VDVI is a variable-rate version of DVI4, yielding speech bit rates of between 10 and 25 kb/s. It is specified for single-channel operation only. It uses the following encoding:
DVI4 codeword VDVI bit pattern
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0 00
1 010
2 1100
3 11100
4 111100
5 1111100
6 11111100
7 11111110
8 10
9 011
10 1101
11 11101
12 111101
13 1111101
14 11111101
15 11111111