alsa

Advanced Linux Sound Architecture (ALSA) is the primary sound subsystem for Linux, encompassing kernel-level audio drivers and a user-space library and utilities. It provides a uniform interface to a wide range of sound hardware and supports multiple devices, channels, and sample formats. ALSA emerged to replace the legacy Open Sound System and to offer better portability, control, and low-latency performance for Linux audio applications.

At its core, ALSA consists of kernel drivers that implement the hardware interface and a user-space framework, including the libasound library and various command-line tools. The kernel side exposes audio hardware as PCM devices, controls (mixer) and timers, while the libasound API provides access to playback, capture, and control operations. Users interact with devices through applications or higher-level sound servers; software mixing and device sharing are supported via a plugin system (for example, the dmix and dsnoop plugins).

Key features include a stable PCM interface, hardware- and software-based mixing, MIDI sequencing via the snd_seq interface, and a suite of control elements for volume and routing. The ecosystem includes tools such as aplay for playback, arecord for recording, alsamixer or amixer for control, and alsactl to save and restore mixer state. ALSA libraries are widely used by Linux distributions and provide a foundation for higher-level stacks.

ALSA works alongside other sound servers such as PulseAudio and PipeWire, which can use ALSA as their low-level backend. It also provides an OSS compatibility layer (aoss) so legacy applications can use the ALSA drivers. Licensing varies: the user-space components are generally LGPL, while the kernel drivers are GPL as part of the Linux kernel.

Since its early adoption into the Linux kernel, ALSA has become the standard audio interface on most Linux systems and remains actively developed by the community.

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