Technical Q&As

Q How do I use the new siMonitorAvailable and siMonitorSource selectors?

A These selectors work with the sound output component to select the source that the user hears and makes that source the default recording source. Because this selector works with only with the sound output component, you don't need a sound channel to use it.

The siMonitorAvailable selector returns a SoundInfoList just like siOSTypeInputAvailable does; it is a structure to a short and a Handle. The handle contains an array of OSTypes which are the input sources that can be monitored. See Q&A SND12 for more information about working with a SoundInfoList structure.

Here is some sample code showing how to find a sound output component and use the siMonitorSource and siMonitorAvailable selectors:

include    <Sound.h>#include    <Errors.h>#include    <Memory.h>         
// A simple application that gets the available monitor sources, 
// finds each of the monitor source names,
// determines which sources are enabled, and sets various sources.
         
void main(void) {
    NumVersionVariant       smVersion;
    ComponentResult         err;
    OSType                  source;
    SoundInfoList           monitorList;
    Component               device;
    ComponentDescription    looking;
         
    smVersion.parts = SndSoundManagerVersion();
         
    // Only Sound Manager 3.1 or later implements the SoundComponentGet/SetInfo calls.
    // If you know you're going to run on System 7.5 or later, 
    // you can skip the SM version check.
         
    if (smVersion.whole >= 0x03100000) {
        looking.componentType = kSoundOutputDeviceType;
        looking.componentSubType = 0;
        looking.componentManufacturer = kAppleManufacturer;
        looking.componentFlags = 0;
        looking.componentFlagsMask = 0;
        device = FindNextComponent (0, &looking);
         
        // here's how to get a list of the available monitor sources 
        // (and tell if monitor sources are supported)
        // this returns a list of the OSTypes for the sources 
        // (don't forget to dispose of the handle later)
        
        err = GetSoundOutputInfo(device, siMonitorAvailable, &monitorList);
        
        if (err != noErr)                        // monitor sources not supported, bail in your own way
            goto Exit;
         
        DisposeHandle(monitorList.infoHandle);   // don't forget to dispose of the returned handle
         
        // find out which source is monitored
        GetSoundOutputInfo(device, siMonitorSource, &source);
         
        // set CD as the monitor source (if it is present - err <> noErr if not available)
        err = SetSoundOutputInfo(device, siMonitorSource, (void *)kCDSource);
         
        // find out which source is monitored again, to check that the setting made above worked
        err = GetSoundOutputInfo(device, siMonitorSource, &source);
    }
         
Exit:
    return;
}

The selectors are defined in Universal Headers 3.1 and later. They are:

   siMonitorAvailable            = FOUR_CHAR_CODE('mnav'),
   siMonitorSource               = FOUR_CHAR_CODE('mons'),