Selecting ltmmCapture Object Compressors for C

The following example shows how to enumerate and select ltmmCapture object compressors.

// define helper macros for using interfaces under C
#define COBJMACROS

#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; 
   
   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; 
   
}

   
int APIENTRY WinMain(HINSTANCE hInstance, 
                     HINSTANCE hPrevInstance, 
                     LPSTR     lpCmdLine, 
                     int       nCmdShow) 
{
   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();
   
   return 0; 
}