[M4IF Technotes] Stuffing bytes in MPEG-4 version 2

[Paulo Nunes]

Dear Christoph,
	up to my knowledge you may use stuffing MBs for I- and P-VOPs for both
rectangular and non rectangular VOLs. The problem however arises when,
after encoding a VOP, you find that the VBV will very likely underflow
(at the encoder).
	For rectangular VOLs you may add at the end of the VOP a few
(not_coded='0' - "1 bit" + mcbpc = 'stuffing' - "9 bits") before the
next VOP_START_CODE.
	For non-rectangular VOLs however you can not do this because you can
not send meaningful shape information for the MB
(mb_binary_shape_coding() function). Thus, either you send your
'stuffing' MBs before the last non-transparent MB of the VOP, or you use
the STUFFING_START_CODE + n STUFFING_BYTEs.
	What I don't understand is why it is explicitly not allowed to use the
STUFFING_START_CODE + n STUFFING_BYTEs mechanism in all cases.
Thanks for your comments,
	Paulo Nunes
Christoph Stadler wrote:
> 
> Paulo Nunes wrote:
> >
> > Dear all,
> >
> >         in MPEG-4 Part2:Visual, the mechanism of inserting stuffing bytes (1
> > stuffing_start_code + n stuffing_bytes) for proper VBV operation is only
> > allowed for B- and S-VOPs for rectangular VOLs, while for
> > non-rectangular VOLs it is allowed for all VOP types.
> >
> >         I would very much appreciate if someone could point me the reason, if
> > there is one, why this mechanism can not be used for I and P rectangular
> > VOPs.
> >
> > Thanks in advance for your help,
> >
> >         Paulo Nunes
> >
> > _______________________________________________
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> > Technotes   lists.m4if.org
> > http://lists.m4if.org/mailman/listinfo/technotes
> 
> Dear Paulo,
> 
> for rectangular I-VOPs and P-VOPs you are instead allowed to send
> "stuffing macroblocks".
> I don't know WHY there is this difference between stuffing macroblocks
> and stuffing bytes, but at least the VBV management can be done in
> both cases.
> 
> Hope this helps,
> 
>         Christoph Stadler
> 
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