[M4IF Technotes] GMC

[Kasturi Rangam]

Is there some statistics regarding number of GMC macroblocks for a
MPEG4 bitstream. This will be useful to calculate the bandwidth
requirements.
Thanks,
Kasturi
Kasturi Rangam wrote:
> 
> Thanks for the information. I was wondering if we could calculate
> the motion vector range based on du[i] and dv[i] range. Of course
> if this range is more than the reference frame, then there is no
> point.
> 
> --Kasturi
> 
> "Sorin C. Cismas" wrote:
> >
> > I don't think there are any restrictions on the motion vectors.  I have
> > the same concern about the need to fetch 64 non-contiguous 2x2 pels
> > to predict a macroblock.  To reduce complexity and bandwidth requirements,
> > it is highly desirable to put some limits on du[i] and dv[i] for i>0.
> >
> > 2 and 3 warping points are usefull for zoom-in and zoom-out, however, it is
> > not realistic to assume, for example, a 10x zoom-out on an S(GMC) prediction.
> > A 50% or even 25% zoom-out restriction will be more than sufficient.
> > For 50%, this will translate to du[i]<W    and dv[i]<H    for i>0.
> > For 25%, this will translate to du[i]<W//2 and dv[i]<H//2 for i>0.
> > The 50% restriction will limit the macroblock luma prediction to 25x25.
> > The 25% restriction will limit the macroblock luma prediction to 21x21.
> >
> > Can these or similar restrictions be considered for a future corrigendum?
> >
> > Thanks,
> > Sorin Cismas
> >
> > > -----Original Message-----
> > > From: technotes-admin   lists.m4if.org
> > > [mailto:technotes-admin   lists.m4if.org]On Behalf Of Kasturi Rangam
> > > Sent: Friday, May 10, 2024 2:46 PM
> > > To: technotes   lists.m4if.org
> > > Subject: [M4IF Technotes] GMC
> > >
> > >
> > > I am trying to under GMC in MPEG4.
> > > Looks like you can have 0, 1, 2 or 3 sprite_warping_points.
> > >
> > > To decode a 0 and 1 sprite_warping_points macroblock, you can
> > > fetch the whole macroblock data from the reference to do pixel
> > > prediction.
> > >
> > > However, for 2 and 3 warping_points, the motion vector for each
> > > pixel can be anywhere in the reference frame. Thus we might need
> > > to perform 64 data fetches to predict one macroblock.
> > >
> > > Is there a range that can be calculated for each macroblock, so that
> > > we can fetch data only once?
> > >
> > > Thanks,
> > >
> > > Kasturi
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