Provided is a video decoding method including: obtaining constrained prediction information indicating whether a constrained intra prediction mode is enabled; generating reconstructed samples of a current block by using prediction samples of the current block and residual samples of the current block; when the constrained intra prediction mode is enabled by the constrained prediction information and a prediction mode of a neighboring block is not an intra prediction mode, determining a padding value corresponding to a neighboring sample adjacent to outside of a boundary between the current block and the neighboring block, by using the reconstructed samples of the current block; and performing post-reconstruction filtering on the current block, by using the padding value corresponding to the neighboring sample.