Create a custom DirectShow Filter SDK DLL

To create a new DirectShow® filter, all you need to do is to implement a standard Dynamic Link Library (DLL). A valid DLL must provide (export) the functions declared in the FilterSDKLib.h include file. Additionally, to compile the DLL, it must be linked against FilterSDKLib.lib. This library file encapsulates the code for a complete DirectShow® filter utilizing the FilterSDK.axwrapper. The FilterSDK.ax is a DirectShow® filter proxy which loads all available Filter SDK DLLs and registers them as DirectShow® filters. Also the DLL must provide a couple of global variables containing information about the filter.

To speed up the development, the MontiVision Development Kit includes two  wizards  which create DLLs as described above. The wizards are capable of creating a project for Microsoft Visual C++ 6.0 or 7.0 (.NET). The wizards create a skeleton source file with all of the necessary functions. All you have to do is to populate the functions with your custom code. For more information on creating a DLL project using wizards, have a look at the wizards help page.

The settings of the new filter can be accessed through the filters IMVFilterSDK COM interface. The filter provides a property page for graphical configuration within the MontiVision Workbench. New controls for the custom paramters of the filters may be added to this property page and control the filter through IMVFilterSDK.

Attention: Make sure you set up your development enviroment as described in the installation page.

DLL Functions:

The functions your DLL has to implement are as follows. Be careful not to declare them as static functions.

STDAPI TransformSample( BYTE*        pInBuffer, 
                        BYTE*        pOutBuffer, 
                        int          iWidth,  
                        int          iHeight,  
                        int          iBytePerPixel,
                        int          iPitch,
                        void*        pSavePointer,
                        void*        pTempPointer, 
                        PVOID        pIOInBuffer, 
                        int          iIOInBufferSize, 
                        PVOID        pIOOutBuffer, 
                        int          iIOOutBufferSize,
                        SAMPLE_TIMES times);

This is the transform function of the filter. It is called for every frame that is to be processed by the filter. Have a look at this  help page  for more information on the transform function.

Parameter:

typedef struct _SAMPLE_TIMES
{
    LONGLONG timeStart;
    LONGLONG timeEnd;
    LONGLONG timeMediaStart;
    LONGLONG timeMediaEnd;
}SAMPLE_TIMES;

Parameter:

STDAPI InitDLL( void** ppSavePointer, void** ppTempPointer );

This function is called once directly after the DLL is loaded. This si where all the initialization should be done. The ppSavePointer is used for any data your filter needs to store between function calls. It could point to a variable or perhaps a structure. The ppSavePointer is passed to every function call, so do not use global variables! This is because your filter would have a single instance of its global variables per application and multiple instances of the filter would access the same data.

STDAPI UninitDLL( void* pSavePointer, void* pTempPointer );

This function is called right before the DLL is unloaded. Use this function to clean up the filter, for example freeing allocated memory.

Parameter:

STDAPI GetSizeOfParameters( DWORD *pdwSize, void* pSavePointer );

This function sets the pdwSize parameter to the size of the filters parameter block.

Parameter:

STDAPI SaveParameters( void* pData, void* pSavePointer )

This function is called when a filter graph is saved to a MontiVision Project file (*.mvp). Copy your configuration data from your parameter block in pSavePointer to pData.

Parameter:

STDAPI LoadParameters( void* pData, void* pSavePointer )

This function is called when a filter graph is loaded from a MontiVision Project file (*.mvp). Copy your configuration from the pData to your parameter block in pSavePointer.

Parameter:

STDAPI PropActivate(HWND hwnd, void* pSavePointer, void* pTempPointer);

The PropActivate functon is called when opening the filters property page. Initialize the filter property page within this function. Look at the macros in windowsx.h to write code with enhanced readability.

Parameter:

STDAPI PropDeactivate(HWND hwnd, void* pSavePointer, void* pTempPointer);

The PropDeactivate functon is called when closing the filters property page.

Parameter:

STDAPI PropApplyChanges(HWND hwnd, void* pSavePointer, void* pTempPointer);

The PropApplyChanges functon is called on the Apply button of the filters property dialog. Save the values of the dialog controls if nessasary.

Parameter:

int PropReceiveMessage(HWND hwnd,
                                           UINT uMsg,
                                           WPARAM wParam, 
                                           LPARAM lParam, 
                                           void* pSavePointer,
                                           void* pTempPointer, 
                                           BOOL* bSetDirty);

The PropReceiveMessage functon is called on every windows message received by the property page. Handle the messages of the property page controls within this function.

Parameter:

DLL variables:

The following table includes all global variables the DLL has to export. Don't declare them as static variables.

I/O Pin Types: