 It is a part of the specification for both the SMPTE VC-1 codec and the ITU H.264 (ISO MPEG-4 AVC) codec.In contrast with older MPEG-/2/4 standards, the H.264 deblocking filter is not an optional additional feature in the decoder.It is a feature on both the decoding path and on the encoding path, so that the in-loop effects of the filter are taken into account in reference macroblocks used for prediction.