FFmpeg
The encoder underneath nearly everything else, and a capable streamer alone.
Install
Debian, Ubuntu, Mint, Pop!_OS
sudo apt install ffmpegFedora, RHEL, Nobara
First, enable the repository:
sudo dnf install https://mirrors.rpmfusion.org/free/fedora/rpmfusion-free-release-$(rpm -E %fedora).noarch.rpmsudo dnf install ffmpegFedora ships a reduced ffmpeg-free by default; the full build with common codecs comes from RPM Fusion.
Arch, Manjaro, EndeavourOS
sudo pacman -S ffmpegopenSUSE
sudo zypper install ffmpegNixOS, or Nix on any distro
nix profile install nixpkgs#ffmpegOBS uses it, your video player uses it, and you can stream with it directly if your setup is simple enough to describe as a command.
For streamers the most common direct use is checking what your hardware can
actually encode. ffmpeg -encoders | grep -E 'nvenc|vaapi|qsv' tells you which
hardware encoders this build supports, which is the fastest way to find out
whether a missing option in OBS is a hardware problem or a packaging one.
On Fedora the distinction between ffmpeg-free and the RPM Fusion build catches
people out: the stock build omits several codecs, and the symptom is an encoder
that exists on paper but refuses to initialise.