[XviD-devel] B frame help

Christoph Lampert chl at math.uni-bonn.de
Sat Feb 8 01:16:42 CET 2003


On Sat, 8 Feb 2003, Zoltan Kocsi wrote:
> This might be something I do wrong, actually I am sure that that's
> where the major problem is. My motion vectors are always in the
> [-32,31] range, fcode is always 1. Only forward or backward vector
> is used, none of the other methods available for B frames. Only one
> vector per macroblock, no quadrants. 
> 
> I use the exact same encoder (and predictor) what I use for the 
> P frames and that might be the heart of the problem. I do not want
> to break the list ethics, but if it is OK, I can attach a (reasonably
> small) .tar.gz file with the 3 test frames and the result frames.
> Maybe someone who was working a lot with B frames looks at them
> and recognises the problem immediately and can tell me me what 
> part of the standard I missed or misinterpreted. The images
> are small, 320x240 in PPM format, mostly black so they compress 
> very well. Also, when I generate the bitstream I also create a 
> bitstream debug file which looks like this:

Maybe a predictor problem? Those happen easily, because MV prediction is
slightly different than for P-frames. 

gruel



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