directshow原理分析之filter到filter的连接

标签：directshow

Filter是Directshow中最基本的概念。Directshow使用filter graph来管理filter。filter graph是filter的容器。

Filter一般由一个或者几个Pin组成。filter之间通过Pin来连接，组成一条链。

PIN也是一种COM组件，每一个PIN都实现了IPin接口。

试图链接的两个Pin必须在一个filter graph中。

连接过程如下：

1.Filter Graph Manager在输出pin上调用IPin::Connect

2.如果输出Pin接受连接，则调用IPin::ReceiveConnection

3.如果输入Pin也接受此次连接，则双方连接成功

首先来分析基类函数CBasePin的Connect实现：

CBasePin继承了IPin。

<pre name="code" class="cpp">HRESULT __stdcall CBasePin::Connect(IPin * pReceivePin, __in_opt const AM_MEDIA_TYPE *pmt   // optional media type)
{
    CheckPointer(pReceivePin,E_POINTER);
    ValidateReadPtr(pReceivePin,sizeof(IPin));
    CAutoLock cObjectLock(m_pLock);
    DisplayPinInfo(pReceivePin);

    /* 检查该Pin是否早已连接 */
    if (m_Connected) {
        DbgLog((LOG_TRACE, CONNECT_TRACE_LEVEL, TEXT("Already connected")));
        return VFW_E_ALREADY_CONNECTED;
    }

    /*一般Filter只在停止状态下接受连接*/
    if (!IsStopped() && !m_bCanReconnectWhenActive) {
        return VFW_E_NOT_STOPPED;
    }

    /*开始媒体类型检查，找出一种双方均支持的类型*/
    const CMediaType * ptype = (CMediaType*)pmt;
    HRESULT hr = AgreeMediaType(pReceivePin, ptype);
    if (FAILED(hr)) {
        DbgLog((LOG_TRACE, CONNECT_TRACE_LEVEL, TEXT("Failed to agree type")));

        // Since the procedure is already returning an error code, there
        // is nothing else this function can do to report the error.
        EXECUTE_ASSERT( SUCCEEDED( BreakConnect() ) );

#ifdef DXMPERF
        PERFLOG_CONNECT( (IPin *) this, pReceivePin, hr, pmt );
#endif // DXMPERF

        return hr;
    }

    DbgLog((LOG_TRACE, CONNECT_TRACE_LEVEL, TEXT("Connection succeeded")));

#ifdef DXMPERF
    PERFLOG_CONNECT( (IPin *) this, pReceivePin, NOERROR, pmt );
#endif // DXMPERF

    return NOERROR;
}

Connect两个参数分别代表：输出Pin试图链接的输入Pin和指定连接用的媒体类型。

真正的链接是CBase::AgreeMediaType来实现的。

<pre name="code" class="cpp">HRESULT CBasePin::AgreeMediaType(IPin *pReceivePin, const CMediaType *pmt)
{
    ASSERT(pReceivePin);
    IEnumMediaTypes *pEnumMediaTypes = NULL;

    // 判断pmt是不是一个完全指定的媒体类型
    if ( (pmt != NULL) && (!pmt->IsPartiallySpecified())) {
	//用这个指定的媒体类型去做连接，如果失败不做任何处理。
        return AttemptConnection(pReceivePin, pmt);
    }


    /* 进行pin上支持的媒体类型的枚举 ，开始媒体类型的协商过程*/
    HRESULT hrFailure = VFW_E_NO_ACCEPTABLE_TYPES;

    for (int i = 0; i < 2; i++) {
        HRESULT hr;
        if (i == (int)m_bTryMyTypesFirst) {
            hr = pReceivePin->EnumMediaTypes(&pEnumMediaTypes);
        } else {
            hr = EnumMediaTypes(&pEnumMediaTypes);
        }
        if (SUCCEEDED(hr)) {
            ASSERT(pEnumMediaTypes);
            hr = TryMediaTypes(pReceivePin,pmt,pEnumMediaTypes);
            pEnumMediaTypes->Release();
            if (SUCCEEDED(hr)) {
                return NOERROR;
            } else {
                // try to remember specific error codes if there are any
                if ((hr != E_FAIL) &&
                    (hr != E_INVALIDARG) &&
                    (hr != VFW_E_TYPE_NOT_ACCEPTED)) {
                    hrFailure = hr;
                }
            }
        }
    }

    return hrFailure;
}

函数AttempConnection进行连接。

但是如果pmt是一个空指针或者不是完全指定的媒体类型，那么真正的协商过程也就开始了。注意，for循环的次数为2，输出Pin上的成员变量

m_bTryMyTypesFirst初始值为false，也就是说，连接过程进行到这里，会首先得到输入pin上的媒体类型枚举器的试连接，如果连接不成功，再去得到

输出Pin上的媒体类型枚举器的试连接。

下面看一下TryMediaTypes函数的实现：

HRESULT CBasePin::TryMediaTypes(IPin *pReceivePin, __in_opt const CMediaType *pmt, IEnumMediaTypes *pEnum)
{
    /* 复位枚举器内部状态 */

    HRESULT hr = pEnum->Reset();
    if (FAILED(hr)) {
        return hr;
    }

    CMediaType *pMediaType = NULL;
    ULONG ulMediaCount = 0;

    // attempt to remember a specific error code if there is one
    HRESULT hrFailure = S_OK;

    for (;;) {

        /* Retrieve the next media type NOTE each time round the loop the
           enumerator interface will allocate another AM_MEDIA_TYPE structure
           If we are successful then we copy it into our output object, if
           not then we must delete the memory allocated before returning */

        hr = pEnum->Next(1, (AM_MEDIA_TYPE**)&pMediaType,&ulMediaCount);
        if (hr != S_OK) {
            if (S_OK == hrFailure) {
                hrFailure = VFW_E_NO_ACCEPTABLE_TYPES;
            }
            return hrFailure;
        }


        ASSERT(ulMediaCount == 1);
        ASSERT(pMediaType);

        // 检查当前枚举得到的类型是否与不完全指定的类型参数匹配

        if (pMediaType &&
            ((pmt == NULL) ||
            pMediaType->MatchesPartial(pmt))) {
<span style="white-space:pre">	</span>    //进行试连接
            hr = AttemptConnection(pReceivePin, pMediaType);

            // attempt to remember a specific error code
            if (FAILED(hr) &&
            SUCCEEDED(hrFailure) &&
            (hr != E_FAIL) &&
            (hr != E_INVALIDARG) &&
            (hr != VFW_E_TYPE_NOT_ACCEPTED)) {
                hrFailure = hr;
            }
        } else {
            hr = VFW_E_NO_ACCEPTABLE_TYPES;
        }

        if(pMediaType) {
            DeleteMediaType(pMediaType);
            pMediaType = NULL;
        }

        if (S_OK == hr) {
            return hr;
        }
    }
}

最后需要看一下AttempConnection函数的跟Pin连接相关的虚函数的调用的顺序，对与自己实现filter有指导意义：

<pre name="code" class="cpp">HRESULT CBasePin::AttemptConnection(IPin* pReceivePin,      // connect to this pin
  					const CMediaType* pmt   // using this type
)
{
    // The caller should hold the filter lock becasue this function
    // uses m_Connected.  The caller should also hold the filter lock
    // because this function calls SetMediaType(), IsStopped() and
    // CompleteConnect().
    ASSERT(CritCheckIn(m_pLock));

    // Check that the connection is valid  -- need to do this for every
    // connect attempt since BreakConnect will undo it.
    HRESULT hr = CheckConnect(pReceivePin);
    if (FAILED(hr)) {
        DbgLog((LOG_TRACE, CONNECT_TRACE_LEVEL, TEXT("CheckConnect failed")));

        // Since the procedure is already returning an error code, there
        // is nothing else this function can do to report the error.
        EXECUTE_ASSERT( SUCCEEDED( BreakConnect() ) );

        return hr;
    }
    //可以显示媒体类型，有时候挺有用
    DisplayTypeInfo(pReceivePin, pmt);

    /* Pin上的媒体类型检查 */

    hr = CheckMediaType(pmt);
    if (hr == NOERROR) {

        /*  Make ourselves look connected otherwise ReceiveConnection
            may not be able to complete the connection
        */
        m_Connected = pReceivePin;
        m_Connected->AddRef();
        hr = SetMediaType(pmt);//在Pin上保存媒体类型
        if (SUCCEEDED(hr)) {
            /* 询问连接对方Pin是否能接受当前的媒体类型 */

            hr = pReceivePin->ReceiveConnection((IPin *)this, pmt);
	    //连接成功
            if (SUCCEEDED(hr)) {
                /* Complete the connection */

                hr = CompleteConnect(pReceivePin);
                if (SUCCEEDED(hr)) {
                    return hr;
                } else {
                    DbgLog((LOG_TRACE,
                            CONNECT_TRACE_LEVEL,
                            TEXT("Failed to complete connection")));
                    pReceivePin->Disconnect();
                }
            }
        }
    } else {
        // we cannot use this media type

        // return a specific media type error if there is one
        // or map a general failure code to something more helpful
        // (in particular S_FALSE gets changed to an error code)
        if (SUCCEEDED(hr) ||
            (hr == E_FAIL) ||
            (hr == E_INVALIDARG)) {
            hr = VFW_E_TYPE_NOT_ACCEPTED;
        }
    }

    // BreakConnect and release any connection here in case CheckMediaType
    // failed, or if we set anything up during a call back during
    // ReceiveConnection.

    // Since the procedure is already returning an error code, there
    // is nothing else this function can do to report the error.
    EXECUTE_ASSERT( SUCCEEDED( BreakConnect() ) );

    /*  If failed then undo our state */
    if (m_Connected) {
        m_Connected->Release();
        m_Connected = NULL;
    }

    return hr;
}

这些均是在输出Pin上的CompleteConnect中完成的。

CBaseOutPin继承自CBasePin

HRESULT CBaseOutputPin::CompleteConnect(IPin *pReceivePin)
{
    UNREFERENCED_PARAMETER(pReceivePin);
    return DecideAllocator(m_pInputPin, &m_pAllocator);
}

<pre name="code" class="cpp">HRESULT CBaseOutputPin::DecideAllocator(IMemInputPin *pPin, __deref_out IMemAllocator **ppAlloc)
{
    HRESULT hr = NOERROR;
    *ppAlloc = NULL;

    // get downstream prop request
    // the derived class may modify this in DecideBufferSize, but
    // we assume that he will consistently modify it the same way,
    // so we only get it once
    ALLOCATOR_PROPERTIES prop;
    ZeroMemory(&prop, sizeof(prop));

    // 询问输入Pin对于分配器的需求
    pPin->GetAllocatorRequirements(&prop);

    // if he doesn't care about alignment, then set it to 1
    if (prop.cbAlign == 0) {
        prop.cbAlign = 1;
    }

    /* 询问输入Pin是否提供一个分配器 */

    hr = pPin->GetAllocator(ppAlloc);
    if (SUCCEEDED(hr)) {
       //决定Sample使用的内存的大小，以及分配器管理的Sample的数量
        hr = DecideBufferSize(*ppAlloc, &prop);
        if (SUCCEEDED(hr)) {
            //通知输入Pin最终使用的分配器的对象
            hr = pPin->NotifyAllocator(*ppAlloc, FALSE);
            if (SUCCEEDED(hr)) {
                return NOERROR;
            }
        }
    }

    /* 如果输入Pin上不提供分配器，则必须在输出Pin上提供 */

    if (*ppAlloc) {
        (*ppAlloc)->Release();
        *ppAlloc = NULL;
    }

    /* 创建一个输出Pin上的分配器 */

    hr = InitAllocator(ppAlloc);
    if (SUCCEEDED(hr)) {

        // note - the properties passed here are in the same
        // structure as above and may have been modified by
        // the previous call to DecideBufferSize
        hr = DecideBufferSize(*ppAlloc, &prop);
        if (SUCCEEDED(hr)) {
            hr = pPin->NotifyAllocator(*ppAlloc, FALSE);
            if (SUCCEEDED(hr)) {
                return NOERROR;
            }
        }
    }

    /* Likewise we may not have an interface to release */

    if (*ppAlloc) {
        (*ppAlloc)->Release();
        *ppAlloc = NULL;
    }
    return hr;
}

HRESULT CBaseOutputPin::Active(void)
{
    if (m_pAllocator == NULL) {
        return VFW_E_NO_ALLOCATOR;
    }
    return m_pAllocator->Commit();
}

directshow原理分析之filter到filter的连接

标签：directshow

原文地址：http://blog.csdn.net/rootusers/article/details/42145787