https://bugs.kde.org/show_bug.cgi?id=527666
Bug ID: 527666
Summary: KWin 6.8 regression: severe dropped frames in mpv
fullscreen playback on external TV (workaround:
KWIN_DRM_NO_AMS=1)
Classification: Plasma
Product: kwin
Version First unspecified
Reported In:
Platform: CachyOS
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: wayland-generic
Assignee: [email protected]
Reporter: [email protected]
Target Milestone: ---
SUMMARY
After upgrading KWin from 6.7.5 to 6.8.0, fullscreen video playback in mpv on
an external TV became unusable due to heavy frame drops. Setting the
environment variable KWIN_DRM_NO_AMS=1 completely resolves the issue, which
suggests the regression is related to the new direct scanout / adaptive sync
(AMS) code path enabled by default in 6.8.
STEPS TO REPRODUCE
1. Connect a Panasonic Plasma TV (supports 23.976 / 24 / 50 / 59.94 / 60 Hz) to
the PC via HDMI.
2. Use a script (mpv-kscreen-doctor.lua) to switch the TV to the refresh rate
matching the video file (e.g. 23.976 Hz).
3. Play any HD video file with mpv in fullscreen.
OBSERVED RESULT
Constant dropped frames; playback is stuttering and unwatchable. The same setup
worked perfectly with KWin 6.7.5.
EXPECTED RESULT
Smooth playback as with KWin 6.7.5.
SOFTWARE/OS VERSIONS
Operating System: CachyOS Linux (Arch-based)
KDE Plasma Version: 6.8.1
KDE Frameworks Version: 6.31.0
Qt Version: 6.12.0
Kernel Version: 7.3.0-3-cachyos (64-bit)
Graphics Platform: Wayland
ADDITIONAL INFORMATION
Hardware: AMD Ryzen 3 3200G with Radeon Vega 8 Graphics, 16 GB RAM.
Regression window: between KWin 6.7.5 and 6.8.0 (updated on 16 October 2026).
Workaround: KWIN_DRM_NO_AMS=1 in /etc/environment fixes the dropped frames
completely.
I am happy to provide logs (journalctl, kwin debug output) or test patches if
needed.
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