Selecting ltmmCapture Object Compressors for C

// define helper macros for using interfaces under C 
#ifndef COBJMACROS 
   #define COBJMACROS 
#endif 
 
#include "ltmm.h" 
#include "resource.h" 
#include "tchar.h" 
#include "stdio.h" 
 
HINSTANCE g_hInstance; // application instance handle 
IltmmCapture* g_pCapture; // convert object's interface pointer 
 
// 
// BuildCompressorList 
// fills a listbox to match the contents of the collection 
// 
// pCompressors = compressor collection's interface pointer 
// hwndListBox = listbox window handle 
// 
void BuildCompressorList(IltmmCompressors* pCompressors, HWND hwndListBox)  
{ 
   long i;  
   long count;  
   int selected = -1;  
 
   // reset the listbox contents 
   SendMessage(hwndListBox, LB_RESETCONTENT, 0, 0);  
 
   // get the collection's item count 
   IltmmCompressors_get_Count(pCompressors, &count);  
 
   for(i = 0; i < count; i++) 
   { 
      IltmmCompressor* pCompressor;  
      BSTR bstr;  
      TCHAR sz[256];  
      int index;  
      VARIANT_BOOL f;  
 
      // retrieve collection item 
      IltmmCompressors_Item(pCompressors, i, &pCompressor);  
 
      // get displayable name 
      IltmmCompressor_get_FriendlyName(pCompressor, &bstr);  
 
      // convert from unicode 
      _stprintf(sz, _T("%ls"), bstr);  
 
      // free name 
      SysFreeString(bstr);  
 
      // add the name to the listbox 
      index = SendMessage(hwndListBox, LB_ADDSTRING, 0, (LPARAM) (LPCTSTR) sz);  
 
      // associate the listbox item with the collection item index 
      SendMessage(hwndListBox, LB_SETITEMDATA, index, i);  
 
      // remember this listbox item, if it is selected in the collection 
      IltmmCompressor_get_Selected(pCompressor, &f);  
      if(f)  
         selected = i;  
 
      // free the collection item 
      IUnknown_Release(pCompressor);  
   } 
 
   // select the appropriate listbox item 
   for(i = 0; i < count; i++) 
   { 
      if(selected == (long) SendMessage(hwndListBox, LB_GETITEMDATA, i, 0))  
      { 
         SendMessage(hwndListBox, LB_SETCURSEL, i, 0);  
         break;  
      } 
   } 
 
} 
 
// 
// CompressorSelectionChanged 
// called to reflect changes in the listbox selection 
// 
// pCompressors = compressor collection's interface pointer 
// hwndListBox = listbox window handle 
// 
void CompressorSelectionChanged(IltmmCompressors* pCompressors, HWND hwndListBox)  
{ 
   int index;  
   long item;  
   int i;  
   int count;  
   HRESULT hr;  
 
   // get the index of current listbox selection 
   index = (int) SendMessage(hwndListBox, LB_GETCURSEL, 0, 0);  
 
   if(index < 0)  
   { 
      // clear selection 
      IltmmCompressors_put_Selection(pCompressors, -1);  
   } 
   else 
   { 
 
      // get the collection item index 
      item = (long) SendMessage(hwndListBox, LB_GETITEMDATA, index, 0);  
 
      // select the item 
#ifdef _DEBUG 
      { 
         IltmmCompressor* pCompressor;  
         IltmmCompressors_Item(pCompressors, item, &pCompressor);  
         hr = IltmmCompressor_put_Selected(pCompressor, VARIANT_TRUE);  
         IUnknown_Release(pCompressor);  
      } 
#else 
      hr = IltmmCompressors_put_Selection(pCompressors, item);  
#endif 
      // if new selection failed, we need to force the listbox to match the actual selection 
      if(FAILED(hr))  
      { 
         // get the real selection 
         IltmmCompressors_get_Selection(pCompressors, &item);    
 
         // find the matching listbox item 
         count = (int) SendMessage(hwndListBox, LB_GETCOUNT, 0, 0);  
 
         for(i = 0; i < count; i++) 
         { 
            if(item == (long) SendMessage(hwndListBox, LB_GETITEMDATA, i, 0))  
            { 
               SendMessage(hwndListBox, LB_SETCURSEL, i, 0);  
               break;  
            } 
         } 
 
      } 
 
   } 
 
} 
 
// 
// RefreshCompressorList 
// called when to completely rebuild the collection 
// 
// pCompressors = compressor collection's interface pointer 
// hwndListBox = listbox window handle 
// 
void RefreshCompressorList(IltmmCompressors* pCompressors, HWND hwndListBox)  
{ 
   IltmmCompressor* pCompressor;  
   long item;  
   BSTR bstr;  
 
 
   // get the currently selected item    
   IltmmCompressors_get_Selection(pCompressors, &item);  
 
   if(item >= 0)  
   { 
      // get it's unique name 
      IltmmCompressors_Item(pCompressors, item, &pCompressor);  
      IltmmCompressor_get_Name(pCompressor, &bstr);  
      IUnknown_Release(pCompressor);  
   } 
   else 
   { 
      bstr = NULL;  
   } 
 
   // rebuild the collection 
   IltmmCompressors_Refresh(pCompressors);  
 
   if(bstr)  
   { 
      // find the previously selected item 
      IltmmCompressors_Find(pCompressors, bstr, &item);  
 
      // make it the current selection 
      if(item >= 0)  
 
         IltmmCompressors_put_Selection(pCompressors, item);  
 
      SysFreeString(bstr);  
   } 
 
   // rebuild the listbox 
   BuildCompressorList(pCompressors, hwndListBox);  
} 
 
// 
// CompressorDlgProc 
// selects object compressors 
// 
BOOL CALLBACK CompressorDlgProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)  
{ 
   IltmmCompressors* pCompressors;  
 
 
   wParam = wParam ; 
   lParam = lParam ; 
 
   switch (msg)  
   { 
   case WM_INITDIALOG:  
      // initialize the audio compressor listbox 
      IltmmCapture_get_AudioCompressors(g_pCapture, &pCompressors);  
      BuildCompressorList(pCompressors, GetDlgItem(hwnd, IDC_AUDIOCOMPRESSORS));  
      IUnknown_Release(pCompressors);  
 
      // initialize the video compressor listbox 
      IltmmCapture_get_VideoCompressors(g_pCapture, &pCompressors);  
      BuildCompressorList(pCompressors, GetDlgItem(hwnd, IDC_VIDEOCOMPRESSORS));  
      IUnknown_Release(pCompressors);  
 
      return TRUE;  
      break;  
 
   case WM_COMMAND:  
      switch(LOWORD(wParam))  
      { 
      case IDC_REFRESHAUDIOCOMPRESSORS:  
         // refresh the audio compressor listbox 
         IltmmCapture_get_AudioCompressors(g_pCapture, &pCompressors);  
         RefreshCompressorList(pCompressors, GetDlgItem(hwnd, IDC_AUDIOCOMPRESSORS));  
         IUnknown_Release(pCompressors);  
         return TRUE;  
         break;  
      case IDC_AUDIOCOMPRESSORS:  
         if(HIWORD(wParam) == LBN_SELCHANGE)  
         { 
            // select the audio compressor 
            IltmmCapture_get_AudioCompressors(g_pCapture, &pCompressors);  
            CompressorSelectionChanged(pCompressors, GetDlgItem(hwnd, IDC_AUDIOCOMPRESSORS));  
            IUnknown_Release(pCompressors);  
         } 
         break;  
 
      case IDC_REFRESHVIDEOCOMPRESSORS:  
         // initialize the video compressor listbox 
         IltmmCapture_get_VideoCompressors(g_pCapture, &pCompressors);  
         RefreshCompressorList(pCompressors, GetDlgItem(hwnd, IDC_VIDEOCOMPRESSORS));  
         IUnknown_Release(pCompressors);  
         return TRUE;  
         break;  
 
      case IDC_VIDEOCOMPRESSORS:  
         if(HIWORD(wParam) == LBN_SELCHANGE)  
         { 
            // select the video compressor 
            IltmmCapture_get_VideoCompressors(g_pCapture, &pCompressors);  
            CompressorSelectionChanged(pCompressors, GetDlgItem(hwnd, IDC_VIDEOCOMPRESSORS));  
            IUnknown_Release(pCompressors);  
         } 
         break;  
 
      case IDOK:  
         EndDialog(hwnd, IDOK);  
         return TRUE;  
         break;  
      } 
      break;  
   } 
   return FALSE;  
 
} 
 
void SelectingltmmCaptureObjectCompressors_Example ( HINSTANCE hInstance /*application instance handle*/ ) 
{ 
   HRESULT hr;  
 
   g_hInstance = hInstance;  
 
   // initialize COM library 
   hr = CoInitialize(NULL);  
   if(FAILED(hr))  
      goto error;  
 
   // create the convert object 
   hr = CoCreateInstance(&CLSID_ltmmCapture, NULL, CLSCTX_INPROC_SERVER, &IID_IltmmCapture, (void**) &g_pCapture);  
   if(FAILED(hr))  
      goto error;  
 
 
   DialogBox(g_hInstance, (LPCTSTR)IDD_COMPRESSORDLG, NULL, CompressorDlgProc);  
 
 
error:  
   // cleanup 
 
   if(g_pCapture)  
      IUnknown_Release(g_pCapture);  
 
   CoUninitialize(); 
}