Selecting ltmmConvert Object Compressors for C++

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

#include "ltmm.h"
#include "resource.h"
#include "tchar.h"
#include "stdio.h"

HINSTANCE g_hInstance;  // application instance handle
IltmmConvert* g_pConvert; // capture 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
   pCompressors->get_Count(&count);
   for(i = 0; i < count; i++)
   {
      IltmmCompressor* pCompressor;
      BSTR bstr;
      TCHAR sz[256];
      int index;
      VARIANT_BOOL f;
      // retrieve collection item
      pCompressors->Item(i, &pCompressor);
      // get displayable name
      pCompressor->get_FriendlyName(&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
      pCompressor->get_Selected(&f);
      if(f)
         selected = i;
      // free the collection item
      pCompressor->Release();
   }
   // 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
      pCompressors->put_Selection(-1);
   }   else
   {  
      // get the collection item index
      item = (long) SendMessage(hwndListBox, LB_GETITEMDATA, index, 0);
      // select the item
#ifdef _DEBUG
      {  
         IltmmCompressor* pCompressor;
         pCompressors->Item(item, &pCompressor);
         hr = pCompressor->put_Selected(VARIANT_TRUE);
         pCompressor->Release();
      }
#else
      hr = pCompressors->put_Selection(item);
#endif
      // if new selection failed, we need to force the listbox to match the actual selection
      if(FAILED(hr))
      {  
         // get the real selection
         pCompressors->get_Selection(&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
   pCompressors->get_Selection(&item);
   if(item >= 0)
   {
      // get it's unique name
      pCompressors->Item(item, &pCompressor);
      pCompressor->get_Name(&bstr);
      pCompressor->Release();
   }
   else
   {  
      bstr = NULL;
   }
   // rebuild the collection
   pCompressors->Refresh();
   if(bstr)
   {
      // find the previously selected item
      pCompressors->Find(bstr, &item);

      // make it the current selection
      if(item >= 0)

         pCompressors->put_Selection(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
      g_pConvert->get_AudioCompressors(&pCompressors);
      BuildCompressorList(pCompressors, GetDlgItem(hwnd, IDC_AUDIOCOMPRESSORS));
      pCompressors->Release();
      // initialize the video compressor listbox
      g_pConvert->get_VideoCompressors(&pCompressors);
      BuildCompressorList(pCompressors, GetDlgItem(hwnd, IDC_VIDEOCOMPRESSORS));
      pCompressors->Release();
      return TRUE;
      break;
   case WM_COMMAND:
      switch(LOWORD(wParam))
      {  
      case IDC_REFRESHAUDIOCOMPRESSORS:
         // refresh the audio compressor listbox
         g_pConvert->get_AudioCompressors(&pCompressors);
         RefreshCompressorList(pCompressors, GetDlgItem(hwnd, IDC_AUDIOCOMPRESSORS));
         pCompressors->Release();
         return TRUE;
         break;
      case IDC_AUDIOCOMPRESSORS:
         if(HIWORD(wParam) == LBN_SELCHANGE)
         {  
            // select the audio compressor
            g_pConvert->get_AudioCompressors(&pCompressors);
            CompressorSelectionChanged(pCompressors, GetDlgItem(hwnd, IDC_AUDIOCOMPRESSORS));
            pCompressors->Release();
         }  
         break;
      case IDC_REFRESHVIDEOCOMPRESSORS:
         // initialize the video compressor listbox
         g_pConvert->get_VideoCompressors(&pCompressors);
         RefreshCompressorList(pCompressors, GetDlgItem(hwnd, IDC_VIDEOCOMPRESSORS));
         pCompressors->Release();
         return TRUE;
         break;
      case IDC_VIDEOCOMPRESSORS:
         if(HIWORD(wParam) == LBN_SELCHANGE)
         {  
            // select the video compressor
            g_pConvert->get_VideoCompressors(&pCompressors);
            CompressorSelectionChanged(pCompressors, GetDlgItem(hwnd, IDC_VIDEOCOMPRESSORS));
            pCompressors->Release();
         }  
         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 capture object
   hr = CoCreateInstance(CLSID_ltmmConvert, NULL, CLSCTX_INPROC_SERVER, IID_IltmmConvert, (void**) &g_pConvert);
   if(FAILED(hr))
      goto error;

   DialogBox(g_hInstance, (LPCTSTR)IDD_COMPRESSORDLG, NULL, CompressorDlgProc); error:
   // cleanup
   if(g_pConvert)
      g_pConvert->Release();
   CoUninitialize();
   return 0;
}