[bst]

This should work.
You can call it
$dll(DLLNAME.dll, GetBSPMovieName, 0) and you will get full path
or
$dll(DLLNAME.dll, GetBSPMovieName, 1) for filename without path.

int __stdcall GetBSPMovieName(HWND mWnd, HWND aWnd, char *data, char *parms, BOOL show, BOOL nopause)
{

	HWND bsp_hand;
	if ( (bsp_hand = FindWindow("BSPlayer",NULL)) !=0 ) {
		COPYDATASTRUCT cds;

		char buf[MAX_PATH];
		void *adr;
		adr=&buf;

		cds.dwData=BSP_GetFileName;
		cds.lpData=&adr;
		cds.cbData=4;
		SendMessage(bsp_hand,WM_COPYDATA,(WPARAM)aWnd,(LPARAM)&cds);

		if (strcmp(data,"0")==0) 
			strcpy(data, buf);
		else
		{
			char *p=strrchr(buf,'\\');
			strcpy(data, ++p);
		}

		return 3;
	}

	return 1;

}