the locations of the reference pixel blocks 114 in the reference pictures 103 are recorded as a motion vectors the motion vectors describes the spatial displacement between the block 113 and the reference pixel block 114 in avc the blocks 113 can be 16 u00d7 16 pixels also called a macroblock or smaller such as 16 u00d7 8 8 u00d7 8 8 u00d7 4 4 u00d7 8 4 u00d7 4 pixels or other sizes and shapes a data structure representing the picture 103 includes the encoded blocks 113 and the motion vectors in both mpeg 2 predicted pictures 103 can be predicted from as many as two reference pictures and in avc predicted pictures 103 can be predicted from one two or more reference pictures intracoded pictures or i pictures are not predicted from other pictures in mpeg 2 predicted coded pictures or p pictures are predicted from one reference picture that is displayed prior to the p picture in avc each p type block is predicted from any one of a plurality of reference pictures in mpeg 2 bidirectionally predicted pictures or b pictures are predicted from one reference picture that is displayed prior to the b picture and another reference picture that is displayed after the b picture in avc each b type or bi predicted block is predicted from any two of a plurality of reference pictures i 0 b 1 b 2 p 3 b 4 b 5 and p 6 are exemplary pictures the arrows illustrate the prediction dependence of each picture for example picture b 2 is dependent on reference pictures i 0 and p 3 the foregoing data dependency among the pictures requires decoding of certain pictures prior to others additionally the use of.