#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):
Recap of the findings:
* Individual frames contents are fine, checked by converting both files to
raw and calculating PSNR
* Forcing frame-rate for the QSV encoded file in PSNR calculation with "-r
60" also gives good PSNR, although encoded video frame-rate is already 60
* When calculating PSNR for more frames, PSNR gets worse
One explanation that I could think for this is:
* Encoded video includes individual frame times (offsets?) in addition to
overall video frame rate
* FFmpeg does PSNR comparison by aligning video frames to a timeline based
on individual frame timings (unless one specifies -r option), instead of
comparing frames as-is
* Timings for individual encoded frames drift (are truncated or rounded
up?) with QSV when it uses higher B-frame count => bug
Linjie, could you check my theory; get the individual frame timings for
both videos out of FFmpeg and check whether they differ?
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Ticket URL: <https://trac.ffmpeg.org/ticket/8328#comment:11>
FFmpeg <https://ffmpeg.org>
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