[FFmpeg-trac] #9377(undetermined:new): QSV MPEG2 => H264 transcode PSNR dropped by 32%

FFmpeg trac at avcodec.org
Fri Oct 29 11:43:56 EEST 2021

#9377: QSV MPEG2 => H264 transcode PSNR dropped by 32%
             Reporter:  eero-t       |                    Owner:  (none)
                 Type:  defect       |                   Status:  new
             Priority:  normal       |                Component:
                                     |  undetermined
              Version:  git-master   |               Resolution:
             Keywords:               |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
Comment (by eero-t):

 According FFmpeg documentation, default for "-vsync" is "auto" which
 selects either "cfr" or "vfr".     Because I specified bitrate, not FPS, I
 assume FFmpeg to have selected VFR, which seems to drop timestamp only if
 consecutive frames would have duplicate timestamp.

 Are you saying that this is MediaSDK timestamp handling bug exposed by the
 FFmpeg change (to actually tell MediaSDK that there was no timestamp on
 some frame), one that can be only fixed on MediaSDK side? (will you file

 As PSNR / SSIM calculations do frame-by-frame comparison, any change in
 frame timestamps during transcoding would make things go wrong as it
 affect frame content => should I '''always''' use "-vsync passtrough" (and
 "-an") on transcode operation intended for PSNR / SSIM calculations? And
 for performance comparisons?

 PS. Is the cause for my other (more recent) PSNR bug similar:
 https://trac.ffmpeg.org/ticket/9481 ?
Ticket URL: <https://trac.ffmpeg.org/ticket/9377#comment:9>
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