Very strange VLC multi monitor fullscreen problem

First, I swear this is not a very late april fools joke.

I have a multi monitor setup: 2 iiyama G-Master GB2788HS (27", 144Hz) connected both to a NVidia Geforce RTX 3080.

My problem is with VLC fullscreen (either video or streams, doesn’t matter). When I fullscreen a VLC window (double click or press F) on any monitor, it sometimes goes black, sound still playing normally. Moving the mouse still displays the controls, so the problem is not that the monitor doesn’t display anything. Removing fullscreen displays the stream/video normally, so the problem is exclusively while fullscreen.

Now, when I say “sometimes”, that is because I cannot in very definitive terms express when this happens. I can reproduce the problem in the following way: Open a stream/video in VLC, maximize it on monitor 1 (plays fine in fullscreen on monitor 1), normalize (removing fullscreen), move it to the monitor 2, then fullscreen on monitor 2, and the fullscreen image goes dark. I’ve had the problem on monitor 1 as well, after having maximized a video/stream on monitor 2, but that is more difficult to reproduce.

My current workaround is closing the stream/video down, then restarting. VLC remembers which monitor had the VLC last, so it reopens on the monitor where I closed it last, then fullscreen, and that always works.

I had something similar and it required a setting in Tools > Preferences > Video > Output to be set to X11 video output (XCB) . Of course this may not be the same and your settings may be different but it may help you.

Thanks for the info. It sounded promising, but my output configuration was already set to the value you suggested. I tried around with some values, but none worked. I set it to automatic, and it seems to use the value that has the described problem.

This could be a compositor setting (similar to “unredirect full screen windows”). Check the settings for your DE (whatever that is) or whatever settings you have manually configured (e.g. “full compositor pipeline” etc.).

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That sounds promising. Although I have no understanding what the settings mean (I’m using Plasma), I tried tinkering with the output module (it was set to OpenGL 2.0 before), and using XRender it doesn’t seem to happen anymore. OpenGL 3.1 didn’t change anything. Could that be a problem of hardware acceleration? Does that have significant other side effects?

I think setting up the outputs with xrandr is the way to go.

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