Discussion of the API is done via the openal-devel mailing list.
This is the OpenAL Utility Toolkit (ALUT) Reference Manual.
Some previous versions of ALUT were released under the BSD license - others under LGPL. This version will be released exclusively under LGPL.
At the time of the first writing of this document (August 2005), ALUT was a set of undocumented semi-portable functions that were mixed up in the OpenAL library distribution. The intent had always been that ALUT would be a cleanly separated library that would be portable between systems. It was hoped that it would be well suited to producing succinct demo programs and to help new developers to get started with OpenAL. It was to do this by removing the annoying details of getting an audio application started - allowing developers to learn OpenAL without distractions such as loading sound samples from disk.
In order to move from this initial implementation to a clean API that would meet the original goals of ALUT, it was necessary to break from the past and make a clean start. The original version(s) were unnumbered - so we will arbitarily label all previous versions as 0.x.x and start this cleaned up version at release 1.0.0 to reflect changed API and implementations.
There are no formal guarantees of reverse compatibility with the various versions of ALUT prior to 1.0.0. Having said that, some effort has been made to at least allow these programs to continue to run if they are recompiled against ALUT 1.0.0 or later.
The old Linux implementation of OpenAL poses a special compatibility problem: ALUT 0.x.x was not a physically separate library on this platform, it was actually part of libopenal itself. This is bad for at least two reasons: It was handled differently on other platforms and much more seriously it locked together OpenAL and ALUT releases. So a deliberate decision was made to break binary compatibility in this respect and cleanly split the libraries into an OpenAL (i.e. AL and ALC) part and an ALUT one.
If you have a program which needs such an old, deprecated "combined OpenAL/ALUT" and you are not able to recompile it for some reason (e.g. it is available in binary format only), then temporarily setting the environment variable LD_PRELOAD to the full path of your installed ALUT dynamic library can help. If this really works depends on the platform, but e.g. Linux, FreeBSD, NetBSD, Solaris etc. support this mechanism. On Mac OS X there is a similar environment variable called DYLD_INSERT_LIBRARIES, but this has not been tested yet.
Let's assume that your ALUT dynamic library is at the usual location /usr/lib/libalut.so and you have an old program called myOldProg, then the following commandline in Bash syntax does the trick:
LD_PRELOAD="/usr/lib/libalut.so" myOldProg
Note that setting LD_PRELOAD globally might not be a good idea, because in that case the new ALUT would be loaded before every dynamically linked executable.
If you are already familiar with OpenGL and its utility toolkit GLUT, then you should feel very familiar with ALUT. Wherever GLUT has 'GL', ALUT has 'AL' and wherever GLUT has 'glut', ALUT has 'alut'. 'Window' is replaced with 'Context' throughout the API.
Here is the traditional first program for any language or library, but this time it is actually saying 'Hello, world!' instead of printing it:
#include <stdlib.h>
#include <AL/alut.h>
int
main (int argc, char **argv)
{
ALuint helloBuffer, helloSource;
alutInit (&argc, argv);
helloBuffer = alutCreateBufferHelloWorld ();
alGenSources (1, &helloSource);
alSourcei (helloSource, AL_BUFFER, helloBuffer);
alSourcePlay (helloSource);
alutSleep (1);
alutExit ();
return EXIT_SUCCESS;
}
Note that there error checks are missing in the program above to keep it simple.
All ALUT programs should contain:
#include <AL/alut.h>
The ALUT header includes <AL/al.h> and <AL/alc.h> for you so you don't need to include them again - although it does not hurt to do so. ALUT reserves the "ALUT_" prefix for preprocessor macros, so you should never define such a macro in your own program. Furthermore, you should not rely on any macro starting with "ALUT_" not mentioned in this specification.
If you are using the freealut implementation of ALUT, which is available via the OpenAL homepage, you can find out the necessary compilation flags by using one of the following commands:
pkg-config --cflags freealut freealut-config --cflags
To find out the necessary flags for linking, use one of the following commands:
pkg-config --libs freealut freealut-config --libs
On Windows, link with alut.dll and openal32.dll.
ALUT reserves the "alut" prefix for globally visible functions and variables, so you should never define such a function or variable in your own program. Furthermore, you should not rely on any such function or variable not mentioned in this specification.
ALUT's error handling and reporting is a little bit different from the one used in OpenAL and OpenGL: All functions which can fail report success/failure via a return value, where AL_FALSE / AL_NONE / NULL mean failure. alutGetError can be used to find out what exactly went wrong.
It is guaranteed that if a function fails, no data pointed to by pointer arguments has been changed.
alutGetError - return and clear the current error state
ALenum alutGetError (void);
Any ALUT routine that fails will return AL_FALSE / AL_NONE / NULL and set the global error state. If a subsequent error occurs while there is still an error recorded internally, the second error will simply be ignored. Calling alutGetError will reset the error code to ALUT_ERROR_NO_ERROR. Note that the error state is not cleared by other successful ALUT calls.
alutGetError returns the contents of the global error state, which can be one of the following values:
alutGetError can be called in any ALUT state and will never fail.
alutGetErrorString - return an error message string given an error code
const char *alutGetErrorString (ALenum error);
alutGetErrorString can be used to convert an error code into a human-readable description. The precise text of these descriptions may vary from implementation to implementation and should not be relied upon by the application.
alutGetErrorString returns a pointer to an immutable zero-terminated string corresponding to the given error code.
alutGetErrorString can be called in any ALUT state and will never fail. An unknown error code is not considered an error and a generic description will be returned in that case.
A typical ALUT program might look like this:
static void
reportError (void)
{
fprintf (stderr, "ALUT error: %s\n",
alutGetErrorString (alutGetError ()));
exit (EXIT_FAILURE);
}
int
main (int argc, char **argv)
{
if (!alutInit (&argc, argv))
{
reportError ();
}
/* ...play audio for a while... */
if (!alutExit ())
{
reportError ();
}
return EXIT_SUCCESS;
}
ALUT starts in an uninitialized state. alutInit and alutInitWithoutContext put ALUT into the initialized state. Those functions must only be called when the state is uninitialized. alutExit puts ALUT back from an initialized state to an uninitialized one.
The following functions must only be called in an initialized state and with a current context: alutExit, alutCreateBufferFromFile, alutCreateBufferFromFileImage, alutLoadMemoryFromFile, alutLoadMemoryFromFileImage, alutGetMIMETypes, alutCreateBufferHelloWorld, alutCreateBufferWaveform. All these functions check for AL/ALC errors on entry and immediately return ALUT_ERROR_AL_ERROR_ON_ENTRY or ALUT_ERROR_ALC_ERROR_ON_ENTRY if there was one. Note that as a consequence of these checks the AL/ALC error states for the current context/device are cleared after calling any of these functions.
alutSleep can be called in every state.
The following functions never fail and can be called in any state: alutGetError, alutGetErrorString, alutGetMajorVersion, alutGetMinorVersion.
alutInit - initialize the ALUT library and create a default current context
ALboolean alutInit (int *argcp, char **argv);
alutInit initializes the ALUT internals and creates an OpenAL context on the default device and makes it the current OpenAL context. If you want something more complex than that (e.g. running on a non-default device or opening multiple contexts on multiple devices), you can use alutInitWithoutContext instead. alutInit examines the commandline arguments passed to it and remove those it recognizes. It is acceptable to pass two NULL pointers in settings where no useful information can be obtained from argc and argv.
alutInit returns AL_TRUE on success or AL_FALSE on failure.
If you pass alutInit the argc and argv from your main program, it will examine your command-line options and use (and remove) those options that it recognises:
int
main (int argc, char **argv)
{
alutInit (&argc, argv);
...
}
Precisely which (if any) command-line options are accepted and what they control is implementation and operating system dependent. Note that some implementations will use argv[0] in debug and error messages - but this is not guaranteed by the API because it is operating-system dependent. On some OS's, alutInit may use initial settings from other sources such as 'registry' data, '.alutrc' files or shell variables. Please consult the README.xxx file for your OS if you need further details.
alutInitWithoutContext - initialize the ALUT library
ALboolean alutInitWithoutContext (int *argcp, char **argv);
alutInitWithoutContext initializes the ALUT internals. It does not create any OpenAL context or device, so this has to be done via the usual ALC calls. alutInitWithoutContext examines the commandline arguments passed to it and remove those it recognizes. It is acceptable to pass two NULL pointers in settings where no useful information can be obtained from argc and argv.
alutInitWithoutContext returns AL_TRUE on success or AL_FALSE on failure.
alutExit - shutdown the ALUT library
ALboolean alutExit (void);
When the application has finished playing audio, it should shut down ALUT using aluExit. This closes any OpenAL device/context that ALUT may have created in alutInit (but not any that the application created using ALC). After calling alutExit, you may subsequently call alutInit or alutInitWithoutContext again. Note that under well-behaved operating systems, it should be acceptable to simply exit from your program without bothering to call alutExit, relying on the OS to clean up after you. However, it is dangerous to rely on this behavior if portable operation is expected.
alutExit returns AL_TRUE on success or AL_FALSE on failure.
ALUT attempts to simplify the business of getting a simple application running by providing loaders for a range of file formats. Rather than enumerate a list of formats that will likely grow with time, the loaders are generic and try to do their best either by using OpenAL extensions if possible or by converting the sound data into standard OpenAL formats.
In order to simplify initial startup and to keep test program distributions clean, ALUT provides built-in sounds, too, that do not require disk I/O because they are built into the ALUT library. These functions may be used to write compact ALUT test/example applications with no external file dependancies whatsoever. When sending short application programs to either the ALUT or OpenAL developers as a part of bug reporting, one should endeavor to use these functions instead of loading ones own sound files.
There are eight (= 4 * 2) different loaders, corresponding to the sources and destinations of the sound data. The possible sources are:
The possible destinations are:
alutCreateBufferFromFile - load a sound file into an OpenAL buffer
ALuint alutCreateBufferFromFile (const char *filename);
alutCreateBufferFromFile tries to guess the sound data format by looking at the filename and/or the file contents and loads the sound data into an OpenAL buffer.
On success, alutCreateBufferFromFile returns a handle to an OpenAL buffer containing the loaded sound. It returns AL_NONE on failure.
alutCreateBufferFromFileImage - load in-memory sound data into an OpenAL buffer
ALuint alutCreateBufferFromFileImage (const ALvoid *data, ALsizei length);
alutCreateBufferFromFileImage tries to guess the sound data format by looking at the contents of the memory region given as parameters and loads the sound data into an OpenAL buffer.
On success, alutCreateBufferFromFileImage returns a handle to an OpenAL buffer containing the loaded sound. It returns AL_NONE on failure.
alutCreateBufferHelloWorld - create a buffer with a 'Hello, world!' sound
ALuint alutCreateBufferHelloWorld (void);
alutCreateBufferHelloWorld returns a handle to an OpenAL buffer containing the sound of someone saying 'Hello, world!'.
On success, alutCreateBufferHelloWorld returns a handle to an OpenAL buffer containing a 'Hello, world!' sound. It returns AL_NONE on failure.
alutCreateBufferWaveform - create a buffer with a synthesized waveform sound
ALuint alutCreateBufferWaveform (ALenum waveshape,
ALfloat frequency,
ALfloat phase,
ALfloat duration);
alutCreateBufferWaveform returns a handle to an OpenAL buffer containing a snippet of audio with the specified waveshape at the specified frequency (in Hertz), phase (in degrees: -180 to +180) and duration (in seconds). Allowed waveforms are:
The duration will always be rounded up to an exact number of cycles of the sound to avoid a click if you loop the sample. The frequency and phase arguments are ignored for ALUT_WHITENOISE.
On success, alutCreateBufferWaveform returns a handle to an OpenAL buffer containing the synthesized waveform. It returns AL_NONE on failure.
alutLoadMemoryFromFile - load a sound file into OpenAL-like data
ALvoid *alutLoadMemoryFromFile (const char *filename,
ALenum *format,
ALsizei *size,
ALfloat *frequency);
alutLoadMemoryFromFile tries to guess the sound data format by looking at the filename and/or the file contents and loads the sound data into a newly malloced buffer, possibly converting it in the process. The format is guaranteed to be a standard OpenAL format afterwards.
On success, alutLoadMemoryFromFile returns a pointer to a newly allocated memory area containing the sound data, which can be freed if not needed anymore. It returns NULL on failure. If any of the format, size or frequency parameters are non-NULL, the respective information about the sound will be passed back.
alutLoadMemoryFromFileImage - convert in-memory sound data into OpenAL-like data
ALvoid *alutLoadMemoryFromFileImage (const ALvoid *data,
ALsizei length,
ALenum *format,
ALsizei *size,
ALfloat *frequency);
alutLoadMemoryFromFileImage tries to guess the sound data format by looking at the contents of the memory region given as the first two arguments and loads the sound data into a newly malloced buffer, possibly converting it in the process. The format is guaranteed to be a standard OpenAL format afterwards.
On success, alutLoadMemoryFromFileImage returns a pointer to a newly allocated memory area containing the sound data, which can be freed if not needed anymore. It returns NULL on failure. If any of the format, size or frequency parameters are non-NULL, the respective information about the sound will be passed back.
alutLoadMemoryHelloWorld - load a 'Hello, world!' sound into OpenAL-like data
ALvoid *alutLoadMemoryHelloWorld (ALenum *format,
ALsizei *size,
ALfloat *frequency);
alutLoadMemoryHelloWorld loads the sound of someone saying 'Hello, world!' into a newly malloced buffer. The sound data is guaranteed to be in a standard OpenAL format, with a sample frequency chosen by the ALUT implementation.
On success, alutLoadMemoryHelloWorld returns a pointer to a newly allocated memory area containing the sound data, which can be freed if not needed anymore. It returns NULL on failure. If any of the format, size or frequency parameters are non-NULL, the respective information about the sound will be passed back.
alutLoadMemoryWaveform - load a synthesized waveform sound into OpenAL-like data
ALvoid *alutLoadMemoryWaveform (ALenum waveshape,
ALfloat frequency,
ALfloat phase,
ALfloat duration,
ALenum *format,
ALsizei *size,
ALfloat *sampleFrequency);
alutLoadMemoryWaveform loads a snippet of audio with the specified waveshape at the specified frequency (in Hertz), phase (in degrees: -180 to +180) and duration (in seconds) into a newly malloced buffer. The sound data is guaranteed to be in a standard OpenAL format, with a sample frequency chosen by the ALUT implementation. Allowed waveforms are:
The duration will always be rounded up to an exact number of cycles of the sound to avoid a click if you loop the sample. The frequency and phase arguments are ignored for ALUT_WHITENOISE.
On success, alutLoadMemoryWaveform returns a pointer to a newly allocated memory area containing the sound data, which can be freed if not needed anymore. It returns NULL on failure. If any of the format, size or sample frequency parameters are non-NULL, the respective information about the sound will be passed back.
alutGetMIMETypes - get list support supported audio MIME types
const char *alutGetMIMETypes (ALenum loader);
alutGetMIMETypes returns a comma-separated list of supported MIME types for the given loader type, e.g. something like "audio/basic,audio/mpeg,audio/x-wav". Allowed loader types are:
It is possible that ALUT_LOADER_MEMORY loaders will be unable to support some file types that ALUT_LOADER_BUFFER loaders can support (although the reverse is never the case). Furthermore, it is possible that for some file types (notably audio/x-wav) the support may be only for a few sub-formats. For example, an implementation may advertise that audio/x-wav is supported when in fact it only supports uncompressed (i.e. PCM) WAV files and not any of the compressed subformats. In this event, the various ALUT loaders may return an error and set ALUT_ERROR_UNSUPPORTED_FILE_SUBTYPE rather than ALUT_ERROR_UNSUPPORTED_FILE_TYPE which would indicate that no files of this type are allowed.
On success, alutGetMIMETypes returns a zero-terminated string which contains a comma-separated list of supported MIME types. It returns NULL on failure.
For backwards-compatibility with ALUT 0.x.x, ALUT still offers the three deprecated functions below. Note that on MacOS 0.x.x version, the 'loop' parameter is omitted from both loader functions.
void alutLoadWAVFile (ALbyte *filename,
ALenum *format,
void **data,
ALsizei *size,
ALsizei *frequency,
ALboolean *loop);
void alutLoadWAVMemory (ALbyte *buffer,
ALenum *format,
void **data,
ALsizei *size,
ALsizei *frequency,
ALboolean *loop);
void alutUnloadWAV (ALenum format ALvoid *data, ALsizei size, ALsizei frequency);
ALUT version numbers consist of a major version number, a minor version number, and a patchlevel. The former two numbers will match the major/minor version number of the corresponding ALUT specification document and can be accessed at compile time as well as runtime. The patchlevel is not programmatically available and it is incremented only when fixing bugs without any API changes.
alutGetMajorVersion - return the major ALUT version number
ALint alutGetMajorVersion (void);
alutGetMajorVersion returns the major version number of the ALUT in use, which will match the major version number of the corresponding ALUT specification document.
alutGetMajorVersion returns the major version number of the ALUT in use.
alutGetMajorVersion can be called in any ALUT state and will never fail.
alutGetMinorVersion - return the minor ALUT version number
ALint alutGetMinorVersion (void);
alutGetMinorVersion returns the minor version number of the ALUT in use, which will match the minor version number of the corresponding ALUT specification document.
alutGetMinorVersion returns the minor version number of the ALUT in use.
alutGetMinorVersion can be called in any ALUT state and will never fail.
#define ALUT_API_MAJOR_VERSION 1 #define ALUT_API_MINOR_VERSION 1
Version 1.0.0 introduced the above preprocessor symbols, whose values will be incremented appropriately in future revisions of ALUT. In version 1.1.0, alutLoadMemoryHelloWorld and alutLoadMemoryWaveform have been added to the ALUT API.
Applications can verify at runtime that they have been compiled and linked with the matching header file and library file as follows:
#ifdef ALUT_API_MAJOR_VERSION
if (alutGetMajorVersion () != ALUT_API_MAJOR_VERSION ||
alutGetMinorVersion () != ALUT_API_MINOR_VERSION)
/* Oh-oh! The ALUT header and the ALUT library are different revisions... */
#else
/* Oh-oh! We're linking against an ALUT 0.x.x header file... */
#endif
Having a general utility function like the following in an audio-related toolkit might seem strange at first, but sleeping is a common task in a lot of audio demos and it can't be done portably without cluttering the source code with #ifdefs.
alutSleep - sleep for a given number of seconds
ALboolean alutSleep (ALfloat duration);
alutSleep will delay the execution of the current thread for at least the given amount of seconds. It will only return earlier if a signal has been delivered to the thread, but this does not count as an error. Note that sleeping for zero seconds will give other runnable threads a chance to run.
alutSleep returns AL_TRUE on success or AL_FALSE on failure. Note that current implementations will always succeed if the duration is non-negative, but this might change in the future.