https://bugs.kde.org/show_bug.cgi?id=516067
Bug ID: 516067
Summary: Jerky video playback of 60FPS video on 120Hz monitor
Classification: Plasma
Product: kwin
Version First 6.5.91
Reported In:
Platform: Kubuntu
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: performance
Assignee: [email protected]
Reporter: [email protected]
Target Milestone: ---
SUMMARY
When I play a 60FPS video on my 120Hz monitor, I get stuttering that randomly
ranges from apparent random frame drops all the way down to 30FPS. I've tested
this with the latest git builds of mpv and VLC and the issue is present with
both. In mpv, it works significantly better (but not perfectly) if
"--gpu-api=opengl --hwdec=vaapi" is passed rather than "--gpu-api=vulkan
--hwdec=vulkan". If OpenGL and VAAPI are used in combination with VRR, the
problem is eliminated. The problem also does not occur on a 60Hz screen.
While reproducing the problem, mpv does not report any frame drops.
I initially reported this as a bug in mpv
(https://github.com/mpv-player/mpv/issues/17410) and they suggested I try a
different compositor to prove whether the bug was in mpv or not. When I tried
Jay as they suggested, I got smooth playback of the same video using Vulkan for
both the GPU output and the decoding, which seems to indicate that kwin is at
fault here.
The issue occurs on both 6.5.5 and 6.5.91.
STEPS TO REPRODUCE
1. Play a 60FPS video on a 120Hz screen in mpv or VLC.
OBSERVED RESULT
Frame drops and/or near-30FPS peformance
EXPECTED RESULT
Smooth playback like with a 60Hz screen
SOFTWARE/OS VERSIONS
Linux: Linux mamarley-laptop 6.19.0-061900-generic #202602081706 SMP
PREEMPT_DYNAMIC Sun Feb 8 17:30:59 EST 2026 x86_64 x86_64 x86_64 GNU/Linux
KDE Plasma Version: 6.5.91
KDE Frameworks Version: 6.23
Qt Version: 6.10.2
ADDITIONAL INFORMATION
The video I tested with was
https://4kmedia.org/samsung-travel-with-my-pet-hdr-uhd-4k-demo/, but any 60FPS
video with smooth motion will reproduce the issue. For that video, the first 2
scenes with camera pans are the most obvious.
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