[M4IF Technotes] h.263 motion vector predictor

[Herbert Thoma]

Ariel David schrieb:
> 
> Yes,
> there are GOB headers in the stream.
> So I understand that a change of GOB is like a change of VOP .
> Prediction cannot be made from one GOB to another just as it can not be made from one VOP to another.
> 
> Is this correct?

Yes, this is correct. But the analogon of GOB in H.263 is Video Packet (VP)
in MPEG-4, not Video Object Plane (VOP).
> Ariel
> 
> -----Original Message-----
> From: Gary Sullivan [mailto:garysull   windows.microsoft.com]
> Sent: Saturday, May 24, 2024 11:56 PM
> To: Ariel David
> Subject: RE: [M4IF Technotes] h.263 motion vector predictor
> 
> Does that stream have GOB headers in it?  I'm trying to remember whether
> the presence of GOB headers cuts the prediction of MVs from the MBs in
> the row above.  A quick look in either the H.263 or MPEG-4 spec should
> answer that.
> 
> -Gary
> 
> +> -----Original Message-----
> +> From: Ariel David [mailto:Ariel.David   ParthusCeva.com]
> +> Sent: Thursday, May 22, 2024 12:27 AM
> +> To: Gary Sullivan
> +> Subject: RE: [M4IF Technotes] h.263 motion vector predictor
> +>
> +>
> +> Hi,
> +> I'm sorry to nag about this issue, but there is something I
> +> still don't understand.
> +>
> +> I am currently working on decoding the test stream
> +> "vcon-ge-16-L1.m4v".  This is a short header video stream.
> +> When I decode the motion vectors using the median predictor
> +> the output picture comes out bad.
> +> When I decode the motion vectors using the left macroblock
> +> only as the predictor the picture comes out OK.
> +> This is the reason for my questions about the subject.
> +> There is simply something that I don't understand here.
> +>
> +> As far as I can see there can a number of answers:
> +> 1.  The stream was not encoded correctly in that the
> +> predictors used in the encoder are not median.
> +> 2.  This is some special case of prediction that I am not aware of.
> +>
> +> Thanks for the previous answers,
> +>
> +> Ariel
> +>
> +>
> +>
> +>
> +> -----Original Message-----
> +> From: Gary Sullivan [mailto:garysull   windows.microsoft.com]
> +> Sent: Wednesday, May 21, 2024 7:23 PM
> +> To: Ariel David; technotes   lists.m4if.org
> +> Subject: RE: [M4IF Technotes] h.263 motion vector predictor
> +>
> +>
> +> Skipped MBs in P pictures use (0,0) MVs.  Doesn't matter
> +> whether short
> +> header or not.
> +>
> +> -Gary S.
> +>
> +> +> -----Original Message-----
> +> +> From: technotes-admin   lists.m4if.org
> +> +> [mailto:technotes-admin   lists.m4if.org] On Behalf Of Ariel David
> +> +> Sent: Wednesday, May 21, 2024 8:25 AM
> +> +> To: technotes   lists.m4if.org
> +> +> Subject: RE: [M4IF Technotes] h.263 motion vector predictor
> +> +>
> +> +>
> +> +> Maybe the problem is in my median prediction.
> +> +>
> +> +> are predictors that are skipped macroblock computed
> +> +> differently or are they considered 0,0 motion vector.
> +> +> For example:
> +> +> if the top left MV is 0,0, the top MV is 1,1 and the left is
> +> +> skipped will the predictor be 0,0 (regular median) or 1,1
> +> +> (since the left is not considered).
> +> +>
> +> +> Ariel
> +> +>
> +> +> -----Original Message-----
> +> +> From: Herbert Thoma [mailto:tma   iis.fhg.de]
> +> +> Sent: Wednesday, May 21, 2024 5:39 PM
> +> +> To: Ariel David
> +> +> Cc: technotes   lists.m4if.org
> +> +> Subject: Re: [M4IF Technotes] h.263 motion vector predictor
> +> +>
> +> +>
> +> +> Ariel David schrieb:
> +> +> >
> +> +> > Hi,
> +> +> >
> +> +> > I am trying to decode mpeg-4 video files with short header
> +> +> (h.263 format).
> +> +> > I've looked though the mpeg-4 standard and found not
> +> +> mention of a different method for motion vector predictor.
> +> +> > The mpeg-4 method is the median of the 3 adjacent macroblocks.
> +> +> > This does not seem to work in h.263 (mpeg-4 with short headers).
> +> +>
> +> +> Why not? It's exactly the same in H.263.
> +> +>
> +> +>  Herbert.
> +> +>
> +> +> > I assume it's more like mpeg-2, either left or top
> +> +> macroblock, but I can't find any mention in the standard.
> +> +> >
> +> +> > Can someone help me out?
> +> +> >
> +> +> > Thanks,
> +> +> >
> +> +> > Ariel
> +> +> >
> +> +> > _______________________________________________
> +> +> > Technotes mailing list
> +> +> > Technotes   lists.m4if.org
> +> +> > http://lists.m4if.org/mailman/listinfo/technotes
> +> +>
> +> +> --
> +> +> Herbert Thoma
> +> +> FhG-IIS A, Studio Department
> +> +> Am Wolfsmantel 33, 91058 Erlangen, Germany
> +> +> Phone: +49-9131-776-323
> +> +> Fax:   +49-9131-776-399
> +> +> email: tma   iis.fhg.de
> +> +> www: http://www.iis.fhg.de/
> +> +>
> +> +>
> +> +> _______________________________________________
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> +> +>
> +>
> +>
> 
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-- 
Herbert Thoma
FhG-IIS A, Studio Department
Am Wolfsmantel 33, 91058 Erlangen, Germany
Phone: +49-9131-776-323
Fax:   +49-9131-776-399
email: tma   iis.fhg.de
www: http://www.iis.fhg.de/