SAMPLE: Using mciSendString() to Change an .AVI Palette

• Microsoft Windows Software Development Kit (SDK) version 3.1
• Microsoft Win32 Software Development Kit (SDK) version 3.5
• Microsoft Video for Windows Development Kit (VfWDK) version 1.1

SUMMARY

The SETPAL sample demonstrates how to use the "setvideo palette handle to" Media Control Interface (MCI) string to change the palette that will be used when an Audio-Video Interleaved (.avi) file is played.

The following file is available for download from the Microsoft Software Library:

 ~ Setpal.exe

   ARTICLE-ID: Q119591
   TITLE     : How to Obtain Microsoft Support Files from Online Services

MORE INFORMATION

The basic steps to supply your own palette are as follows:

1. Fill in a LOGPALETTE structure containing the color information for your palette.

2. Create a logical palette using the CreatePalette() function.

3. Call mciSendString() (or mciSendCommand()) to supply that palette to the AVI file using a string such as:

         setvideo <alias> palette handle to <palette handle>
   

The SETPAL sample can be compiled as a 32-bit sample, called SETPAL32, or as a 16-bit sample, called SETPAL16. As a result, it is compatible with Windows 95, Windows NT, and Windows 3.1. Setpal32.mak and Setpal16.mak make files are provided. SETPAL16 requires the Video for Windows 1.1 Development Kit to build successfully.

SETPAL is a sample application that allows opening an .avi file via the open common dialog box. Menu choices allow the .avi file to be opened, played, stopped, or closed. MCI strings perform the underlying work. The following MCI string is used to supply a palette for the .avi file:

    setvideo <alias> palette handle to <palette handle>

Excerpts from Setpal.c

   // include files
   #include <windows.h>  // Required for all Windows applications
   #include "windowsx.h" // for GlobalAllocPtr/GlobalFreePtr in
                         // CreateSamplePalette.
   #include "mmsystem.h" // For the MCI calls.

   // global variables
   static HPALETTE g_hPal = NULL;    // Palette handle.
   .
   .
   .

   // CreateSamplePalette() demonstrates how to fill in a LOGPALETTE
   // structure and create a logical palette
   VOID CreateSamplePalette(void)

   {
       LPLOGPALETTE lpLogPal;
       int          i;
       int          nPalEntries = 236;   // Number of entries in our
                                         // palette.
                                         // 256 are possible, but the
                                         // system reserves 20 of them.

       lpLogPal = (LPLOGPALETTE) GlobalAllocPtr (GHND,
                   sizeof (LOGPALETTE) + nPalEntries * sizeof
                   (PALETTEENTRY));

          lpLogPal->palVersion    = 0x300;
       lpLogPal->palNumEntries = nPalEntries;

       for (i = nPalEntries; i > 0; i--)
       {
           // Fill in the red, green, and blue values for our palette.
           // This particular palette is a wash from green to black.
           lpLogPal->palPalEntry[i].peRed   = 0;
           lpLogPal->palPalEntry[i].peGreen = i;
           lpLogPal->palPalEntry[i].peBlue  = 0;

           // Create unique palette entries. This flag may change depending
           // on your purposes. See the Windows API documentation
           // concerning the PALETTEENTRY structure for more information.
           lpLogPal->palPalEntry[i].peFlags = PC_NOCOLLAPSE;
       }

       // Create the logical palette.
       g_hPal = CreatePalette (lpLogPal);

       // Clean up.
       GlobalFreePtr (lpLogPal);
   }

   // The ProcessAVICommands() function in SETPAL.C handles the open, set
   // palette, play, and close for the AVI file. Once the AVI file has been
   // opened, issue an mciSendString() such as the following to set the
   // palette:

   static char szAlias[10] = "paltest";  // the movie alias to use in
   mciSendString                         // buffer to hold the MCI
   char szBuffer[128];                   // string we built.
   .
   .
   .
      wsprintf(szBuffer, "setvideo %s palette handle to %d",
              (LPSTR)szAlias, g_hPal);
      mciSendString(szBuffer, NULL, 0, NULL);