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Section 3.4. The H.263 Standard 51
176 luma pels (88 chroma)
GOB 1
GOB 2
GOB 3
GOB 4 144 luma
QCIF picture frame GOB 5 lines
GOB 6 (72 chroma)
GOB 7
GOB 8
GOB 9
Group of MB MB MB MB MB MB MB MB MB MB MB
blocks (GOB) 1 2 3 4 5 6 7 8 9 10 11
Y ′
C′ C′
1 2 B R
Macroblock (MB) 16 lines 5 6 8
3 4
8
16 pels
1 8
Block 8 lines
57 64
8 pels
Figure 3.2: H.263 picture structure for a QCIF frame
decision to transmit an MB or not is not part of the standard. The di1erent
Jags are encoded within the picture and MB headers.
3.4.3.3 Motion Estimation and Compensation
Without options, the encoder estimates one motion vector per MB. Both hori-
zontal and vertical components of the vector have integer or half-integer values
and are restricted to the range [−16; +15:5]. A positive value of the horizon-
tal or vertical component means that the prediction is made from pels in
the reference picture that are spatially to the right or below the pels being
