[Bug] Screen sharing not working for external monitors

[Elias-Graf]

The preview seems to work:

But as soon as I select one of the external monitors, it stops working:

Continuing anyway, leads to the website rendering a black box. The aspect ratio seems to be correct, though:

E.g.: here is a widescreen:

The website I used to test would be: https://webrtc.github.io/samples/src/content/getusermedia/getdisplaymedia/

I can produce the same or similar behavior using OBS-Studio. The red rectangle is a screen capture of my external widescreen:

if it's of any help, I'm on NixOS with the "nixos-comis" flake at revision: 4a755a6886b93fd8410782172e2356fef0eadccc.

The internal (laptop) display works both on the website, and as you can see in the screenshot above, in OBS-Studio as well.

[ids1024]

What graphics card(s) does the system have?

This is a known issue currently in some cases with multi-GPU systems (like a laptop where the external monitors are connected to a dGPU, while the builtin monitor is connected to the iGPU).

If the system has only one GPU, though, I'm not aware of what's causing it.

[murilosr]

I'm having the same problem. Using PopOS 24.04 with COSMIC/Wayland. The external screen capture appears only black on OBS Studio, while the laptop builtin screen works with the screen capture.

My laptop have the Intel UHD Graphics and a NVIDIA GTX 1650 Mobile.

If I use the "Run with NVIDIA..." option, when I select the screen, the system crashes and COSMIC restarts with everything closed (I don't know how to capture logs from this).

If you have any idea how to debug it to help with fix, tell me.

PS: I installed PopOS 24 today, so I don't know if it was working before. On PopOS 22 (GNOME) it works perfectly with both screens.

[Elias-Graf]

Yes indeed, my system has two GPUs installed. Can you link me the tracking issue? I am very interested in seeing this fixed. Sharing external monitors is quite useful in a professional environment :)

Here is my neofetch output:

          ▜███▙       ▜███▙  ▟███▛             --------------
           ▜███▙       ▜███▙▟███▛              OS: NixOS 25.05 (Warbler) x86_64
            ▜███▙       ▜██████▛               Host: 82WM (Legion Pro 5 16ARX8)
     ▟█████████████████▙ ▜████▛     ▟▙         Kernel: Linux 6.12.28
    ▟███████████████████▙ ▜███▙    ▟██▙        Uptime: 1 min
           ▄▄▄▄▖           ▜███▙  ▟███▛        Packages: 1357 (nix-system), 978 (nix-user)
          ▟███▛             ▜██▛ ▟███▛         Shell: zsh 5.9
         ▟███▛               ▜▛ ▟███▛          Display (TMA2038): 2560x1600 @ 240 Hz (as 2048x1280) in 16" [Built-in]
▟███████████▛                  ▟██████████▙    DE: COSMIC
▜██████████▛                  ▟███████████▛    WM: cosmic-comp (Wayland)
      ▟███▛ ▟▙               ▟███▛             Cursor: Posy-Improved (32px)
     ▟███▛ ▟██▙             ▟███▛              Terminal: .cosmic-term-wr
    ▟███▛  ▜███▙           ▝▀▀▀▀               CPU: AMD Ryzen 9 7945HX (32) @ 5.46 GHz
    ▜██▛    ▜███▙ ▜██████████████████▛         GPU 1: NVIDIA GeForce RTX 4070 Max-Q / Mobile [Discrete]
     ▜▛     ▟████▙ ▜████████████████▛          GPU 2: AMD Radeon 610M [Integrated]
           ▟██████▙       ▜███▙                Memory: 3.19 GiB / 61.98 GiB (5%)
          ▟███▛▜███▙       ▜███▙               Swap: 0 B / 8.00 GiB (0%)
         ▟███▛  ▜███▙       ▜███▙              Disk (/): 320.95 GiB / 525.62 GiB (61%) - ext4
         ▝▀▀▀    ▀▀▀▀▘       ▀▀▀▘              Local IP (wlo1): 192.168.0.207/24
                                               Battery (L22D4PC0): 65% [Charging, AC Connected]
                                               Locale: en_US.UTF-8

[ids1024]

#76 should fix some issues involving multi-GPU capture. There are still some things to improve though.