mixerGetLineControls failure

I'm trying to open a mixer to monitor audio levels but am getting a MIXERR_INVALCONTROL failure on mixerGetLineControls(). Here is the code I'm using:

    MMRESULT rc;              // Return code.
    MIXERCONTROL mxc;         // Holds the mixer control data.
    MIXERLINE mxl;            // Holds the mixer line data.
    MIXERLINECONTROLS mxlc;   // Obtains the mixer control.
      MIXERCAPS mxrcaps;
      HMIXER hMixer = NULL;

      int nNumDevs = ::mixerGetNumDevs();

      ::ZeroMemory(&m_mxrcaps, sizeof(MIXERCAPS));

      if(!nNumDevs)
      {
            GetMMError(rc);
            return;
      }

      rc = ::mixerOpen(&m_hMixer, 0, 0, NULL, MIXER_OBJECTF_MIXER );
      if(rc != MMSYSERR_NOERROR )
      {
            GetMMError(rc);
            return;
      }

      if(m_hMixer == NULL)
      {
            GetMMError(rc);
            return;
      }

    // Initialize MIXERLINE structure.
    ZeroMemory(&mxl,sizeof(mxl));
    mxl.cbStruct = sizeof(mxl);

    mxl.dwComponentType = MIXERLINE_COMPONENTTYPE_DST_WAVEIN;

    rc = mixerGetLineInfo((HMIXEROBJ)m_hMixer, &mxl,
                           MIXER_GETLINEINFOF_COMPONENTTYPE);
      if(rc != MMSYSERR_NOERROR )
      {
            GetMMError(rc);
      }

    // Get the control.
    ZeroMemory(&mxlc, sizeof(mxlc));
    mxlc.cbStruct = sizeof(mxlc);
    mxlc.dwLineID = mxl.dwLineID;
    mxlc.dwControlType = MIXERCONTROL_CONTROLTYPE_PEAKMETER;
    mxlc.cControls = 1;
    mxlc.cbmxctrl = sizeof(mxc);
    mxlc.pamxctrl = &mxc;
    ZeroMemory(&mxc, sizeof(mxc));
    mxc.cbStruct = sizeof(mxc);
    rc = mixerGetLineControls((HMIXEROBJ)m_hMixer,&mxlc,
                               MIXER_GETLINECONTROLSF_ONEBYTYPE);
    if (MMSYSERR_NOERROR != rc)
      {
            GetMMError(rc);
    }

    MIXERCONTROLDETAILS mxcd;             // Gets the control values.
    MIXERCONTROLDETAILS_SIGNED volStruct; // Gets the control values.

    // Initialize the MIXERCONTROLDETAILS structure
    ZeroMemory(&mxcd, sizeof(mxcd));
    mxcd.cbStruct = sizeof(mxcd);
    mxcd.cbDetails = sizeof(volStruct);
    mxcd.dwControlID = mxc.dwControlID;
    mxcd.paDetails = &volStruct;
    mxcd.cChannels = 1;

    rc = mixerGetControlDetails((HMIXEROBJ)m_hMixer, &mxcd,
                                 MIXER_GETCONTROLDETAILSF_VALUE);
    if (MMSYSERR_NOERROR != rc)
      {
            GetMMError(rc);
      }

      ... use MIXERCONTROLDETAILS structure


Any ideas?
LVL 1
GrailmanAsked:
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chensuConnect With a Mentor Commented:
The MIXERLINE_COMPONENTTYPE_DST_WAVEIN audio line might not support the MIXERCONTROL_CONTROLTYPE_PEAKMETER control. Check out the Windows Volume Control utility and the following Win32 sample to see if the control is there.

MixApp: Sample Mixer Application
http://msdn.microsoft.com/library/devprods/vs6/visualc/vcsample/vcsmpmixapp.htm

Also, check out my article at CodeGuru.

Audio Mixer Functions Demo
http://www.codeguru.com/multimedia/ADMixer.shtml
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GrailmanAuthor Commented:
I tried your Audio Mixer Functions Demo and it worked fine but only for playing wav files. How do you use it to get the cd play or the microphone input?
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GrailmanAuthor Commented:
I tried using MIXERLINE_COMPONENTTYPE_SRC_COMPACTDISC and MIXERLINE_COMPONENTTYPE_SRC_MICROPHONE for mxl.dwComponentType but still could not get any response...?
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chensuCommented:
The controls you are trying to get are unlikely to be supported by the audio driver. Check out the Windows Volume Control utility and the following Win32 sample to see if the controls are there.
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GrailmanAuthor Commented:
The win32 sample & volume controls show the mixer so it should be there. I don't have time to dig into it for now but it looks like I should be able t find it.
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chensuCommented:
Good luck.
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