[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 fulinjie):

 It's not an issue IMHO.

 For VAAPI hevc encoder, the default parameter for bf is 2:
 https://github.com/FFmpeg/FFmpeg/blob/master/libavcodec/vaapi_encode_h265.c#L1265

 For QSV hevc encoder, the default parameter for bf is 8:
 https://github.com/FFmpeg/FFmpeg/blob/master/libavcodec/qsvenc_hevc.c#L261

 And for some historical reasons, it was set to 8 on purpose:
 https://github.com/FFmpeg/FFmpeg/commit/a43905f4ae261bdde87c300901d867b31961f57b


 Hence in this performance test, a better choice could be setting "-bf"
 with the same value explicitly for both VAAPI and QSV, instead of using
 the default settings of codecs(usually parameters are different between
 each codec).

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Ticket URL: <https://trac.ffmpeg.org/ticket/8328#comment:8>
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