https://bugs.kde.org/show_bug.cgi?id=490855
Bug ID: 490855
Summary: Frame timing issues/juddering when playing 24FPS
content in Kodi on kwin 6 when triple-buffering is
enabled
Classification: Plasma
Product: kwin
Version: 6.1.3
Platform: Kubuntu
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: performance
Assignee: kwin-bugs-n...@kde.org
Reporter: mich...@michaelmarley.com
Target Milestone: ---
SUMMARY
Since upgrading to Plasma 6, I have noticed that if I play 24FPS content
(specifically, DVDs) in Kodi, I get an odd judder (not the usual telecine
judder) where it appears sort of like frames aren't being dropped but instead a
few frames are being displayed with a shorter than normal pause between them
followed by a longer than usual pause. Oddly, kwin does not appear to be
dropping frames per se during this because if I run another application that
displays a 60FPS animation (such as vkcube-wayland) at the same time, that
application is smooth and I don't see any stuttering or frame drops.
This is not affected by any of the work in
https://bugs.kde.org/show_bug.cgi?id=488843; the issue occurs whether or not
those patches are applied. The issue does, however, only occur if
triple-buffering is enabled. If I force it disabled, the issue does not occur.
Even though kwin does not appear to be dropping frames, I did capture and
attach some performance statistics that I captured while reproducing the issue.
I need to do a bit more testing to be sure, but I think this issue doesn't
occur if the video is played in mpv rather than Kodi. The issue also didn't
occur on kwin 5.x.
STEPS TO REPRODUCE
1. Launch Plasma 6 and start Kodi
2. Play a 24FPS DVD in Kodi
OBSERVED RESULT
Abnormal juddering as described above
EXPECTED RESULT
Normal telecine judder/"smooth" playback
SOFTWARE/OS VERSIONS
Linux: 6.10.1
KDE Plasma Version: 6.1.3
KDE Frameworks Version: 6.4.0
Qt Version: 6.6.2
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