GNOME Screen Cast OBS Studio plugin

Small source plugin to use GNOME Screen Cast functionality as a source for OBS Studio.

GNOME Screen Cast works for all GNOME sessions regardless of the compositor being used. Basically saying that the main purpose of this plugin is to capture screens under Wayland sessions where the X11 capture falls short.

The implementation is kind of weird. Not sure if there are better ways - but the GNOME Screen Cast normally insist of writing to a file. Here we trick the system to write to a SHM socket instead which we then read and pass to OBS.

I'm not sure how latency or audio/video sync is handled by OBS. But as soon as a frame is read it gets a time stamp of os_gettime_ns() which felt like the best bet for a live source. Since I have no idea what the master clock is each frame gets a time stamp of it's frame number. OBS Studio seems smart enough to do the right thing then.

Known issues

GNOME Screen Cast seems to be limited to a single concurrent session.

The mouse cursor is currently very choppy. The reason for this is that the cursor drawing is done at the GNOME Screen Cast implementation but they only update cursor coordinates every 100ms.

Todo

Keep an eye on support for the Freedesktop variation of this API:

https://github.com/flatpak/xdg-desktop-portal/blob/master/data/org.freedesktop.portal.ScreenCast.xml

Once KDE/GNOME and distributions have picked this up we could modify the plugin slightly to have unified platform support.

Build

I don't know CMake so you will have to deal with meson instead. Assuming that all dependencies are installed correctly this should do the trick:

$ meson --buildtype=release build
$ ninja -C build

# optional; for installing the plugin into
# '/usr/local/lib/obs-plugins'

$ sudo ninja -C build install

Dependencies

On Fedora, the following dependencies may need to be installed:

• meson (to build)
• libgnome-devel (gdk-3.0)
• gstreamer1-devel gstramer1-plugins-base-devel (gstreamer-1.0)