Does OpenAL support 5.1 output on Mac OS X?

Question

I'm in the process of porting an application from Windows to Mac OS X. It is using OpenAL for handling the sound, but I'm getting a strange behavior in the initialization of the sound engine on Mac OS X (the code is running on a MacBook Pro).

Here is the code:

int InitSoundEngine(void* data[NB_BUFFERS], size_t data_size[NB_BUFFERS])
{
    ALCdevice *device;
    ALCcontext *context;
    ALenum format;
    ALuint buffers[NB_BUFFERS];

    device = alcOpenDevice(NULL);
    if (device == NULL)
        goto failed;

    context = alcCreateContext(device, NULL);
    if (context == NULL)
        goto failed;

    alcMakeContextCurrent(context);

    format = alGetEnumValue("AL_FORMAT_51CHN16");
    if (format == 0)
        goto failed;

    alGenBuffers(NB_BUFFERS, buffers);
    if (alGetError() != AL_NO_ERROR)
        goto failed;

    for (int i = 0; i < NB_BUFFERS; ++ i)
    {
        alBufferData(buffers[i], format, data[i], data_size[i], 48000);
        if (alGetError() != AL_NO_ERROR)
            goto failed;
    }

    return NO_ERROR;

 failed:
    /* Cleanup omitted for brievety */
    return INITIALIZATION_FAILED;
 }

This fails when during the call to alBufferData, with an error of AL_INVALID_VALUE. While tracing the code, we discovered that alGetEnumValue("AL_FORMAT_51CHN16") is returning 0xfffffffful, and we suspect this is the root of the issue.

The alGetEnumValue says:

ALuint alGetEnumValue(const ALchar *enumName);

Returns 0 if the enumeration can not be found, and sets an AL_INVALID_VALUE error condition. The presence of an enum value does not guarantee the applicability of an extension to the current context. A non-zero return indicates merely that the implementation is aware of the existence of this extension.

I think I use the function correctly. Is there a bug in the Mac OS X implementation of OpenAL ? Is 5.1 output supported via OpenAL on Mac OS X ? Is it supported via Core Audio (porting to Core Audio could be an option if this is true) ? Should I convert my audio from 5.1 to another format (3.1, stereo, ...) ?

Answer 1

That enum belongs to the AL_EXT_MCFORMATS extension. It is not available on Mac OS X.

Yes, CoreAudio can handle 5.1 (or any, I think) speaker setup. I don't know the details of how to feed it data though.