Bug 490855

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