如何编写Filter

 

  注册 Filter

      AX 文件的一个对外接口 DllRegisterServer ，由外部调用，比如注册 AX 的时候： regsvr32 xxx.ax

 

       通常情况下，我们的 filter 可能注册在 ”Direct Show” 目录下，那么直接调用

       // Creates registry entries for the DLL

STDAPI DllRegisterServer ()

{

return AMovieDllRegisterServer2(TRUE) ;

}

 

AMovieDllRegisterServer2 在 DX 的帮助文档内的说明如下：

The AMovieDllRegisterServer2 function creates registry entries for every component in the g_Templates array. However, this function has some limitations. First, it assigns every filter to the "DirectShow Filters" category (CLSID_LegacyAmFilterCategory), but not every filter belongs in this category. Capture filters and compression filters, for example, have their own categories. Second, if your filter supports a hardware device, you might need to register two additional pieces of information that AMovieDLLRegisterServer2 does not handle: the medium and the pin category. A medium defines a method of communication in a hardware device, such as a bus. The pin category defines the function of a pin. For information on mediums, see KSPIN_MEDIUM in the Microsoft Windows Driver Development Kit (DDK). For a list of pin categories, see Pin Property Set.

      

       如果我们的引擎需要注册到 DirectShow 之外的目录，又该如何做？

       // 注册 Filter 到 Video Compressor

REGFILTER2 rf2FilterReg =

{

    1,                                    // Version 1 (no pin mediums or pin category).

    MERIT_NORMAL,       // Merit.

    1,                                   // Number of pins.

    &sudPins                    // Pointer to pin information.

};

 

//Creates registry entries for the DLL

STDAPI DllRegisterServer( void)

{

    HRESULT hr = E_FAIL;

    IFilterMapper2 *pFM2 = NULL;

 

    hr = AMovieDllRegisterServer2(TRUE);                // 这个还是要调用的

    if (FAILED(hr))       return hr;

hr = CoCreateInstance( CLSID_FilterMapper2, NULL,

                                           CLSCTX_INPROC_SERVER,

                                                     IID_IFilterMapper2, (void **)&pFM2);

 

    if (FAILED(hr))       return hr;

 

    hr = pFM2->RegisterFilter( CLSID_SomeFilter,                        // Filter CLSID.

                                                    g_wszName,                                   // Filter name.

                                                    NULL,                                               // Device moniker.

                                                   &CLSID_VideoCompressorCategory,           // Video compressor category.

                                                   g_wszName,                                   // Instance data.

                                                   &rf2FilterReg                                    // Pointer to filter information.

                                                   );

    pFM2->Release();

    return hr;

}

 

注销 Filter

注销 DirectShow 内的引擎

// Removes registry entries for the DLL

STDAPI DllUnregisterServer ()

{

return AMovieDllRegisterServer2(FALSE) ;

}

 

       注销指定目录下的引擎

       // 注销 Video Compressor 下的引擎

       // Removes registry entries for the DLL

STDAPI DllUnregisterServer()

{

    HRESULT hr = E_FAIL;

    IFilterMapper2* pFM2 = NULL;

 

    hr = AMovieDllRegisterServer2(FALSE);

    if (FAILED(hr))       return hr;

 

    hr = CoCreateInstance(CLSID_FilterMapper2, NULL, CLSCTX_INPROC_SERVER,

                                IID_IFilterMapper2, (void **)&pFM2);

    if (FAILED(hr))       return hr;

 

    hr = pFM2->UnregisterFilter(&CLSID_VideoCompressorCategory,

                                             g_wszName, CLSID_SomeFilter);

 

    pFM2->Release();

    return hr;

}

 

给 Filter 起个名字

// Pin 的 type 分为 Major Type 和 Subtype

// 比如， Major Type = Video, Subtype = MPEG-2

const  AMOVIESETUP_MEDIATYPE sudPinTypes =

{

&MEDIATYPE_NULL,            // Major type

&MEDIASUBTYPE_NULL           // Subtype

};

 

const  AMOVIESETUP_PIN psudPins[] =

{

       // 定义 Input Pin 的信息

{

L"Input",                 // String pin name

FALSE,             // Is it rendered

FALSE,             // Is it an output

FALSE,             // Allowed none

FALSE,             // Allowed many

&CLSID_NULL,        // Connects to filter

0           // Connects to pin

1,                  // Number of types

& sudPinTypes

} ,      // The pin details

{

L"Output",          // String pin name

FALSE,              // Is it rendered

TRUE,               // Is it an output

FALSE,              // Allowed none

FALSE,              // Allowed many

&CLSID_NULL,        // Connects to filter

0,          // Connects to pin

1,                  // Number of types

&sudPinTypes        // The pin details

       }

};

 

// Declare filter information

const AMOVIESETUP_FILTER sudFilter =

{

& CLSID_MPKiller ,       // Filter CLSID

L" HQ MP Killer ",        // Filter name

0x8800000 ,                    // Its merit

2 ,                      // Number of pins

psudPins                       // Pin details

};

 

// declare a global array of CFactoryTemplate class instances, named g_Templates . Each

// CFactoryTemplate class contains registry information for one filter. Several filters can

// reside in a single DLL; simply include additional CFactoryTemplate entries. You can

// also declare other COM objects, such as property pages

// 在同一个 DLL 或者 AX 内，可以有多个引擎，比如系统目录下的 quartz.dll 。

// 所以，如果有多个引擎，相应的数组的大小就是引擎的个数。

CFactoryTemplate g_ Templates[] =

{

{

L"HQ MP Killer",

&CLSID_MPKiller,

CImplement ::CreateInstance ,

NULL,

&sudFilter

}

};

 

int g_cTemplates = sizeof(g_Templates) / sizeof(g_Templates[0]);       // 有几个引擎

 

允许 Filter 应用

// CreateInstance 是 CFactory 的一个接口，在 Filter 内部实现它

CUnknown* WINAPI CImplement::CreateInstance(     LPUNKNOWN pUnk,

                                                                                    HRESULT *pHr)

{

    CImplement *pFilter = new CImplement ();

    if  (!pFilter)

    {

        *pHr = E_OUTOFMEMORY;

    }

    return pFilter;

}

 

Filter 的 Merit

Graph 会使用“傻子”机制联接不同的 filter ，这就要通过 filter 的 merit 值的高低进行“傻子”联接。

 

该联接要使用 IFilterMapper2::EnumMatchingFilters 方法。

Merit ：

enum

{

    MERIT_PREFERRED     = 0x800000,

    MERIT_NORMAL        = 0x600000,

    MERIT_UNLIKELY      = 0x400000,

    MERIT_DO_NOT_USE    = 0x200000,

    MERIT_SW_COMPRESSOR = 0x100000,

    MERIT_HW_COMPRESSOR = 0x100050

};

<= MERIT_DO_NOT_USE 的 Merit 的 Filter ，系统是不会去“傻子”联接的。当然 Merit 值可以是 任意值 ，而不一定是枚举出来的。

 

确定 Filter 的用途

不同的 Filter 有不同的用途，可以选择不同的基类，实现不同的方法。详见 DirectX 文档。 Filter 的种类，在内进行了详细的描述 root/DirectShow/DirectShow Reference/Constants and GUIDs/Filter Categories 。

 

添加属性页

CFactoryTemplate g _Templates[2] =

{

    {

              g_wszArcIPCam,                       // Name

              &CLSID_ArcIPCam,                  // CLSID

              CArcIPCam::CreateInstance, // Method to create an instance of MyComponent

              NULL,                                     // Initialization function

              &sudArcIPCamSourceFilter      // Set-up information (for filters)

    },

 

       {

                     // 这些数据，为属性页准备

              g_wszArcIPCamProperty,

              &CLSID_ArcIPCamProperty,

              CArcIPCamProperty::CreateInstance

       }

};

      

class CArcIPCam : public xxx, public IArcIPCam , public ISpecifyPropertyPages

{

private:

    // Constructor is private because you have to use CreateInstance

    CArcIPCam(IUnknown *pUnk, HRESULT *phr);

    ~CArcIPCam();

 

    CArcIPCamPin *m_pPin;

 

public:

    static CUnknown * WINAPI CreateInstance(IUnknown *pUnk, HRESULT *phr); 

    DECLARE_IUNKNOWN;

 

           // Property Page---

           STDMETHODIMP GetClassID(CLSID *pClsid);

    // Basic COM - used here to reveal our property interface.

    STDMETHODIMP NonDelegatingQueryInterface(REFIID riid, void ** ppv);

    // return our property pages

    STDMETHODIMP GetPages(CAUUID * pPages);

 }

       这三个函数必须实现。