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| OpenAL | |
|---|---|
 | |
| Original author | Loki Software |
| Developer | Creative Technology |
| Stable release | |
| Written in | C |
| Operating system | 15 operating systems See:Supported platforms |
| Type | Application programming interface |
| License |
|
| Website | www |
OpenAL (Open Audio Library[3][4]) is across-platform audioapplication programming interface (API). It is designed for efficient rendering of multichannel three-dimensional positional audio. Its API style and conventions deliberately resemble those ofOpenGL. OpenAL is an environmental3D audio library, which can add realism to a game by simulatingattenuation (degradation of sound over distance), theDoppler effect (change in frequency as a result of motion), and material densities.
OpenAL aimed to originally be anopen standard andopen-source replacement forproprietary (and generally incompatible with one another) 3D audio APIs such asDirectSound andCore Audio, though in practice has largely been implemented on various platforms as awrapper around said proprietary APIs or as a proprietary and vendor-specific fork. While thereference implementation later became proprietary and unmaintained, there are open source implementations such asOpenAL Soft available.
OpenAL was originally developed in 2000 byLoki Software to help them in their business ofportingWindows games toLinux.[5] After the demise of Loki, the project was maintained for a time by thefree software/open source community, and implemented onNVIDIA nForce sound cards and motherboards. It was hosted (and largely developed) byCreative Technology until circa 2012.
Since 1.1 (2009), the sample implementation by Creative has turned proprietary,[citation needed] with the last releases in free licenses still accessible through the project'sSubversionsource code repository. However,OpenAL Soft is a widely used open source alternative and remains actively maintained and extended.
While the OpenAL charter says that there will be an "Architecture Review Board" (ARB) modeled on the OpenGL ARB,[citation needed] no such organization has ever been formed and the OpenAL specification is generally handled and discussed via email on its public mailing list.
The original mailing list, openal-devel hosted by Creative, ran from March 2003 to circa August 2012.[6] Ryan C. Gordon, a Loki veteran who went on to developSimple DirectMedia Layer, started a new mailing list and website at OpenAL.org in January 2014.[7] As of February 2023, the list remains in use.
The general functionality of OpenAL is encoded insource objects,audio buffers and a singlelistener. A source object contains a pointer to a buffer, the velocity, position and direction of the sound, and the intensity of the sound. The listener object contains the velocity, position and direction of the listener, and the general gain applied to all sound. Buffers contain audio data inPCM format, either 8- or16-bit, in eithermonaural orstereo format. The rendering engine performs all necessary calculations for distance attenuation,Doppler effect, etc.
The net result of all of this for the end user is that in a properly written OpenAL application, sounds behave quite naturally as the user moves through the three-dimensional space of the virtual world. From a programmer's perspective, very little additional work is required to make this happen in an existing OpenGL-based 3D graphical application.
Unlike the OpenGL specification, the OpenAL specification includes two subsections of theAPI: the core consisting of the actual OpenAL function calls, and the ALC (Audio Library Context) API which is used to manage rendering contexts, resource usage and locking in a cross platform manner. There is also an 'ALUT' (Audio Library Utility Toolkit) library that provides higher level 'convenience' functions — exactly analogous to OpenGL's 'GLUT'.
In order to provide additional functionality in the future, OpenAL utilizes an extension mechanism. Individual vendors are thereby able to include their own extensions into distributions of OpenAL, commonly for the purpose of exposing additional functionality on their proprietary hardware. Extensions can be promoted to ARB (Architecture Review Board) status, indicating a standard extension which will be maintained for backwards compatibility. ARB extensions have the prospect of being added to the core API after a period of time.
For advanced digital signal processing and hardware-accelerated sound effects, the EFX (Effects Extension) orenvironmental audio extensions (EAX) can be used.
Thesingle listener model in OpenAL is tailored to a single human user and is not fit for artificial intelligence or robotic simulations or multiple human participants as in collaborative musical performances.[8]In these cases a multiple listener model is required. OpenAL also fails to take into accountsound propagation delays (thespeed of sound is used for theDoppler effect only). The distance to a sound source only translates into an amplitude effect (attenuation) and not a delay. Hence OpenAL cannot be used fortime difference of arrival calculations unless that functionality is added in separately.[9]
In order to takefull speed advantage of OpenAL, a vendor/hardware specific implementation is needed and these are seldom released as open source. Many supported platforms in fact implement OpenAL as awrapper which simply translates calls to the platform's native, and often proprietary, audio API. On Windows, if a vendor specific implementation is not detected it will fall back to the wrap_oal.dll wrapper library that translates OpenAL into DirectSound (Generic Software) or DirectSound3D (Generic Hardware); the removal of the latter fromWindows Vista onward has effectively broken generic hardware acceleration on modern versions of Windows.[10][11]
The API is available on the followingplatforms andoperating systems:[12]Android (supportsOpenSL ES),AmigaOS 3.x and 4.x,[13]Bada,BlackBerry 10,[14]BlackBerry PlayBook,BSD,iOS (supportsCore Audio),IRIX,Linux (supportsALSA,OSS,PortAudio andPulseAudio),Mac OS 8,Mac OS 9 andMac OS X (Core Audio),Microsoft Windows (supportsDirectSound,Windows Multimedia API and Windows Multimedia Device (MMDevice) API),MorphOS,OpenBSD,[15]Solaris,QNX, andAROS.[16]
Supported gaming devices are for instance:GameCube,PlayStation 2,PlayStation 3,Xbox,Xbox 360,Wii, andPlayStation Portable.
The following video games are known to use OpenAL:
{{cite web}}: CS1 maint: archived copy as title (link)Test have shown that AeonWave-OpenAL renders audio five times faster (on an AMD Athlon-64 X2 processor) and up to seven times faster (on an Intel Atom-N270 processor) than both OpenAL-Soft and OpenAL-Sample. Rendering 32 sounds on the Atom-N270 (the maximum for OpenAL-Soft) saves 1 Watt of continuous power consumption according to powertop.
Implementations:
Developer resources: