR gain of about 6 dB compared to the classical hard decision detector.