[Mp4-tech] (H.264 video)about Interprediction sample values

[kavita.chachadi1 wipro.com]

Hello all,
When we are constructing the sample values ,we have
xIntL = xAL + ( mvLX[ 0 ] >> 2 ) + xL 
yIntL = yAL + ( mvLX[ 1 ] >> 2 ) + yL
xFracL = mvLX[ 0 ] & 3 
yFracL = mvLX[ 1 ] & 3
so the input to the prosess will be 
xIntL,yIntl,xFracL,yFracL.
Depending on xFracl,yFracL  values the decision is taken whether to construct full sample pel values,Half pel sample value
or Quarter pel sample values.
Why xFracL and yFracL is anded with 3.(I know to fetch last 2 bits),what is the purpose?
How exactly quarter pel motion vector is encoded?
Thanks in advance.
Regards,
Kavita
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