picture. The partitioning is specified by the macroblock to slice group map. 3.144 slice group map units: The units of the map unit to slice group map. 3.145 slice header: A part of a coded slice containing the data elements pertaining to the first or all macroblocks represented in the slice. 3.146 source: Term used to describe the video material or some of its attributes before encoding. 3.147 SP slice: A slice that may be coded using intra prediction or inter prediction with quantisation of the prediction samples using at most one motion vector and reference index to predict the sample values of each block. An SP slice can be coded such that its decoded samples can be constructed identically to another SP slice or an SI slice. 3.148 start code prefix: A unique sequence of three bytes equal to 0x000001 embedded in the byte stream as a prefix to each NAL unit. The location of a start code prefix can be used by a decoder to identify the beginning of a new NAL unit and the end of a previous NAL unit. Emulation of start code prefixes is prevented within NAL units by the inclusion of emulation prevention bytes. 3.149 string of data bits (SODB): A sequence of some number of bits representing syntax elements present within a raw byte sequence payload prior to the raw byte sequence payload stop bit. Within an SODB, the left-most bit is considered to be the first and most significant bit, and the right-most bit is considered to be the last and least significant bit. 3.150 sub-macroblock: One quarter of the samples of a macroblock, i.e., an 8x8 luma block and two corresponding chroma blocks of which one corner is located at a corner of the macroblock for a picture that has three sample Rec. ITU-T H.264 (01/2012) arrays or an 8x8 luma block of which one corner is located at a corner of the macroblock for a monochrome picture or a picture that is coded using three separate colour planes. 3.151 sub-macroblock partition: A block of luma samples and two corresponding blocks of chroma samples resulting from a partitioning of a 