PulseAudio

PulseAudio is a free, open-source sound server for POSIX-compliant operating systems. It runs as a background daemon and acts as a proxy between audio applications and hardware devices, routing, mixing, and processing audio streams. By providing a unified API and per-application control, PulseAudio enables features such as independent volume controls, device hot-plug handling, and network streaming of audio.

Architecture and capabilities: PulseAudio uses a client-server model with a set of libraries (notably libpulse) and a modular architecture. Modules implement functionality such as ALSA compatibility, Bluetooth audio, virtual sinks and sources, and network streaming. The daemon manages multiple sinks (outputs) and sources (inputs), performs sample-rate conversion, and provides latency management and resampling as needed.

History and licensing: The project was initiated in the mid-2000s by Lennart Poettering and contributors as an alternative to existing sound servers. It is part of the freedesktop.org ecosystem and is released under the GNU Lesser General Public License. PulseAudio became the default sound server in many Linux distributions, while newer pipelines such as PipeWire have offered a different approach in recent years.

Platform support and usage: PulseAudio targets Linux and other Unix-like systems, with ports and compatibility layers for macOS and Windows available through various projects. It integrates with desktop environments such as GNOME and KDE and often works alongside ALSA and other lower-level audio subsystems. Community and distribution support remains broad, though some distributions have shifted to newer multimedia stacks.