[FFmpeg-trac] #8328(undetermined:new): QSV gives much worse PSNR/SSIM for HEVC transcode than VA-API or MediaSDK

[FFmpeg]

#8328: QSV gives much worse PSNR/SSIM for HEVC transcode than VA-API or MediaSDK
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             Reporter:  eero-t       |                    Owner:
                 Type:  defect       |                   Status:  new
             Priority:  normal       |                Component:
                                     |  undetermined
              Version:  unspecified  |               Resolution:
             Keywords:               |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
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Comment (by eero-t):

 "-bf 2" option gives same good PSNR for QSV as with VA-API, in the full
 video (41 instead of 25).

 It reduces bitrate 3% from the requested 20Mbit/s i.e. it seems to make
 QSV bitrate slightly less accurate (VA-API bitrate is closer to requested,
 at least in this case).

 While "-bf 2" option didn't do anything for VA-API, giving "-bf 6" option
 for it, dropped VA-API PSNR marginally (<1%).

 Is that huge PSNR drop with larger QSV B-frame count a driver issue, or
 should FFmpeg QSV default be just changed?

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Ticket URL: <https://trac.ffmpeg.org/ticket/8328#comment:7>
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