erived by invoking the inverse macroblock scanning process in clause 6.4.1 with mbAddrN as the input and the output is assigned to (xx, yM). Depending on the variable MbaffFrameFlag and the macroblock mbAddrN, the sample value p[x,y] is derived as follows: If MbaffFrameFlag is equal to 1 and the macroblock mbAddrN is a field macroblock, x,y]=cSL[xM+ xW,yM+ 2 * yW] (8-44) Otherwise (MbaffFrameFlag is equal to 0 or the macroblock mbAddrN is a frame macroblock), p[x,y]=cS[xM+ xW,yM+ yW] (8-45) Rec. ITU-T H.264 (01/2012) When samples p[ X, -1], with X = 4..7, are marked as "not available for Intra 4x4 prediction," and the sample p[ 3, -1] is marked as "available for Intra_4x4 prediction," the sample value of p[3,-1] is substituted for sample values p[ X, -1], with X = 4..7, and samples p[ X, -1], with X = 4..7, are marked as "available for Intra_4x4 prediction". NOTE - Each block is assumed to be constructed into a picture array prior to decoding of the next block. Depending on Intra4x4PredMode[ luma4x4BlkIdx ], one of the Intra_4x4 prediction modes specified in clauses 8.3.1.2.1 to 8.3.1.2.9 is invoked. 8.3.1.2.1 Specification of Intra_4x4_Vertical prediction mode This Intra_4x4 prediction mode is invoked when Intra4x4PredMode[ luma4x4BlkIdx ] is equal to 0. This mode shall be used only when the samples p[ X, ,-1] with X = 0..3 are marked as "available for Intra_4x4 prediction". The values of the prediction samples pred4x4L[ X, y ], with X, y = 0..3, are derived by pred4x4L[x,y]=p[x,-1],withx, y = 0..3 (8-46) 8.3.1.2.2 Specification of Intra_4x4_Horizontal prediction mode This Intra_4x4 prediction mode is invoked when Intra4x4PredMode[luma4x4BlkIdx] is equal to 1. This mode shall be used only when the samples p[-1,y], with y = 0..3, are marked as "available for Intra_4x4 prediction". The values of the prediction samples pred4x4L X, y ], with X, y = 0..3, are derived by 4x41[x,y]=p[-1,y], with x,y = 0..3 (8-47) 8.3.1.2.3 Specification of Intra_4x4_DC prediction mode This Intra_4x4 prediction mode is invoked when Intr