[FFmpeg-trac] #5822(avfilter:new): filter "scale_npp" fails to select correct algorithm (Nvidia CUDA/NPP scaler)

FFmpeg trac at avcodec.org
Mon Sep 5 22:40:58 EEST 2016

#5822: filter "scale_npp" fails to select correct algorithm (Nvidia CUDA/NPP
             Reporter:  sdack        |                    Owner:
                 Type:  defect       |                   Status:  new
             Priority:  normal       |                Component:  avfilter
              Version:  git-master   |               Resolution:
             Keywords:  scale_npp,   |               Blocked By:
  interp_algo, Nvidia, CUDA, NPP     |  Reproduced by developer:  0
             Blocking:               |
Analyzed by developer:  0            |

Comment (by sdack):

 Although one can influence the result with a different pixel shift and
 thereby produce distinguishable images from the algorithms does this also
 cause a minor shift in the image itself, which isn't acceptable.

 After reading the Nvidia forums did I notice a dev saying there were
 ''"We (NVIDIA) recently found a bug in the rotation code which at some
 scale factors can cause the last source pixel in a row or column to not be
 sampled. ResizeSqrPixel contains a similar test which probably also needs
 fixed. It would be great if you could send us an example of a failure
 case. In the meantime, a possible work around would be to increase
 oSrcROI.width and oSrcROI.height by 1. To be safe in all cases however,
 this may require that you increase the memory allocated for your source
 image by 1 in both width and height." (Posted 07/26/2016)
 This doesn't sound quite like the issue here, but I am hoping an Nvidia
 dev will take a look at this since there is already one known bug. I have
 posted the problem on the Nvidia forums.


Ticket URL: <https://trac.ffmpeg.org/ticket/5822#comment:4>
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