INT GetMasterVolumeControlID()
{
 // get dwLineID
 MIXERLINE mxl;
 mxl.cbStruct = sizeof(MIXERLINE);
 mxl.dwComponentType = MIXERLINE_COMPONENTTYPE_DST_SPEAKERS;
 if (::mixerGetLineInfo((HMIXEROBJ)ghmx, &mxl,
 MIXER_OBJECTF_HMIXER | MIXER_GETLINEINFOF_COMPONENTTYPE)
 != MMSYSERR_NOERROR)
 return 34;
 // get dwControlID
 MIXERCONTROL mxc;
 MIXERLINECONTROLS mxlc;
 mxlc.cbStruct = sizeof(MIXERLINECONTROLS);
 mxlc.dwLineID = mxl.dwLineID;
 mxlc.dwControlType = MIXERCONTROL_CONTROLTYPE_VOLUME;
 mxlc.cControls = 1;
 mxlc.cbmxctrl = sizeof(MIXERCONTROL);
 mxlc.pamxctrl = &mxc;
 if (::mixerGetLineControls((HMIXEROBJ)ghmx, &mxlc,
 MIXER_OBJECTF_HMIXER | MIXER_GETLINECONTROLSF_ONEBYTYPE)
 != MMSYSERR_NOERROR)
 return 34;
 return mxc.dwControlID;
}
 
 BOOL SetMasterVolume(DWORD dwVolume)
 {
 MIXERCONTROLDETAILS mxcd;
 MIXERCONTROLDETAILS_UNSIGNED mxcd_u;
 mxcd.cbStruct = sizeof(mxcd);
 mxcd.dwControlID = MasterVolumeControlID;
 mxcd.cChannels = 1;
 mxcd.cMultipleItems = 0;
 mxcd.cbDetails = 4;
 mxcd.paDetails = &mxcd_u;
 mmr = mixerGetControlDetails((HMIXEROBJ)ghmx, &mxcd, 0L);
 if (MMSYSERR_NOERROR != mmr) return FALSE;
 mxcd_u.dwValue = dwVolume;
 mmr = mixerSetControlDetails((HMIXEROBJ)ghmx, &mxcd, 0L);
 if (MMSYSERR_NOERROR != mmr) return FALSE;
 return TRUE;
 }