[Mp4-tech] Regarding padding in MPEG-4 part 2

[Rickard Sjöberg (KI/EAB)]

Dear experts,
assume that a simple profile video stream with height and width of 120 and 170 pixels respectively shall be decoded. The bounding rectangle of the reference VOP is 128x176. Now my question is whether you should pad outside of 120x170 or 128x176 when referencing pixels for motion compensation?
The relevant part of the standard is section 7.6.4 i believe (I looking at the 3rd edition, that's ISO/IEC 14496-2:2004, N5515):
The coordinates of a reference sample in the reference VOP, (yref, xref) is determined as follows :
xref = MIN ( MAX (xcurr+dx, vhmcsr), xdim+vhmcsr-1 )
yref = MIN ( MAX (ycurr+dy, vvmcsr), ydim+vvmcsr-1)
My interpretation of this is that padding should be done outside of 128x176 (this means that the pixels outside of 120x170 but inside of 128x176 shall be left as they were decoded), is this correct?
Is there any conformance bitstream that tests this behaviour?
/
Rickard Sjoberg
Ericsson