重新連線您的輸入，以確保特定輸出類型

發行項
07/28/2023

[與此頁面相關的功能 DirectShow是舊版功能。它已被 MediaPlayer、 IMFMediaEngine和 Media Foundation 中的音訊/視訊擷取取代。這些功能已針對Windows 10和Windows 11進行優化。 Microsoft 強烈建議新程式碼盡可能使用 MediaPlayer、 IMFMediaEngine 和 音訊/視訊擷取 ，而不是 DirectShow。 Microsoft 建議盡可能重寫使用舊版 API 的現有程式碼，以使用新的 API。]

篩選準則會實作 IAMStreamConfig：：SetFormat 方法，以在連接篩選的針腳之前設定音訊或視訊格式。如果您的輸出釘選已連線，而且您可以提供新類型，則請重新連線您的 PIN，但只有在其他篩選準則可以接受新類型時。如果其他篩選準則無法接受媒體類型，則呼叫 SetFormat 並讓連線保持獨立。

除非已連接轉換針腳，否則轉換篩選準則可能沒有任何慣用的輸出類型。在此情況下， SetFormat 和 IAMStreamConfig：：GetStreamCaps 方法應該會傳回VFW_E_NOT_CONNECTED，直到輸入針腳連線為止。否則，這些方法可以如往常般運作。

在某些情況下，當您在已建立的連線上提供格式時，重新連接針腳會很有用。例如，假設篩選可以將 24 位 RGB 視訊壓縮成 X 格式，而且可以將 8 位 RGB 視訊壓縮成 Y 格式。輸出針腳可以執行下列任一動作：

一律在 GetStreamCaps中同時提供 X 和 Y，並一律接受 SetFormat中的 X 和 Y。
如果輸入類型為 24 位 RGB，請提供並接受只格式化 X。如果輸入類型為 8 位 RGB，請提供並接受 Y 格式。如果輸入針腳未連接，則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重新連線的程式碼：

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;
}

共用方式為

重新連線您的輸入，以確保特定輸出類型

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