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;
 }