重新連線您的輸入，以確保特定輸出類型

發行項
03/26/2025

[與此頁面相關聯的功能，DirectShow是舊版功能。它已被 MediaPlayer、IMFMediaEngine以及媒體基金會中的音訊/視訊擷取所取代。這些功能已針對 Windows 10 和 Windows 11 進行優化。 Microsoft強烈建議新程式代碼盡可能在媒體 基礎中使用 MediaPlayer、IMFMediaEngine 和 音訊/視訊擷取，而不是 DirectShow。 Microsoft建議使用舊版 API 的現有程式代碼，盡可能改寫成使用新的 API。]

篩選會實作 IAMStreamConfig：：SetFormat 方法，以在連接篩選的針腳之前設定音訊或視訊格式。如果您的輸出端點已連接，並且您可以提供新的類型，請重新連接您的端點，但前提是其他過濾器能夠接受新的類型。如果另一個篩選無法接受媒體類型，則使對 SetFormat 的呼叫失敗，並保持連線不變。

轉換過濾器不會有任何偏好的輸出類型，除非其輸入端子已連接。在此情況下，SetFormat 和 IAMStreamConfig::GetStreamCaps 方法應該傳回 VFW_E_NOT_CONNECTED，直到輸入接腳連線為止。否則，這些方法可以照常運作。

在某些情況下，當您在已建立的連線上提供或支援格式時，重新連接接腳會很有用。例如，假設濾波器可以將 24 位元 RGB 視訊壓縮成 X 格式，並且可以將 8 位元 RGB 視訊壓縮成格式 Y。輸出接腳可以執行以下兩項中的一項：

請在 GetStreamCaps中始終提供 X 和 Y，並在 SetFormat中始終接受 X 和 Y。
如果輸入類型為 24 位 RGB，則只接受和使用 X 格式。如果輸入類型為 8 位 RGB，則僅支援且接受 Y 格式。如果輸入針腳未連接，這兩種方法都會失敗。

不論是哪一種情況，您都需要一些看起來像這樣的重連代碼：

HRESULT MyOutputPin::CheckMediaType(const CMediaType *pmtOut)
{
    // Fail if the input pin is not connected.
    if (!m_pFilter->m_pInput->IsConnected()) {
        return VFW_E_NOT_CONNECTED;
    }

    // (Not shown: Reject any media types that you know in advance your 
    // filter cannot use. Check the major type and subtype GUIDs.)

    // (Not shown: If SetFormat was previously called, check whether
    // pmtOut exactly matches the format that was specified in SetFormat.
    // Return S_OK if they match, or VFW_E_INVALIDMEDIATYPE otherwise.)
   
    // Now do the normal check for this media type.
    HRESULT hr;
    hr = m_pFilter->CheckTransform(
        &m_pFilter->m_pInput->CurrentMediaType(),  // The input type.
        pmtOut  // The proposed output type.
    );
    if (hr == S_OK)
    {
        // This format is compatible with the current input type.
        return S_OK;
    }
 
    // This format is not compatible with the current input type. 
    // Maybe we can reconnect the input pin with a new input type.
    
    // Enumerate the upstream filter's preferred output types, and 
    // see if one of them will work.
    CMediaType *pmtEnum;
    BOOL fFound = FALSE;
    IEnumMediaTypes *pEnum;
    hr = m_pFilter->m_pInput->GetConnected()->EnumMediaTypes(&pEnum);
    if (hr != S_OK)
    {
        return E_FAIL;
    }
    while (hr = pEnum->Next(1, (AM_MEDIA_TYPE **)&pmtEnum, NULL), hr == S_OK)
    {
        // Check this input type against the proposed output type.
        hr = m_pFilter->CheckTransform(pmtEnum, pmtOut);
        if (hr != S_OK) 
        {
            DeleteMediaType(pmtEnum);
            continue; // Try the next one.
        }

        // This input type is a possible candidate. But, we have to make
        // sure that the upstream filter can switch to this type. 
        hr = m_pFilter->m_pInput->GetConnected()->QueryAccept(pmtEnum);
        if (hr != S_OK) 
        {
            // The upstream filter will not switch to this type.
            DeleteMediaType(pmtEnum);
            continue; // Try the next one.
        }
        fFound = TRUE;
        DeleteMediaType(pmtEnum);
        break;
    }
    pEnum->Release();

    if (fFound)
    {
        // This output type is OK, but if we are asked to use it, we will
        // need to reconnect our input pin. (See SetFormat, below.)
        return S_OK;
    }
    else
    {
        return VFW_E_INVALIDMEDIATYPE;
    }
}

HRESULT MyOutputPin::SetFormat(AM_MEDIA_TYPE *pmt)
{
    CheckPointer(pmt, E_POINTER);
    HRESULT hr;

    // Hold the filter state lock, to make sure that streaming isn't 
    // in the middle of starting or stopping:
    CAutoLock cObjectLock(&m_pFilter->m_csFilter);

    // Cannot set the format unless the filter is stopped.
    if (m_pFilter->m_State != State_Stopped)
    {
        return VFW_E_NOT_STOPPED;
    }

    // The set of possible output formats depends on the input format,
    // so if the input pin is not connected, return a failure code.
    if (!m_pFilter->m_pInput->IsConnected())
    {
        return VFW_E_NOT_CONNECTED;
    }

    // If the pin is already using this format, there's nothing to do.
    if (IsConnected() && CurrentMediaType() == *pmt)
    {
        return S_OK;
    }

    // See if this media type is acceptable.
    if ((hr = CheckMediaType((CMediaType *)pmt)) != S_OK) 
    {
        return hr;
    }

    // If we're connected to a downstream filter, we have to make
    // sure that the downstream filter accepts this media type.
    if (IsConnected()) 
    {
        hr = GetConnected()->QueryAccept(pmt);
        if (hr != S_OK)
        {
            return VFW_E_INVALIDMEDIATYPE;
        }
    }

    // Now make a note that from now on, this is the only format allowed,
    // and refuse anything but this in the CheckMediaType code above.

    // Changing the format means reconnecting if necessary.
    if (IsConnected())
    {
        m_pFilter->m_pGraph->Reconnect(this);
    }

    return NOERROR;
}


// Override CTransformFilter::SetMediaType to reconnect the input pin. 
// This method is called immediately after the media type is set on a pin.
HRESULT MyFilter::SetMediaType(
    PIN_DIRECTION direction, 
    const CMediaType *pmt
)
{
    HRESULT hr;
    if (direction == PINDIR_OUTPUT) 
    {
        // Before we set the output type, we might need to reconnect 
        // the input pin with a new type.
        if (m_pInput && m_pInput->IsConnected()) 
        {
            // Check if the current input type is compatible.
            hr = CheckTransform(
                    &m_pInput->CurrentMediaType(),
                    &m_pOutput->CurrentMediaType());
            if (SUCCEEDED(hr))
            {
                return S_OK;
            }
            // Otherwise, we need to reconnect the input pin.
            // Note: The CheckMediaType method has already called 
            // QueryAccept on the upstream filter. 
            hr = m_pGraph->Reconnect(m_pInput);
            return hr;
        }
    }
    return S_OK;
}

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重新連線您的輸入，以確保特定輸出類型

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