Constrained discrete-cosine-transform coefficients for better error detection in a corrupted MPEG-4 bitstreams

摘要

Error detection is added to a motion-picture-experts group (MPEG) decoder by checking each 8×8-pixel block for constraints. The constraints are added during compression by adjusting discrete cosine transform (DCT) coefficients in the block to meet a constraint. When the decoder determines that the constraint is not met by the DCT coefficients, an error is signaled for that block. The error can then be concealed using pixels from another frame or block. In one embodiment, the constraint is that the last two non-zero coefficients have the same magnitude. The constraint is added during compression after quantization but before variable-length coding by averaging the magnitudes and using the average magnitude for the last two non-zero coefficients. This minimizes visible distortion caused by the constraints and reduces computations.