|Developer(s)||Lennart Poettering, Pierre Ossman, Shahms E. King, Tanu Kaskinen, Colin Guthrie|
|Initial release||July 2004|
|Stable release||5.0 / 4 March 2014|
|Operating system||FreeBSD, NetBSD, OpenBSD, Linux, Solaris, and Microsoft Windows|
|Platform||ARM, PowerPC, x86 / IA-32, x86-64, and MIPS architecture|
|License||GNU Lesser General Public License 2.1.|
PulseAudio is a sound server, a background process accepting sound input from one or more sources (processes or capture devices) and redirecting it to one or more sinks (sound cards, remote network PulseAudio servers, or other processes).
One of the goals of PulseAudio is to reroute all sound streams through it, including those from processes that attempt to directly access the hardware (like legacy OSS applications). PulseAudio achieves this by providing adapters to applications using other audio systems, like aRts and ESD.
In a typical installation scenario under Linux, the user configures ALSA to use a virtual device provided by PulseAudio. Thus, applications using ALSA will output sound to PulseAudio, which then uses ALSA itself to access the real sound card. PulseAudio also provides its own native interface to applications that want to support PulseAudio directly, as well as a legacy interface for ESD applications, making it suitable as a drop-in replacement for ESD.
For OSS applications, PulseAudio provides the
padsp utility, which replaces device files such as
/dev/dsp, tricking the applications into believing that they have exclusive control over the sound card. In reality, their output is rerouted through PulseAudio.
Few programs cannot communicate with PulseAudio:
Sound source ⟶ libALSA ⟶ PulseAudio ⟶ ALSA driver ⟶ hardware
Sound source ⟶ PulseAudio ⟶ ALSA driver ⟶ Hardware
PulseAudio is network capable:
Sound source ⟶ PulseAudio ⟶ network ⟶ PulseAudio ⟶ ALSA driver ⟶ hardware
A program can circumvent PulseAudio and communicate directly with the soundcard driver:
Sound source ⟶ ALSA driver ⟶ Hardware
A program can circumvent PulseAudio and communicate with the ALSA soundserver
Sound source ⟶ libALSA ⟶ ALSA driver ⟶ hardware
libcanberra complies with the XDG Sound Theme and Naming Specifications. libcanberra is an abstract API for desktop event sounds and a total replacement for the "PulseAudio sample cache API"
- libcanberra defines a simple abstract interface for playing event sounds.
- interfaces with ALSA through libasound.
- libcanberra has a back-end to PulseAudio.
libsydney is a total replacement for the "PulseAudio streaming API".
The main PulseAudio features include:
- Per-application volume controls
- An extensible plugin architecture with support for loadable modules
- Compatibility with many popular audio applications
- Support for multiple audio sources and sinks
- Low-latency operation and latency measurement
- A zero-copy memory architecture for processor resource efficiency
- Ability to discover other computers using PulseAudio on the local network and play sound through their speakers directly
- Ability to change which output device an application plays sound through while the application is playing sound (without the application needing to support this, and indeed without even being aware that this happened)
- A command-line interface with scripting capabilities
- A sound daemon with command line reconfiguration capabilities
- Built-in sample conversion and resampling capabilities
- The ability to combine multiple sound cards into one
- The ability to synchronize multiple playback streams
- Bluetooth audio devices with dynamic detection
- The ability to enable system wide equalization
PulseAudio is available in recent versions of several major linux distributions such as Fedora, Ubuntu, Debian, Mageia, Mandriva, Linux Mint, openSUSE, and OpenWrt. There is support for PulseAudio in the GNOME project, and also in KDE, as it is integrated into Plasma Workspaces, adding support to Phonon (the KDE multimedia framework) and KMix (the integrated mixer application) as well as a "Speaker Setup" GUI to aid the configuration of multi-channel speakers.
Problems during adoption phase
- When first adopted by distributions, PulseAudio developer Lennart Poettering described it as "the software that currently breaks your audio". Poettering later claimed that "Ubuntu didn't exactly do a stellar job. They didn't do their homework" in adopting PulseAudio for Ubuntu "Hardy Heron" (8.04), a problem which was then improved with subsequent Ubuntu releases. However, in October 2009, Poettering reported that he was still not happy with Ubuntu's integration of PulseAudio.
- Interaction with old sound components by particular software: Certain programs, such as Adobe Flash for Linux, caused instability in PulseAudio. Newer implementations of Flash plugins do not require the conflicting elements, and as a result Flash and PulseAudio are now compatible.
- Early management of buffer over-underruns: Earlier versions of Pulseaudio sometimes started to distort the processed audio due to incorrect handling of buffer over-/underruns.
Other sound servers
JACK is a professional sound server, which provides real-time, low latency (i.e. 5 milliseconds or less) audio performance and, since JACK2, supports efficient load balancing by utilizing symmetric multiprocessing, that is the load of all audio clients can be distributed among several processors. JACK is the preferred sound server for professional audio applications such as Ardour, Rezound, and LinuxSampler and multiple free audio production distributions use it as the default audio server.
It is possible for JACK and PulseAudio to coexist: while JACK is running, PulseAudio can automatically connect itself as a JACK client, allowing PulseAudio clients to make and record sound as the same time as JACK clients. The procedure is explained here.
General audio infrastructures
Before JACK and PulseAudio, sound on free systems was managed by multi-purpose integrated audio solutions. These solutions do not fully cover the mixing and sound streaming process, but they are still used by JACK and PulseAudio to send the final audio stream to the sound card.
- ALSA provides a software mixer called dmix, which was developed prior to PulseAudio. This is available on almost all Linux distributions and is a simpler PCM audio mixing solution. It does not provide the advanced features (such as timer-based scheduling, and network audio) of PulseAudio. On the other hand, ALSA offers, when combined with corresponding sound cards and software, low latencies.
- OSS. This was the original sound system used in Linux and other Unices, but was deprecated after the 2.5 Linux kernel. Proprietary development was continued by 4Front Technologies, who in July 2007 released sources for OSS under CDDL for OpenSolaris and GPL for Linux. The modern implementation, Open Sound System v4, provides software mixing, resampling, and changing of the volume on a per-application basis; in contrast to PulseAudio, these features are implemented within the kernel.
- JACK Audio Connection Kit – prevailing sound server for professional audio production
- Advanced Linux Sound Architecture – prevailing sound framework in the Linux kernel
- List of Linux audio software and List of free software for audio
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