H.261 Datasheet, PDF (16/31 Pages) List of Unclassifed Manufacturers – LINE TRANSMISSION OF NON-TELEPHONE SIGNALS

TABLE 2/H.261
VLC table for MTYPE
Prediction
MQUANT
MVD
CBP
TCOEFF
VLC
Intra
Intra
Inter
Inter
Inter + MC
Inter + MC
Inter + MC
Inter + MC + FIL
Inter + MC + FIL
Inter + MC + FIL
x
0001
x
x
0000 001
x
x
1
x
x
x
0000 1
x
0000 0000 1
x
x
x
0000 0001
x
x
x
x
0000 0000 01
x
001
x
x
x
01
x
x
x
x
0000 01
NOTES
1 “x” means that the item is present in the macroblock.
2 It is possible to apply the filter in a non-motion compensated macroblock by declaring it as MC + FIL but
with a zero vector.
4.2.3.4 Motion vector data (MVD) (Variable length)
Motion vector data is included for all MC macroblocks. MVD is obtained from the macroblock vector by subtracting the
vector of the preceding macroblock. For this calculation the vector of the preceding macroblock is regarded as zero in the
following three situations:
1) evaluating MVD for macroblocks 1, 12 and 23;
2) evaluating MVD for macroblocks in which MBA does not represent a difference of 1;
3) MTYPE of the previous macroblock was not MC.
MVD consists of a variable length codeword for the horizontal component followed by a variable length codeword for the
vertical component. Variable length codes are given in Table 3.
Advantage is taken of the fact that the range of motion vector values is constrained. Each VLC word represents a pair of
difference values. Only one of the pair will yield a macroblock vector falling within the permitted range.
4.2.3.5 Coded block pattern (CBP) (Variable length)
CBP is present if indicated by MTYPE. The codeword gives a pattern number signifying those blocks in the macroblock for
which at least one transform coefficient is transmitted. The pattern number is given by:
32 · P₁ + 16 · P₂ + 8 · P₃ + 4 · P₄ + 2 · P₅ + P₆
where P_n = 1 if any coefficient is present for block n, else 0. Block numbering is given in Figure 10.
The codewords for CBP are given in Table 4.
Recommendation H.261 (03/93)
13