[XviD-devel] Some mismatch in chroma

[Yousuf Ali]

Hi guys,
   
  New member here, first email so please forgive me if I am not doing this properly.
   
  To get straight to the point, I have a compressed (raw, m4v) mpeg4 video stream that I decoded with the xvid 1.1.2 codec (using decraw). I also have an mpeg-4 analyzer (at my workplace) called Vprove (from Vqual) and I decoded the same stream with that.
   
  I see some mismatch in the chroma channels. The errors are small though, around +/- 5 in U and V channel outputs as far as I saw.
   
  I want to know if this is a known fact? If it is, then does this mean that xvid is not 100% compliant? It could even be the case that Vprove might be wrong, question is, how do we know?
   
  If you guys are interested to analyse this further, I can send you the compressed stream, source YUVs and the analyzer trace and decoded YUV (from Vprove) for this particular stream.
   
  On a side note, can I ask you what is the method of testing you employ to verify compliancy? Since the errors are small enough, not really noticable in output picture, so does that "good enough" mean compliant enough as well?
   
  I only ask about the testing methodology because I am working on an mpeg-4 encoder model myself (at home) and up until now, my main validation tool was xvid (decraw). And now I see a stream generated by my encoder that matches Vprove but not xvid :(
   
   
   
  Regards,
   
  Yousuf

 
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