PRB: No Signal is Recorded When Using MCI or waveInxxx APIs
ID: Q159753
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The information in this article applies to:
-
Microsoft Windows Software Development Kit (SDK) 4.0
SYMPTOMS
There is no signal recorded using MCI (Media Control Interface) or
waveInXXX APIs to record through the microphone.
CAUSE
There are three possible causes:
- The microphone line is muted.
- The volume of the microphone line is turned to the minimum.
- The microphone line is not selected into the wave input destination.
RESOLUTION
You need to make sure that none of the above conditions exist in your
applications. The audio mixer API set provides a means by which each
condition can be checked and set accordingly.
MORE INFORMATION
Two input lines are involved when recording from the microphone: the
physical source line (microphone) and the logical source line (wave in).
This recording architecture can be separated into two distinct components
where the signals from the microphone source line feed into the wave in
destination line. Multiple controls influence these lines.
The first condition is cleared through a mute control. The second condition
through a volume control. To clear the third one, use a LIST control
associated with the wave input line. The following Visual C++ sample code
consists of three functions for clearing these conditions, respectively.
Although this sample is written in Visual C++, you can move the in-line
declarations up front and modify the Visual C++ style initialization to
make it a C sample:
void UnMute()
{
// Open the mixer device
HMIXER hmx;
mixerOpen(&hmx, 0, 0, 0, 0);
// Get the line info for the wave in destination line
MIXERLINE mxl;
mxl.cbStruct = sizeof(mxl);
mxl.dwComponentType = MIXERLINE_COMPONENTTYPE_DST_WAVEIN;
mixerGetLineInfo((HMIXEROBJ)hmx, &mxl, MIXER_GETLINEINFOF_COMPONENTTYPE);
// Now find the microphone source line connected to this wave in
// destination
DWORD cConnections = mxl.cConnections;
for(DWORD j=0; j<cConnections; j++){
mxl.dwSource = j;
mixerGetLineInfo((HMIXEROBJ)hmx, &mxl, MIXER_GETLINEINFOF_SOURCE);
if (MIXERLINE_COMPONENTTYPE_SRC_MICROPHONE == mxl.dwComponentType)
break;
}
// Find a mute control, if any, of the microphone line
LPMIXERCONTROL pmxctrl = (LPMIXERCONTROL)malloc(sizeof MIXERCONTROL);
MIXERLINECONTROLS mxlctrl = {sizeof mxlctrl, mxl.dwLineID,
MIXERCONTROL_CONTROLTYPE_MUTE, 1, sizeof MIXERCONTROL, pmxctrl};
if(!mixerGetLineControls((HMIXEROBJ) hmx, &mxlctrl,
MIXER_GETLINECONTROLSF_ONEBYTYPE)){
// Found, so proceed
DWORD cChannels = mxl.cChannels;
if (MIXERCONTROL_CONTROLF_UNIFORM & pmxctrl->fdwControl)
cChannels = 1;
LPMIXERCONTROLDETAILS_BOOLEAN pbool =
(LPMIXERCONTROLDETAILS_BOOLEAN) malloc(cChannels * sizeof
MIXERCONTROLDETAILS_BOOLEAN);
MIXERCONTROLDETAILS mxcd = {sizeof(mxcd), pmxctrl->dwControlID,
cChannels, (HWND)0,
sizeof MIXERCONTROLDETAILS_BOOLEAN, (LPVOID) pbool};
mixerGetControlDetails((HMIXEROBJ)hmx, &mxcd,
MIXER_SETCONTROLDETAILSF_VALUE);
// Unmute the microphone line (for both channels)
pbool[0].fValue = pbool[cChannels - 1].fValue = 0;
mixerSetControlDetails((HMIXEROBJ)hmx, &mxcd,
MIXER_SETCONTROLDETAILSF_VALUE);
free(pmxctrl);
free(pbool);
}
else
free(pmxctrl);
mixerClose(hmx);
}
void SetVolume()
{
// Open the mixer device
HMIXER hmx;
mixerOpen(&hmx, 0, 0, 0, 0);
// Get the line info for the wave in destination line
MIXERLINE mxl;
mxl.cbStruct = sizeof(mxl);
mxl.dwComponentType = MIXERLINE_COMPONENTTYPE_DST_WAVEIN;
mixerGetLineInfo((HMIXEROBJ)hmx, &mxl,
MIXER_GETLINEINFOF_COMPONENTTYPE);
// Now find the microphone source line connected to this wave in
// destination
DWORD cConnections = mxl.cConnections;
for(DWORD j=0; j<cConnections; j++){
mxl.dwSource = j;
mixerGetLineInfo((HMIXEROBJ)hmx, &mxl, MIXER_GETLINEINFOF_SOURCE);
if (MIXERLINE_COMPONENTTYPE_SRC_MICROPHONE == mxl.dwComponentType)
break;
}
// Find a volume control, if any, of the microphone line
LPMIXERCONTROL pmxctrl = (LPMIXERCONTROL)malloc(sizeof MIXERCONTROL);
MIXERLINECONTROLS mxlctrl = {sizeof mxlctrl, mxl.dwLineID,
MIXERCONTROL_CONTROLTYPE_VOLUME, 1, sizeof MIXERCONTROL, pmxctrl};
if(!mixerGetLineControls((HMIXEROBJ) hmx, &mxlctrl,
MIXER_GETLINECONTROLSF_ONEBYTYPE)){
// Found!
DWORD cChannels = mxl.cChannels;
if (MIXERCONTROL_CONTROLF_UNIFORM & pmxctrl->fdwControl)
cChannels = 1;
LPMIXERCONTROLDETAILS_UNSIGNED pUnsigned =
(LPMIXERCONTROLDETAILS_UNSIGNED)
malloc(cChannels * sizeof MIXERCONTROLDETAILS_UNSIGNED);
MIXERCONTROLDETAILS mxcd = {sizeof(mxcd), pmxctrl->dwControlID,
cChannels, (HWND)0,
sizeof MIXERCONTROLDETAILS_UNSIGNED, (LPVOID) pUnsigned};
mixerGetControlDetails((HMIXEROBJ)hmx, &mxcd,
MIXER_SETCONTROLDETAILSF_VALUE);
// Set the volume to the middle (for both channels as needed)
pUnsigned[0].dwValue = pUnsigned[cChannels - 1].dwValue =
(pmxctrl->Bounds.dwMinimum+pmxctrl->Bounds.dwMaximum)/2;
mixerSetControlDetails((HMIXEROBJ)hmx, &mxcd,
MIXER_SETCONTROLDETAILSF_VALUE);
free(pmxctrl);
free(pUnsigned);
}
else
free(pmxctrl);
mixerClose(hmx);
}
void SelectMic()
{
// Open the mixer device
HMIXER hmx;
mixerOpen(&hmx, 0, 0, 0, 0);
// Get the line info for the wave in destination line
MIXERLINE mxl;
mxl.cbStruct = sizeof(mxl);
mxl.dwComponentType = MIXERLINE_COMPONENTTYPE_DST_WAVEIN;
mixerGetLineInfo((HMIXEROBJ)hmx, &mxl,
MIXER_GETLINEINFOF_COMPONENTTYPE);
// Find a LIST control, if any, for the wave in line
LPMIXERCONTROL pmxctrl = (LPMIXERCONTROL)malloc(mxl.cControls * sizeof
MIXERCONTROL);
MIXERLINECONTROLS mxlctrl = {sizeof mxlctrl, mxl.dwLineID, 0,
mxl.cControls, sizeof MIXERCONTROL, pmxctrl};
mixerGetLineControls((HMIXEROBJ) hmx, &mxlctrl,
MIXER_GETLINECONTROLSF_ALL);
// Now walk through each control to find a type of LIST control. This
// can be either Mux, Single-select, Mixer or Multiple-select.
DWORD i;
for(i=0; i < mxl.cControls; i++)
if (MIXERCONTROL_CT_CLASS_LIST == (pmxctrl[i].dwControlType
&MIXERCONTROL_CT_CLASS_MASK))
break;
if (i < mxl.cControls) { // Found a LIST control
// Check if the LIST control is a Mux or Single-select type
BOOL bOneItemOnly = FALSE;
switch (pmxctrl[i].dwControlType) {
case MIXERCONTROL_CONTROLTYPE_MUX:
case MIXERCONTROL_CONTROLTYPE_SINGLESELECT:
bOneItemOnly = TRUE;
}
DWORD cChannels = mxl.cChannels, cMultipleItems = 0;
if (MIXERCONTROL_CONTROLF_UNIFORM & pmxctrl[i].fdwControl)
cChannels = 1;
if (MIXERCONTROL_CONTROLF_MULTIPLE & pmxctrl[i].fdwControl)
cMultipleItems = pmxctrl[i].cMultipleItems;
// Get the text description of each item
LPMIXERCONTROLDETAILS_LISTTEXT plisttext =
(LPMIXERCONTROLDETAILS_LISTTEXT)
malloc(cChannels * cMultipleItems * sizeof
MIXERCONTROLDETAILS_LISTTEXT);
MIXERCONTROLDETAILS mxcd = {sizeof(mxcd), pmxctrl[i].dwControlID,
cChannels,
(HWND)cMultipleItems, sizeof MIXERCONTROLDETAILS_LISTTEXT,
(LPVOID) plisttext};
mixerGetControlDetails((HMIXEROBJ)hmx, &mxcd,
MIXER_GETCONTROLDETAILSF_LISTTEXT);
// Now get the value for each item
LPMIXERCONTROLDETAILS_BOOLEAN plistbool =
(LPMIXERCONTROLDETAILS_BOOLEAN)
malloc(cChannels * cMultipleItems * sizeof
MIXERCONTROLDETAILS_BOOLEAN);
mxcd.cbDetails = sizeof MIXERCONTROLDETAILS_BOOLEAN;
mxcd.paDetails = plistbool;
mixerGetControlDetails((HMIXEROBJ)hmx, &mxcd,
MIXER_GETCONTROLDETAILSF_VALUE);
// Select the "Microphone" item
for (DWORD j=0; j<cMultipleItems; j = j + cChannels)
if (0 == strcmp(plisttext[j].szName, "Microphone"))
// Select it for both left and right channels
plistbool[j].fValue = plistbool[j+ cChannels - 1].fValue = 1;
else if (bOneItemOnly)
// Mux or Single-select allows only one item to be selected
// so clear other items as necessary
plistbool[j].fValue = plistbool[j+ cChannels - 1].fValue = 0;
// Now actually set the new values in
mixerSetControlDetails((HMIXEROBJ)hmx, &mxcd,
MIXER_GETCONTROLDETAILSF_VALUE);
free(pmxctrl);
free(plisttext);
free(plistbool);
}
else
free(pmxctrl);
mixerClose(hmx);
}
Additional query words:
4.00 kbdsd waveInOpen waveInAddBuffer new type waveaudio
Keywords : kbmm MMMixer MMWave
Version : WINDOWS:4.0
Platform : WINDOWS
Issue type :