#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 could be reproduced with the attached clips.
The output of QSV and VAAPI have the different number of B-frames between
non-B-frames of B frames.
QSV: 6 (not reach the maximum);
VAAPI: 2;
Hence it leads to the PSNR gap.
The root cause seems to be that QSV and VAAPI have the different
GopRefDist size by default.
VAAPI: 3
{{{
[hevc_vaapi @ 0x563647540b00] Using intra, P- and B-frames (supported
references: 3 / 1).
}}}
QSV: 9
{{{
[hevc_qsv @ 0x564c7866da40] GopPicSize: 248; GopRefDist: 9; GopOptFlag:
closed ; IdrInterval: 1
}}}
To verify:
Add "-bf 2" to match the default behavior of VAAPI
{{{
ffmpeg -v verbose -hwaccel qsv -qsv_device /dev/dri/renderD128 -c:v
hevc_qsv -i Netflix_FoodMarket_4096x2160_10bit_420_100mbs_60fps_7.h265
-c:v hevc_qsv -b:v 20M -bf 2 output.h265
}}}
(add -bf 2 makes no difference for VAAPI)
Before:
PSNR: average:28.524304
With "-bf 2":
PSNR: average:31.516557
Please help to verify and correct me if I was wrong.
--
Ticket URL: <https://trac.ffmpeg.org/ticket/8328#comment:6>
FFmpeg <https://ffmpeg.org>
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