Michael Niedermayer (12022-08-04):
> I suspect several filters are somewhat "wrong"
> for example hflip fliping 4:1:1
> would turn a:   *--- into ---*
> where * is teh chroma sample location, i dont think it updates the chroma
> sample location metadata nor does it apply some filter to chroma to shift by
> 3/4 samples. so it looks wrong, one of the 2 is neeed.
> 
> vf_scale contains some code to handle this but iam not seeing code considering
> the input and output frames chroma location metadata
> 
> All this leads to small errors, often probably not vissible
> when you have one one chroma sample for 4 luma samples you will always have
> some artifacts on sharp color edges, if the location of the chroma sample
> is wrong the artifact would be more to one side of a diagonal edge than the
> other. If the locations are correct it should be more symmetric in theory.

I think I understand. Would it be ok to apply this with the added
comment:

* Note: this is a quick mnemonic representation of the pixels; actual
* interaction between chroma and luma is more complex, see
* AVChromaLocation in pixfmt.h.

?

Regards,

-- 
  Nicolas George