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MPEG2's motion vector problem?

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davyzhu

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Hi all,

I encounter a problem when reading MPEG2's motion vector.
The vector[r][t]'s definition:
r==0:first motion vector in MB;r==1:second motion vector in MB;
s==0:forward motion vector;s==1:backward motion vector;
t==0:horizontal;t==1:vertical;

What's r's first and second mean??

e.g. If I have a picture sequance I1 B2 B3 P4 B5 B6 P7. The frame have frame prediction.
And If B2 have one forward motion vector to I1 and one backward motion vector to P4.
Is the vector[0][0][t] and vector[0][1][t]?
Or Is the vector[0][0][t] and vector[1][1][t]?
Or others??

Any suggestions will be appreciated!
Best regards,
Davy
 

Hi,
There are different types of predictions in MPEG standard. One kind is Predicting a frame MB from a Frame picture in which case a single MV is enogh for a MB. But there are cases like Field MB predictions in Frame pictures and Dual Motion Vectors. These prediction cause another type of variation in Motion vectors and that is the reason you have the first and second motion vectors. For more details read the MPEG2 Specification.
Hope this was useful.

Regards,
KJN
 

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    davyzhu

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