Technical Q&A

SND13 - The siMonitorSource Selector (12-April-98)

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'),