The maximum size of H.263 encoded video frame is of (k*16384) bits where k=4,16,32.
The value of k varies w.r.t. the resolution .
QCIF and S-QCIF,k=4.
4CIF , k=16.
16CIF, k=32.

For more on Video Resolution: http://en.wikipedia.org/wiki/Common_Intermediate_Format