[M4IF Technotes] h.263 motion vector predictor

[Herbert Thoma]

Ariel David schrieb:
> 
> Maybe the problem is in my median prediction.
> 
> are predictors that are skipped macroblock computed differently or are they considered 0,0 motion vector.

Skipped macroblocks (not_coded = 1) are considered as INTER macroblocks with
0,0 motion vector and no coefficient data.
> 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).

The predictor is 0,0 in this case.
But it is the top _right_ MV, top MV and left MV:
    +---+---+
    | 2 | 3 |  
+---+---+---+
| 1 | x |
+---+---+
x is the current macroblock, the median of 1, 2, and 3 is the predictor.
 Herbert.
> 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
> >
> > _______________________________________________
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> > 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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-- 
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/