SMPTE RP 202 : 2008

Equipment conforming to this practice will minimize artifacts in multiple generations of encoding and decoding by optimizing macroblock alignment. As MPEG-2 becomes pervasive in emission, contribution, and distribution of video content, multiple compression and decompression (codec) cycles will be required. Concatenation of codecs may be needed for production, post-production, transcoding, or format conversion. Any time video transitions to or from the coefficient domain of MPEG-2 are performed, care must be exercised in alignment of the video both horizontally and vertically as it is coded from the raster format or decoded and placed in the raster format.