Query regarding pattern_code / coded block pattern /

Hi All,

I am quite new to MPEG-4 and in the process of developing an mpeg4 SP
decoder.In this Xvid opensource is quite helpful. I have the following
queries:

1- how to find the cbp for a block. Is it same like pattern_code in ( ISO
6.2.7, Block( ) ) ? I think it represents coded blocks in the macroblock.

2- Can a block have  Zero DC Coefficient ?

3- How to find that All AC Coefficients of a block or Zero ?

4- If the cbp/pattern_code is zero, then do we have to consider pDst[0-63] =
0 , meaning that all the coefficients are zero.

5- and Finally on line 80 in decoder.c the statement " if (quant <
intra_dc_threshold) " is used instead of use_intra_dc_VLC (ISO/IEC page 58,
MPEG4 Visual). I dont know how this can be used for this test.

Sorry for asking some poor questions but I am quite new to MPEG and need ur
help. Other wise i will be in great trouble. Thanks for your kind help.

*Kind Regards,
*
Anwar  Sajid