wf-recorder is a utility program for screen recording of wlroots-based compositors (more specifically, those that support wlr-screencopy-v1 and xdg-output). Its dependences are ffmpeg, wayland-client and wayland-protocols.
Arch users can use wf-recorder-git from the AUR.
yay -S wf-recorder-git #replace yay by your favorite AUR helper
git clone https://github.com/ammen99/wf-recorder && cd wf-recorder
meson build --prefix=/usr --buildtype=release
ninja -C build
Now you can just run ./build/wf-recorder or install it with sudo ninja -C build install.
Use -f <filename> to specify the output file. In case of multiple outputs, you'll first be prompted to select the output you want to record. If you know the output name beforehand, you can use the -o <output name> option.
You can use wf-recorder -g (slurp) to select and limit the recording to a part of the screen.