https://bugs.kde.org/show_bug.cgi?id=516067

--- Comment #2 from Michael Marley <[email protected]> ---
(In reply to Zamundaaa from comment #1)
> On my laptop I see some individual frame drops from time to time with the
> Vulkan decoder, but it uses the CPU quite heavily (maybe Mesa isn't set up
> to support the codec or something), so it's not particularly surprising to
> me.
> VLC (apart from not playing back HDR videos correctly) seems to be fine
> though.
I checked both the CPU and GPU usage while this was happening and there was no
indication that the system wasn't powerful enough to play the video smoothly.

> How did you determine it drops to 30FPS? Just based on visuals, or also
> measurements of some sort?
> If you run mpv with mangohud, do you see the frame drops in the frame time
> graph?
Just based on visuals.  I ran it with mangohud and it showed a nearly-flat
green line for the entire video (while the problem was definitely being
reproduced) with a CPU usage of <5% and a GPU usage of ~40%, so it doesn't seem
to be showing any frame drops if I am understanding the graph correctly.  I
also tried it with Vulkan/VAAPI and OpenGL/VAAPI.  The line was still green and
flat for both of those and the problem still occurred (except for OpenGL/VAAPI
fullscreen with VRR).

> > While reproducing the problem, mpv does not report any frame drops.
> Maybe the frames are presented at the wrong time, rather than dropped. Like
> 12--34--56--78-- instead of 1-2-3-4-5-6-7-8-. Or something more chaotic...
> It's possible that mpv doesn't handle a lack of commit-timing support well,
> and this will be gone once it's implemented in Plasma 6.7.
That sounds promising.  It isn't 12--34--56--78--, but it feels like some more
chaotic form of frames being displayed at the wrong times and/or for the wrong
amount of time sounds right.  The commit-timing thing sounds right as the mpv
people specifically requested I try a compositor with wp_commit_timing support.
 I'm very happy to hear that this extension will be supported in 6.7.  I will
anxiously await that.

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