PulseAudio

Infobox Software
name = Pulseaudio



caption = PulseAudio Device Chooser (padevchooser), the main GUI for PulseAudio.
collapsible =
author =
developer =
released =
latest release version = 0.9.13
latest release date = release date and age|2008|10|06
latest preview version =
latest preview date =
frequently updated =
programming language = C
operating system = Cross-platform
platform =
language =
status =
genre = Sound server
license = GNU General Public License,
GNU Lesser General Public License
website = [http://pulseaudio.org/ pulseaudio.org]

PulseAudio (formerly PolypAudio) is a cross-platform, networked sound server project. It is intended to be an improved drop-in replacement for the Enlightened Sound Daemon (ESD).

PulseAudio runs under Microsoft Windows and POSIX-compliant systems like Linux. Released under the terms of the GNU Lesser General Public License (for the software library portion) and the GNU General Public License (for the sound server itself), PulseAudio is free software.

Features

The main PulseAudio features include:

* Per-application volume controls [ [http://fedoraproject.org/wiki/Interviews/LennartPoettering Interviews/LennartPoettering - FedoraProject ] ]
* 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 support for latency measurement [ [http://www.digitalprosound.com/Htm/Articles/April/Audio_Latency.htm Audio latency: A long overdue discussion of the latency issue(s) ] ]
* 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

Operation

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 substitutes 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.

Alternatives

ALSA provides a software mixer called dmix, which was developed prior to PulseAudio and imposes less overhead. However, it does not provide any of the advanced features of PulseAudio, such as re-sampling, aggregating multiple sound cards into one and network audio. While these abilities are not typically used by common users, PulseAudio can also interoperate with legacy sound systems, including those that were designed to exclusively lock the sound card. This achieves more complete redirection of audio streams into the mixer.

Moverover ALSA's dmix is very hard to set up correctly and is not on by default on most installations and even getting multiple sources to give output to the same sink, which is the main purpose of dmix, is often never achieved.

See also

* JACK Audio Connection Kit
* aRts
* List of Linux audio software

References

External links

* [http://pulseaudio.org/ Official website]
* [http://pulseaudio.org/wiki/PerfectSetup Perfect setup]
* [http://0pointer.de/blog/projects/pulse.html The Project Formerly Known as Polypaudio] , a blog entry by one of the PulseAudio developers discussing the name change