[Mp4-tech] Direct prediction in 1 MV (16x16) mode

[Sathish N]

Hello,
This question about Direct prediction is with regards to Sec 7.6.9.5 of
ISO/IEC 14496-2.
Is Direct mode Motion vector decoding (& sample Interpolation) always
required to be performed on 8x8 blocks (i.e 4MV mode)? OR is it that it
has to be performed on 16x16 macroblock (i.e 1 MV mode) if the
co-located MB is coded in 1MV mode & on 8x8 blocks if the co-located MB
is coded in 4MV mode ? 
Would some one please clarify ?
Thanks,
Sathish