The method for block coding data, such as video data, via a compression operation includes applying to input-data blocks a discrete-cosine-transform (DCT) operation and a quantization operation to produce compressed-data blocks. The compressed-data blocks are subjected to a coding operation to obtain compressed output flows; and an inverse-quantization operation and an inverse-discrete-cosine-transform (IDCT) operation are applied on the compressed-data blocks to obtain reconstructed blocks. The method includes controlling generation of mismatch errors from the input-data blocks by detecting data blocks from the input-data blocks and compressed-data blocks that are liable to cause mismatch errors, and modifying the blocks that are liable to cause mismatch errors prior to the coding operation.