The following example uses the capFileSetCaptureFile macro to specify an alternate filename (MYCAP.AVI) for the capture file and the capFileAlloc macro to preallocate a file of 5 MB.
char szCaptureFile[] = "MYCAP.AVI";
capFileSetCaptureFile( hWndC, szCaptureFile);
capFileAlloc( hWndC, (1024L * 1024L * 5));