I have the same issue that alexmateescu mentions but it also appears to affect konsole depending on which monitor it's on.  You can also test on twitch or vimeo videos.  Full screen will "fade to black" or "become full screen with only black for the video".  The audio plays on.

I've also noticed that reducing the window of the application to not maximized will usually allow the full screen video to play.

Operating System: Arch Linux
KDE Plasma Version: 5.20.1
KDE Frameworks Version: 5.75.0
Qt Version: 5.15.1
Kernel Version: 5.9.1-arch1-1
OS Type: 64-bit
Processors: 4 × Intel® Core™ i5-4690K CPU @ 3.50GHz
Memory: 19.5 GiB of RAM
Graphics Processor: GeForce GTX 1080/PCIe/SSE2

Operating System: KDE Neon
KDE Plasma Version: 5.20.1
KDE Frameworks Version: 5.75.0
Qt Version: 5.15.0
Kernel Version: 5.4.0-52-lowlatency
OS Type: 64-bit
Processors: 8 × Intel® Core™ i7-6700K CPU @ 3.40GHz
Memory: 15.6 GiB of RAM
Graphics Processor: GeForce GTX 1070/PCIe/SSE2

(In reply to timonoj from comment #2)
> Operating System: KDE Neon
> KDE Plasma Version: 5.20.1
> KDE Frameworks Version: 5.75.0
> Qt Version: 5.15.0
> Kernel Version: 5.4.0-52-lowlatency
> OS Type: 64-bit
> Processors: 8 × Intel® Core™ i7-6700K CPU @ 3.40GHz
> Memory: 15.6 GiB of RAM
> Graphics Processor: GeForce GTX 1070/PCIe/SSE2

Sorry...I meant to say I have the same issue, but on KDE Neon, not Arch.

Can you provide a screenshot? also does disabling compositing or switching to another render backend help?

Vlad,

A screenshot isn't really going to show you anything.  Here's my own video (no audio recorded):

https://ufile.io/llauu9et

Yes, disabling compositing (Alt+Shift+F12) appears to correct this but I don't think this is a good long-term solution.  Previously I used OpenGL 2.0 rendering backend because OpenGL 3.1 would result in the rare crashing which would then have the compositor disabled going forward every reboot.  I'm currently using OpenGL 3.1 just to use a different backend in hopes it was something with OpenGL 2.0.  I haven't used XRender because if I recall correctly, it's software-based.

Tested XRender.  Fixes the issue but introduces screen tearing for videos with any real movement.  Beyond that it seems a little slower at various window transitions.  Not an optimal solution.

Ok, here goes.
Switching the backend makes the problem go away. I had it using OpenGL 3.1, moved to 2.0, XRender and back to 3.1. All worked.
With the backend set to OpenGL 3.1, I closed the browser (Firefox) and fired up Chromium. Problem was back. Switching to 2.0 made it go away again, switching back to 3.1 was still working.

Further testing: with the problem "fixed", moving the browser to the primary screen and back to the secondary, makes the problem show up again.

alexmateescu, I don't recall but it may be the compositor is only really switched after a reboot.  Nevertheless, I have done this and still have the issue as you described.  I used simple screen recorder to capture the video and for a brief moment it worked but was not a permanent fix.  Tried a second time and was able to reproduce the error again.

(In reply to kdebugs from comment #5)
> Vlad,
> 
> A screenshot isn't really going to show you anything.  Here's my own video
> (no audio recorded):
> 
> https://ufile.io/llauu9et
That's weird. Does this also happen if you play a video using VLC or MPV? what if you try to make firefox fullscreen (by pressing F11) rather than the video? Could it be some sort of content protection stuff?

This issue is resolved for me after the latest OS updates.  This may not be the case for people on other distros like KDE Neon, Kubuntu, etc.

Operating System: Arch Linux
KDE Plasma Version: 5.20.2
KDE Frameworks Version: 5.75.0
Qt Version: 5.15.1
Kernel Version: 5.9.1-arch1-1
OS Type: 64-bit
Processors: 4 × Intel® Core™ i5-4690K CPU @ 3.50GHz
Memory: 19.5 GiB of RAM
Graphics Processor: GeForce GTX 1080/PCIe/SSE2

Notice Plasma is now 5.20.2

Vlad, previously vlc didn't show this behavior full screen.  I didn't test mpv although I suspect results would be the same.  F11 (firefox full screen) was tested and had the same results if I remember correctly.

Issue still here running 5.20.2. Firefox and Chrome, F11 or full screen using the interface, makes no difference.

Also, not sure why you'd think content protection is at play, I've stating from post #1 Falkon can play full screen just fine.

This is still an issue and maybe it was even when I thought it was taken care of.  If I start Firefox on the main monitor and full screen there are no issues.  If I move Firefox to the secondary monitor and full screen the same issue exists.  If I then move Firefox back to the primary monitor that was previously working, the issue is now also on the primary monitor.

Operating System: Arch Linux
KDE Plasma Version: 5.20.2
KDE Frameworks Version: 5.75.0
Qt Version: 5.15.1
Kernel Version: 5.9.2-arch1-1

Kernel updated.  Nvidia proprietary driver updates since October 18th:

[2020-10-18T15:27:17-0400] [ALPM] upgraded nvidia (455.28-4 -> 455.28-7)
[2020-10-30T10:34:02-0400] [ALPM] upgraded nvidia (455.28-7 -> 455.28-8)
[2020-10-31T06:25:14-0400] [ALPM] upgraded nvidia-utils (455.28-1 -> 455.38-1)
[2020-10-31T06:25:14-0400] [ALPM-SCRIPTLET] If you run into trouble with CUDA not being available, run nvidia-modprobe first.
[2020-10-31T06:25:15-0400] [ALPM] upgraded lib32-nvidia-utils (455.28-1 -> 455.38-1)
[2020-10-31T06:25:15-0400] [ALPM] upgraded nvidia (455.28-8 -> 455.38-1)

Can you try disabling the fullscreen effect?

"Full screen" in my posts generally refers to the video player embedded within a website such as youtube.  Represented by the four corners of a square or rectangle in the lower right of a youtube embedded video.  However, making Firefox itself full screen (F11) also causes the black screen issue.

Alex, do you use Synergy by chance?

I don't even know what Synergy is, so probably not.
Also what is "full screen effect"?

Are you guys having a hard time reproducing this? Because I see the issue is not even confirmed yet. Anything else I can test to help out?

Alex, I'm not part of the KDE team.  My email is an alias used to help me track things in my own inbox.  Synergy is a KM (keyboard/mouse) screen sharing solution.  You can use the hardware of one machine to control all other machines in realtime.  This is in some ways superior to remote desktop or ssh.  Synergy is known to be buggy and why I asked if you used it.  I use it for working on both the personal desktop and work laptop.

https://alternativeto.net/software/synergy/

Read the reviews if you have further interest.

Full screen usually means full screen for an application, I'm mainly talking about the embedded video player such as youtube, twitch, vimeo, etc.

Still an issue.  Firefox loaded on the left screen maximized, set the embedded video player to max/full screen and it was fine.  Moved Firefox to what I think of as the primary monitor (on the right) and the issue is still here.  Updated plasma below.

One other thing of note, why do applications not remember the last monitor they were on?  Alternatively, have any application default to a particular monitor.

Operating System: Arch Linux
KDE Plasma Version: 5.20.3
KDE Frameworks Version: 5.75.0
Qt Version: 5.15.1
Kernel Version: 5.9.8-arch1-1

I also experience this. 
Now on the latest KDE Neon, and previously on an Arch build.
My feeling is that it has to do with the NVIDIA driver, as I observe that all the comments are from users with NVIDIA like myself.

I think that Vlad is onto something, as disabling "full screen animation" from the kde settings seems to have solved it.

Created attachment 133421 [details]
attachment-18035-0.html

I'll agree. Also KDE Neon, and also with Nvidia. Disabling fullscreen
animation did fix it.

On Wed, 18 Nov 2020 at 08:28, <bugzilla_noreply@kde.org> wrote:

> https://bugs.kde.org/show_bug.cgi?id=427920
>
> sverre.v.b@gmail.com changed:
>
>            What    |Removed                     |Added
>
> ----------------------------------------------------------------------------
>                  CC|                            |sverre.v.b@gmail.com
>
> --- Comment #20 from sverre.v.b@gmail.com ---
> I also experience this.
> Now on the latest KDE Neon, and previously on an Arch build.
> My feeling is that it has to do with the NVIDIA driver, as I observe that
> all
> the comments are from users with NVIDIA like myself.
>
> I think that Vlad is onto something, as disabling "full screen animation"
> from
> the kde settings seems to have solved it.
>
> --
> You are receiving this mail because:
> You are on the CC list for the bug.

"Full screen" can be applied to many things.  Disabling the full screen Desktop Effects works well for now.  This is a feature I didn't realize was enabled so I won't miss it.  The steps for others:

System Settings >> Workspace >> Workspace Behavior >> Desktop Effects >> Full Screen

Thank you sverre for a better workaround.

Excellent find. Not only is this an acceptable workaround, it probably helps a lot pinpointing the problem. If someone was looking at it, that is.

I can't take credit for it though, Vlad was the first to mention it in this thread, and I originally found the tip on a Reddit:-)

Let's hope that someone can use the info to solve the problem properly!

With respect to Vlad, it was never obvious he was referring to the KDE settings so far as I can tell.

Okay, weird. Can you reduce the animation speed in system settings (it's in Workspace Behavior KCM) and check if the same issue occurs when a window is maximized?

Hello, i would like to add, 
this bug only occurs on the non-primary monitor : 
if i switch the monitor on which it bugs to primary, then it bugs on the now non-primary monitor, and works well on the now primary one.

Also yes, this occurs only with the compositor's full screen effect turned on.

But most importantly, i noticed that it only bugs if the window is first maximized, and then turned fullscreen. 
It doesn't happen if the window was not maximimized and then turned fullscreen.
Hope this pinpoints the problem even more! Thanks

Okay so I've pinpointed the problem a little bit more. 
After reading the source at 

https://invent.kde.org/plasma/kwin/-/blob/master/effects/fullscreen/package/contents/code/fullscreen.js 

I figured the problem was not because of primary or secondary screens, or because of maximized or unmaximized. Actually the script checks if there is a resize, and if the window was already the size of the screen (such as when it's maximized when and there's no pannel on your screen), then it bugs because of a fade-to-black.

So i'd suggest the easy temporary ""fix"" of making an app pannel on your second monitor as well. Won't work for everyone's workflow but still better than nothing.

btw doesn't occur if the compositor doesn't use opengl, and i also have a nvidia card, so it has something to do with the fade effect on these specific drivers

I have panels on both monitors, but they are on auto hide, therefore I experience the issue on both monitors. So for that alternative fix to work you have to enable always show on the panels..

(In reply to lcubeddu from comment #27)
> Hello, i would like to add, 
> this bug only occurs on the non-primary monitor : 
> if i switch the monitor on which it bugs to primary, then it bugs on the now
> non-primary monitor, and works well on the now primary one.
> 
> Also yes, this occurs only with the compositor's full screen effect turned
> on.
> 
> But most importantly, i noticed that it only bugs if the window is first
> maximized, and then turned fullscreen. 
> It doesn't happen if the window was not maximimized and then turned
> fullscreen.
> Hope this pinpoints the problem even more! Thanks

I've tried this, but still no luck reproducing the bug.

(In reply to Vlad Zahorodnii from comment #30)
> (In reply to lcubeddu from comment #27)
> > Hello, i would like to add, 
> > this bug only occurs on the non-primary monitor : 
> > if i switch the monitor on which it bugs to primary, then it bugs on the now
> > non-primary monitor, and works well on the now primary one.
> > 
> > Also yes, this occurs only with the compositor's full screen effect turned
> > on.
> > 
> > But most importantly, i noticed that it only bugs if the window is first
> > maximized, and then turned fullscreen. 
> > It doesn't happen if the window was not maximimized and then turned
> > fullscreen.
> > Hope this pinpoints the problem even more! Thanks
> 
> I've tried this, but still no luck reproducing the bug.

Which variables have you looked at?
Besides the Nvidia GPU and the requirement for an OpenGL 3.1 compositor, I can point out my monitors do not use the same aspect ratio. My primary is 16:9, but the secondary is 16:10.
Let's try to find out where our setups are different.

Alex,

I also use two Dell U2415s (16:10 aspect ratio).  Not sure about the others here.

I have experienced the same issue with Plasma 5.21.3 on Fedora 33.  Can confirm disabling fullscreen desktop effects resolves the issue. I am using HDMI out to a monitor attached to my laptop at 16:9.  The laptop screen is disabled in Display Settings and only the HDMI monitor is selected and is primary.  I am using NVidia drivers and the Compositor is set to use OpenGL 3.1.  


The issue is very reproducible for me.  The steps below will reproduce for any browser, including Chromium.

1.  Open Firefox.
2.  Maximize Firefox to fullscreen.
3.  Navigate to YouTube.
4.  Click on any YouTube video.
5.  Press play on the YouTube video.
6.  Press the fullscreen button on the YouTube video.
7.  The whole screen is now black.
8.  Press ESC to recover.

Hi, I'd like to reiterate what I've already said in this thread, since the new responses don't seem to have noticed.

The bug only happens if the window you turn into fullscreen was previously maximised at the SAME RESOLUTION than your screen. (example: if your monitor is 600x600 px, if the window is maximised at 600*599px, it won't happen, if the window is maximised at 600*600px, it will happen)

So it means that it only occurs if you don't have a task bar ! (like for example, on secondary monitors)

Hope it pinpoints the issue a little bit more!

*** Bug 435178 has been marked as a duplicate of this bug. ***

I also experience this bug in Version 5.22.5

I can confirm that it is a problem with fullscreen windows, as my panel is usually set on auto-hide.
If I set it to "always visible", the fullscreen mode of applications such as firefox (including fullscreen videos) is working again.

When the problem occurs:
- Using OpenGL 3.1 or 2.0 does not change anything.
- Using XRender fixes the problem.
- Disabling the fullscreen effect also does not change anything for me.

Operating System: Arch Linux
KDE Plasma Version: 5.22.5
KDE Frameworks Version: 5.85.0
Qt Version: 5.15.2
Kernel Version: 5.10.61-1-lts (64-bit)
Graphics Platform: X11
Graphics Processor: NVIDIA

(In reply to tobias from comment #36)
> I also experience this bug in Version 5.22.5
> 
> I can confirm that it is a problem with fullscreen windows, as my panel is
> usually set on auto-hide.
> If I set it to "always visible", the fullscreen mode of applications such as
> firefox (including fullscreen videos) is working again.
> 
> When the problem occurs:
> - Using OpenGL 3.1 or 2.0 does not change anything.
> - Using XRender fixes the problem.
> - Disabling the fullscreen effect also does not change anything for me.
> 
> Operating System: Arch Linux
> KDE Plasma Version: 5.22.5
> KDE Frameworks Version: 5.85.0
> Qt Version: 5.15.2
> Kernel Version: 5.10.61-1-lts (64-bit)
> Graphics Platform: X11
> Graphics Processor: NVIDIA
I think you are experiencing something slightly different: Bug 441904. Please add relevant information to that bug report. Thanks!

Also getting this on my second monitor. Arch Linux, Plasma 5.22.5, NVIDIA 470.63.01.

Same thing - have youtube open in Firefox, if Firefox is maximized on my second screen (non primary, no panels), then going full screen causes a black screen. Note, I have tried disabling the "full screen effect", and it is still doing this for me at least. Reducing the window size allows the video to properly go full screen.

This bug was reported against an outdated version of KWin. We have made many changes since the. 
If the issue persists in newer versions can you reopen the bug report updating the version number.

Seems to be working fine, I just retested.

On a personal note, if you guys couldn't reproduce something as simple as this, it's probably not worth my time to report further bugs.